Aquaculture Nutrition
doi: 10.1111/j.1365-2095.2010.00816.x
2011
..............................................................................................
1
1
1
2
1,3
Aquaculture & Fisheries Development Centre, School of Biological, Earth & Environmental Sciences, University College Cork,
Distillery Fields, North Mall, Cork, Ireland; 2 Kerry BioScience Ltd., Kilnagleary, Carrigaline, County Cork, Ireland;
3
Department of Zoology, Ecology & Plant Science, School of Biological, Earth & Environmental Sciences, University College
Cork, Cork, Ireland
As part of a programme to develop sustainable diets for
macroalgivores, a 3-month experiment was conducted to
determine the effects of konjac glucomannan–xanthan gum
(KX) binder configuration on formulated feed stability, feed
palatability and growth performance of juvenile, hatcheryreared, Haliotis discus hannai. This study was conducted in a
recirculation facility in which four KX binder configurations
were evaluated in a series of isonitrogenous experimental
feeds and freshly harvested Laminaria digitata was included
as a natural feed type. Dry matter leaching of the experimental feed treatments was assessed with no significant difference in the dry matter leaching between treatments
observed. No differences (P > 0.05) were found in percentage survival, daily food consumption (DFC) and linear
growth rate (LGR) between treatments. Food conversion
efficiency (FCE), specific growth rate (SGR) and body
weight/shell length (BW/SL) ratio were significantly higher
when offered L. digitata. Trends showed that the best performing KX feed in terms of FCE, LGR, SGR and BW/SL
ratio was produced with the 2% KX; 1 : 1 binder.
KEY WORDS:
abalone, binder, feed production, growth, Haliotis, nutrition
Received 4 March 2010, accepted 2 July 2010
Correspondence: Maria OÕMahoney, Aquaculture & Fisheries Development
Centre, University College Cork, Distillery Fields, North Mall, Cork,
Ireland. E-mail: [email protected]
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2011 Blackwell Publishing Ltd
It is widely accepted that aquaculture is pivotal to the future
maintenance of commercial fishery markets. Key challenges
that are faced by the industry include issues of sustainability,
feed availability and technological challenges to improve
production efficiency. For abalone culture, commercial feeds
exist, but the low uptake by producers in Ireland continues to
put pressure on local marine ecosystems because natural
harvests of marine kelp continue to be used as the primary
feed source. When harvested sustainably, i.e. a stump of
25 cm is left intact; regeneration can take 3–5 years (Werner
& Kraan 2004). However, the impact of locally intensive
harvesting of near-shore kelp beds can result in slow regeneration times and altered community structure (Kelly 2005).
Multiple stakeholders in the aquaculture sector in Ireland
have nominated feed development and availability as a
priority research focus for this sector. This research was
conducted as part of a feed development programme for high
value shellfish species in Ireland.
Recent FAO statistics indicate that world capture production of abalone has declined in all producing countries. Maximal output of abalone aquaculture existed in just two of
the thirteen producing countries, China and Korea, in 2007
(FAO 2009). The high market value of abalone suggests that
intensification of commercial abalone culture is necessary to
sustain market demands. A diet that reduces the reliance on
non-sustainable feed sources is critical to commercial viability.
Target nutritional requirements for several commercially
lucrative species of abalone have been identified through
considerable research in recent decades. Regionally developed artificial feeds exist for locally produced species, and
a number of feeds produced by extrusion cooking are
available. However, high importation costs have restricted
widespread use of currently available feeds in some regions.
The application of cost-effective, innovative feed production
technologies is necessary to achieve a locally dynamic and
internationally competitive aquaculture industry.
Binder configuration is important for abalone feed development because of the perceived influence on feed palatability. A review by Fleming et al. (1996) outlined the pivotal
role of feed binders in commercially focussed artificial feed
development for abalone. For abalone, previous studies have
shown that binder strength and feed palatability are negatively correlated (Uki et al. 1985; Gorfine 1991). Similarly, a
negative relationship between consumption and feed toughness has been demonstrated for Haliotis rubra and Haliotis
midae offered natural macroalgae species (Day & Cook 1995;
Fleming 1995). Coupled with this, leaching of feed attractants from artificial feeds is desirable in intensive culture
whereby the naturally passive feeding nature of abalone may
benefit from stimulation (Harada et al. 1996; Mai 1998;
Fermin 2003; Troell et al. 2006).
Hydrocolloids (e.g. gelatin, guar gum, sodium alginate,
agar, carrageenan, carboxymethylcellulose) as feed binders
are advantageous for artificial feed production because they
are easy to produce in small scale, and the effectiveness of
hydrocolloid-bound on-growing feeds has been demonstrated
for several aquatic species such as shrimp (De Muylder et al.
2008; Palma et al. 2008), sea urchins (Caltagirone et al. 1992;
Pearce et al. 2002; Mortensen et al. 2003), abalone (Uki et al.
1985; Knauer et al. 1993; Britz 1996a; Coote et al. 1996),
tilapia (Fagbenro & Jauncey 1995), crayfish (Ruscoe et al.
2005), sole (Liu et al. 2008) and rainbow trout (Storebakken
& Austreng 1987). However, some hydrocolloid binders such
as gelatin and sodium alginate are expensive, and their use in
formulated feed development may be prohibitive to overall
low-cost feed production goals. Other hydrocolloid binders
are more cost-effective as feed binders, and applications of
these binders have often been demonstrated in other areas.
Two such binders are konjac glucomannan and xanthan gum.
Konjac is a glucomannan polysaccharide obtained from the
tubers of Amorphophallus konjac and has a linear backbone
of (1 fi 4)-linked b-D-mannose and b-D-glucose, in the ratio
1.6 : 1 (Kato & Matsuda 1969). Solubility is conferred by the
presence of acetyl groups (approximately, 1 acetyl group per
17 residues) at the C-6 position, and short oligosaccharide
side chains at the C-3 position of the mannoses. Xanthan
gum is an extracellular polysaccharide derived from the
bacterium, Xanthomonas campestris, which is a naturally
occurring pathogen of the brassicas (Kelco 2007). Xanthan
gum has a (1 fi 4)-linked linear backbone of b-D-glucose, as
in cellulose, and is solubilized by charged trisaccharide side
chains attached at O-3 of alternate glucose residues to give a
pentasaccharide repeating sequence (Melton et al. 1976). On
cooling and/or addition of salt, it undergoes a co-operative
conformational transition (Morris et al. 1977) from a disordered coil to a rigid ordered structure (5-fold helix). Solutions
of xanthan gum in its ordered conformation show tenuous
‘‘weak gel’’ properties, which appear to arise from weak
association between the helical sequences, and are sensitive to
ionic environment. Xanthan gum alone, however, does not
give ÔtrueÕ (self-supporting) gels, but will form strong
and cohesive gels when mixed with konjac glucomannan
(Goycoolea et al. 1995). The exact mechanism of gel formation is not yet established, but probably involves association
of ÔsmoothÕ regions of the (1 fi 4)-diequatorially linked of
konjac glucomannan to the cellulosic backbone of xanthan
(also (1 fi 4)-diequatorially linked). The formation of recognizable gels was found at total polysaccharide levels of only
0.02%, which is the lowest gelling concentration observed for
a carbohydrate system (Dea 1993). Both konjac glucomannan
and xanthan gum have been widely used in the food industry.
The formation of the gel network in the presence of the feed
physically entraps the material. Any interactions with the
components contained within the feed would result in the
compromised formation of this network. Applications of the
konjac glucomannan–xanthan gum binders have been demonstrated in other areas (e.g. pharmaceutical and prosthetics)
(Eyo-okon & Hilton 2003; Alvarez-Manceñido et al. 2008;
Fan et al. 2008), but this binder complex has not previously
been evaluated for aquatic feed production.
Considerable development studies of the konjac glucomannan–xanthan gum (KX) binder for use in aquatic feeds
has identified three major variables in the KX binder configuration for artificial feeds (i) the use of seawater (SW) or
distilled water (DW) in binder preparation, (ii) overall binder
concentration and (iii) the ratio of K to X (OÕMahoney
2009). The aim of this study was to assess a formulated feed
with four forms of the KX binder on feed palatability and the
growth performance of cultured Haliotis discus hannai. The
results of this study were pivotal to further feed development
for H. discus hannai using the KX binder.
Konjac glucomannan (KJ2B) was obtained from Mannasol
Products Ltd (Cheshire, UK) and xanthan gum (Keltrol [E])
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
was obtained from CP Kelco (Surrey, UK). Laminaria digitata meal was obtained from Arramara Teoranta (Co. Galway, Ireland), soy protein isolate was obtained from Holland
and Barrett (Cork, Ireland), CaCO3 was obtained from
Sigma-Aldrich Ltd (Dorset, UK), and vitamins and minerals
were obtained from Inform Nutrition (Cork, Ireland).
Experimental feeds in this study were prepared according
to recently developed methodology for feed production
using the konjac glucomannan–xanthan gum binder
(OÕMahoney 2009). Dry feed ingredients were mixed for
10 min in a commercial food mixer. The konjac glucomannan and xanthan gum powders were weighed out in separate
batches at the required concentration and mixed to combine. The total volume of water (SW or DW) required was
placed in a stainless steel pot with a mixing paddle, and the
mixed powders were dispersed using a fine dredger. When
all the powders were dispersed, mixing was continued for
30 min. The viscous solution was placed in a hot water
bath (set temperature 85 C) and heated for 30 min after a
minimum internal gel temperature of 72 C was reached.
Dry feed ingredients and lipids were added to the hot gel
Table 1 Ingredient composition of the
experimental feeds (g dry matter kg)1)
Ingredients
KX binder
Laminaria
digitata meal
Soy protein isolate
CaCO3
Vitamins1
Minerals2
solution, and the composite feed was mixed in a commercial
food mixer for 3 min. The hot feed was poured into a rigid
container, cooled rapidly and refrigerated overnight. On the
following day, the feeds were sliced into strips and air-dried
in a drying room equipped with a convector heater and
dehumidifiers for 24–30 h (average temperature 30 C;
average relative humidity 28%). Air-dried feeds were stored
in air-tight containers.
To evaluate the key parameters of the KX binder configuration and the implications for H. discus hannai culture, an
experimental growth trial consisting of the following feed
treatments was conducted:
• Laminaria digitata
• 2% Distilled water K:X (1 : 3) (Diet A: DW 2% KX
1 : 3).
• 2% Seawater K:X (1 : 3) (Diet B: SW 2% KX 1 : 3).
• 2% Seawater K:X (1 : 1) (Diet C: SW 2% KX 1 : 1).
• 1.5% Seawater K:X (1 : 1) (Diet D: SW 1.5% KX 1 : 1).
The dietary treatments and feed ingredient composition
are shown in Table 1. Proximal composition and energy
composition of the feed treatments are shown in Table 2.
Diet A
Diet B
Diet C
Diet D
(DW 2%KX; 1 : 3) (SW 2%KX; 1 : 3) (SW 2%KX; 1 : 1) (SW 1.5%KX; 1 : 1)
174.7
319.7
174.7
319.7
174.7
319.7
174.7
319.7
352.9
107.2
14.9
30.6
352.9
107.2
14.9
30.6
352.9
107.2
14.9
30.6
352.9
107.2
14.9
30.6
DW, distilled water; KX, konjac glucomannan–xanthan gum; SW, seawater.
Vitamin premix composition per kg of experimental feed (Mai et al. 1995a) : thiamine HCl
120 mg; riboflavin 100 mg; folic acid 30 mg; PABA 400 mg; pyridoxine HCl 40 mg; niacin 800 mg;
Ca pantothenate 200 mg; inositol 4000 mg; ascorbic acid 4000 mg; biotin 12 mg; vitamin E
450 mg; menadione 80 mg; vitamin B12 0.18 mg; vitamin A 100 000 IU; vitamin D 2000 IU;
ethooxyquin 400 mg.
2
Mineral premix per kg of experimental feed (Mai et al. 1995a; Tan et al. 2001) : NaCl 0.4 g;
MgSO4.7H2O 6.0 g; NaH2PO4.2H2O 10.0 g; KH2PO4 20 g; Ca(H2PO4)2.H2O 8.0 g; ferric citrate
1.0 g; ZnSO4.7H2O 141.2 mg; MnSO4.2H2O 64.8 mg; CuSO4.5H2O 12.4 mg; CoCl2.6H2O 0.4 mg;
KIO3 1.2 mg; Na2SeO3 0.4 mg.
1
Table 2 Proximal composition of the
feed treatments (g kg)1 of dry matter)
Component
Diet A
(DW 2%KX;
1 : 3)
Diet B
(SW 2%KX;
1 : 3)
Diet C
(SW 2%KX;
1 : 1)
Diet D
(SW 1.5%KX;
1 : 1)
Laminaria
digitata
Protein1
Ash1
Carbohydrate1
Fat1
Energy2
387.6
303.0
306.4
3.1
11.74
361.0
363.0
275.2
0.9
10.68
361.3
360.0
278.3
0.4
10.72
357.0
362.6
276.5
3.9
10.75
148.4
285.1
516.3
50.2
13.02
DW, distilled water; KX, konjac glucomannan–xanthan gum; SW, seawater.
Values given as g kg)1 of dry matter.
2
Energy values in kJ g)1.
1
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
Hatchery-produced H. discus hannai [20–30 mm shell length
(SL)], which were reared on L. digitata, were collected from
Brandon Bay Seafoods, County Kerry, Ireland in February
2008 and transported to the Aquaculture & Fisheries
Development Centre, University College Cork (AFDC,
UCC) in large, cable-tied plastic bags that were dampened
internally with SW and pumped with oxygen to reduce gill
desiccation and aerobic stress (Sales & Britz 2001). Abalone
were maintained on a ration of L. digitata at the AFDC for
2 weeks to acclimate to the change in conditions.
The experimental system in this study consisted of a recirculation culture system consisting of 15 independent rectangular plastic tanks (320 mm L · 175 mm W · 150 mm H),
each containing a rearing unit composed of aquamesh lined
with corrugated plastic inserts. Each tank was aerated with a
centrally positioned airstone. The experimental system was
enclosed within a black surround such that abalone were
maintained in constant darkness throughout the study based
on evidence in Garcia-Esquivel et al. (2007). Outflow from
each tank was recirculated through a 2500- L SW reservoir
known as the Global Oceans System. Aeration in the SW
reservoir was maintained through a series of airlines lining
the base of the Global Oceans floor.
Water quality in the Global Oceans system was maintained
by weekly renewal of 50% of the SW capacity. Inflow into
the experimental tanks was monitored weekly using a
Palintest photometer to measure levels of ammonia
(0.18 ± 0.048 mg L)1 N), nitrite (0.02 ± 0.005 mg L)1 N),
nitrate (0.22 ± 0.034 mg L)1 N), pH (8.23 ± 0.004) and
alkalinity (186.67 ± 4.495 mg L)1 CaCO3). Salinity was
monitored on a weekly basis using a hand-held refractometer
and averaged at 35.5 ± 0.230 g L)1. SW temperature and
dissolved oxygen was monitored using the OxyGuard System
(OxyGuard, Birkerod, Denmark) and averaged at 17.33 ±
0.321 C and approximately 10.1 ± 0.08 mg L)1, respectively, over the duration of the study.
After the two week acclimation period, the H. discus hannai
were starved for 7 days prior to the initiation of the experiment. Individuals were drained of excess surface moisture
prior to measuring for individual SL (±0.1 mm) and weight
(±0.01 g) and randomly divided between 15 experimental
tanks (n = 15 tank)1). The initial stocking parameters of
each tank were 25.89 ± 0.18 mm SL and 2.79 ± 0.06 g live
weight (mean ± SE).
This study consisted of five experimental treatments of
which four feeds were novel formulated KX feeds. The
control treatment was fed locally harvested L. digitata. Three
replicates of each feed treatment were conducted. The
experimental set-up allowed interchanges of tank position at
each feeding interval for a completely randomized experimental design.
Feed replenishment was conducted every 3/4 days and abalone were fed ad libitum. Dry matter conversion factors for
the artificial feeds being fed throughout the trial were
obtained by drying five random samples of each diet in the
oven at 105 C overnight at the beginning of the experiment.
Fresh L. digitata was obtained from Ballycotton Bay, Co.
Cork approximately every 7–10 days and stored in an aerated SW tank at the AFDC. The L. digitata was removed
from the SW as required, and all epiphytes were removed. At
each feeding interval, a sample of the L. digitata frond used
in feeding was dried in an oven (n = 3) at 105 C for 24 h to
obtain a dry matter conversion factor for that feed. All
conversion factors for day 0 feeds were calculated as follows:
C ¼ d=w
where C = conversion factor, d = dry weight of the feed (g)
and w = wet weight of the feed (g).
Control samples (triplicate) of fresh L. digitata were run at
each feeding interval to correct for loss in macroalgal biomass in the absence of abalone. Correction factors for KX
feed consumption were determined from a dry matter
leaching assessment conducted at the end of the experiment.
Daily feed consumption rates (DFC) and food conversion
efficiencies (FCE) were calculated using the formula:
DFC ¼ ½ðFg Fu Þ=t=ðW Þ
where the DFC was the daily food consumption (DFC)
(mgdry matter g)1abalone day)1), Fg was the dry weight (g) of
food given during the experimental period, Fu was the dry
weight (g) of food uneaten during the experimental period,
W was the mean wet weight of abalone during the experimental period (assuming linear growth) and t was the time in
days. FCE was calculated from the formula:
FCE ¼ 100ðWf Wi Þ=ðFg Fu Þ
where FCE was the food conversion efficiency (%), Wf and
Wi were the final and initial whole abalone wet weights (g),
Fg was the dry weight of food given (g) during the experimental period, Fu was the dry weight of food uneaten (g)
during the experimental period.
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
Initial and final biometric data (length; mm and weight; g)
were recorded during this study to minimize the impact of
sampling intervals on overall H. discus hannai health and
homeostasis (Sales & Britz 2001). Growth rate was calculated
in terms of (i) SL (linear growth rate; LGR) and (ii) total
weight (specific growth rate; SGR) using the following
equations:
piece with the label corresponding to that day number (1–2)
was removed from the aquaria, drained on absorbent paper,
weighed and oven-dried at 105 C for 24 h to determine the
dry weight (g) of the feed piece. The dry matter leaching
(g kg)1) on each day was calculated using the equation:
LGR ðmm SL day1 Þ ¼ ðLf Li Þ=t
where, Do is the dry matter (g) in the original feed piece, Dm
is the dry matter (g) in the final feed piece after immersion in
SW.
SGR ð%day1 Þ ¼ 100ðlnWf lnWi Þ=t
where Li and Wi are initial length and weight, respectively,
Lf and Wf are the final length and weight, respectively, t is
the time (days) and ln is the natural log.
The body weight to SL ratio (BW/SL) was calculated at
the beginning of this study and for all experimental treatments at the end of the study using the equation:
BW : SL ðg mm1 Þ ¼ Mean weight=mean length
Each tank was checked for mortalities at each feeding
interval. Overall percentage survival (St) was calculated as
the ratio of the number of individuals surviving at the end of
experiment to the number of individuals at the beginning of
the experiment using the equation:
Dry matter loss ðg kg1 Þ ¼ ðDo Dm Þ=Do 103
Tank position was randomized throughout the experiment,
and the possibility of tank effects was assessed using a
randomized ANOVA at the end of the experiment. The
assumptions of normality were analysed using the
Kolmogorov–Smirnov or Shapiro–Wilks test. Comparisons
between groups of normal data were tested using ANOVA.
Non-normal data were compared using the non-parametric
Kruskal–Wallis test. Post hoc analyses were conducted using
the TUKEY multiple comparison test and the Kruskal–
Wallis multiple comparison test. All statistical analyses were
conducted using SPSS (Ver. 12.0.1 for Windows, SPSS Inc.,
Chicago, IL, USA). Significance was assumed when P < 0.05.
St ¼ Nt =No 100
where Nt is the number of abalone surviving at the end of
the experiment, and No is number of abalone at the
beginning of the experiment.
The initial abalone length and weight (mean ± SE) are
shown in Table 3. A one-way ANOVA indicated that there was
Tests to determine the dry matter leaching of the feed
treatments in this study in the absence of abalone were
conducted over 3/4 days at the end of this study in the
experimental system vessels. The dry matter loss values of the
formulated KX feeds were used for corrected consumption
estimates in this study.
The aquaria were labelled with the diet treatments of this
study (n = 3). Into each tank, two pieces of the appropriate
feed were placed. Each feed piece was preweighed and
labelled with a twine tag corresponding to the days of the
stability test (1st and 2nd). On day 0 of the stability test, dry
matter conversion factors for the feeds in the stability test
were obtained using identical procedures to those outlined
earlier (see Feeding, consumption and growth). These values
were used to calculate the average dry matter (g) in each feed
piece used in the SW stability test. On each day, the feed
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
Table 3 Initial abalone stocking parameters (mean ± SE; n = 15)
Tanks
Length (mm)
Weight (g)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
26.23
26.27
26.06
25.54
25.47
26.13
25.34
25.94
25.69
25.95
25.74
25.77
26.13
25.95
26.14
2.97
2.97
3.01
2.68
2.57
2.80
2.75
2.94
2.59
2.75
2.81
2.63
2.87
2.69
2.79
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.796
0.846
0.759
0.821
0.683
0.539
0.818
0.772
0.668
0.729
0.729
0.533
0.626
0.752
0.831
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.275
0.275
0.282
0.231
0.193
0.173
0.296
0.256
0.214
0.238
0.256
0.158
0.226
0.193
0.239
Immersion in SW resulted in dry matter loss in all experimental treatments (Table 4).
On day 3, no significant differences in cumulative dry
matter leaching between treatments were observed (Kruskal–
Wallis; d.f. = 4; H = 8.433; P = 0.077). On day 4, dry
matter loss across all treatments was not significantly different (Kruskal–Wallis; d.f. = 4; H = 7.833; P = 0.098).
At the end of the experiment, mean per cent survival ranged
from 91.11 ± 5.9% for Diet A treatment to 100.00 ± 0.0%
for abalone fed L. digitata (Table 5). There were no significant differences in the survival rates between treatments
(Kruskal–Wallis, d.f. = 4; H = 6.030, P = 0.197).
Table 4 Cumulative dry matter leaching (g kg)1; mean ± SE;
n = 3) of the experimental diets in this study
Treatment
Day 3
Day 4
Laminaria digitata
Diet A
(DW 2%KX; 1 : 3)
Diet B
(SW 2%KX; 1 : 3)
Diet C
(SW 2%KX; 1 : 1)
Diet D
(SW 1.5%KX; 1 : 1)
224.5 ± 39.9
459.6 ± 65.0
303.4 ± 12.7
419.4 ± 57.3
336.7 ± 26.0
404.1 ± 20.1
332.4 ± 13.8
489.5 ± 78.9
350.8 ± 5.3
472.5 ± 25.7
DW, distilled water; KX, konjac glucomannan–xanthan gum; SW,
seawater.
Experimental parameters over the duration of the stability test
were : temperature (C) = 16.24 ± 0.075; pH = 8.25 ± 0.002; O2
(mg L)1) = 10.5 ± 0.3.
Table 5 Percentage survival (mean ± SE; n = 3) of Haliotis discus
hannai in this study
Treatment
Survival (%)
Laminaria digitata
Diet A (DW 2%KX; 1 : 3)
Diet B (SW 2%KX; 1 : 3)
Diet C (SW 2%KX; 1 : 1)
Diet D (SW 1.5%KX; 1 : 1)
100.00
91.11
91.11
95.56
95.56
±
±
±
±
±
0.0
5.9
3.9
3.9
3.9
DW, distilled water; KX, konjac glucomannan–xanthan gum; SW,
seawater.
Mean DFC rates (mg DM g abalone)1 day)1) ranged from
5.43 ± 0.2 mg (L. digitata) to 8.26 ± 1.4 mg (Diet A).
There were no significant differences in the DFC of H. discus
hannai between treatments (ANOVA; d.f. = 4, 14; F = 3.074;
P = 0.068) (Fig. 1).
Laminaria digitata had a significantly higher FCE (6.79 ±
0.4% day)1 dry matter feed to wet weight gain) than the KX
experimental feeds in the current study (ANOVA; d.f. = 4, 14;
F = 43.707; P = 0.000) (Fig. 2). Within the KX feed
treatments, there was no significant difference in the observed
FCE.
Linear growth rate (LGR) No significant difference in the
LGR between the experimental treatments was observed
(ANOVA; d.f. = 4, 14; F = 3.537; P = 0.05) (Fig. 3). LGRs
ranged from 0.022 ± 0.001 mm day)1 (Diet D) to 0.058 ±
0.02 mm day)1 (L. digitata).
Specific growth rate (SGR) Laminaria digitata had the
highest SGR (0.56 ± 0.05% day)1) in this study, which was
significantly different to the novel KX feed treatments
(ANOVA; d.f. = 4, 14; F = 19.820; P = 0.000) (Fig. 4).
Within the novel feed treatments, SGR ranged from 0.14 ±
0.02% day)1 (Diet A) to 0.23 ± 0.07% day)1 (Diet C).
12
DFC (mg DM g abalone–1 day–1)
no significant difference in the mean weight of each treatment
(ANOVA; d.f. = 4, 224; F = 0.722; P = 0.578).
The possibility of tank effect was tested at the end of the
experiment by randomized complete block ANOVA with tank
as a factor. Tank effect was non-significant (P > 0.05).
10
8
6
4
2
0
L. digitata
Diet A
Diet B
Diet C
Diet D
Diet
Figure 1 Daily food consumption (DFC) (mgdry matter g)1 abalone
day)1; mean ± SE; n = 3) of each treatment. Differences in the
DFC between experimental treatments were non-significant (ANOVA,
d.f. = 4, 14; P = 0.068).
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
8
0.7
a
a
0.6
SGR (% day–1)
FCE (% day–1)
7
6
5
4
b
3
b
2
b
b
0.5
0.4
b
0.2
L. digitata
Diet A
b
Diet B
Diet C
Diet D
Diet
0
L. digitata
Diet A
Diet B
Diet C
Diet D
Figure 2 Food conversion efficiency (FCE) (% day)1 dry matter feed
to wet weight gain; mean ± S.E.; n = 3). Results showed that significant differences in the FCE were evident between Laminaria
digitata and the experimental KX feeds (ANOVA; d.f. = 4, 14;
P = 0.000). The results of the Tukey HSD are indicated by letters
above the bars. Where letters are not in common between bars
indicates significant differences between treatments (P < 0.05).
–1
b
0.1
0
1
b
0.3
0.08
0.07
0.06
0.05
0.04
Figure 4 Specific growth rate (SGR) (% day)1, mean ± SE, n = 3)
of the experimental treatments in this study. SGR was significantly
different between treatments (ANOVA; d.f. = 4, 14; P = 0.000). The
results of the Tukey HSD are indicated by letters above the bars.
Where letters are not in common between bars indicates significant
differences between treatments (P < 0.05).
Table 6 Body weight/shell length (BW/SL) ratios (mean ± SE;
n = 3) of the initial data and final dietary treatments of this study
Treatment
BW : SL (g mm)1)
Initial
Laminaria digitata
Diet A (DW 2%KX; 1 : 3)
Diet B (SW 2%KX; 1 : 3)
Diet C (SW 2%KX; 1 : 1)
Diet D (SW 1.5%KX; 1 : 1)
0.108
0.155
0.109
0.114
0.119
0.115
±
±
±
±
±
±
0.001a
0.001b
0.002ac
0.004cd
0.007d
0.001d
DW, distilled water; KX, konjac glucomannan–xanthan gum; SW,
seawater.
Letters indicate the results of the Kruskal–Wallis multiple comparison post hoc test. The values in the same column that do not have
the same superscript parameters were significantly different from
each other (P < 0.05).
0.03
0.02
0.01
0
L. digitata
Diet A
Diet B
Diet C
Diet D
Figure 3 Linear growth rate (LGR) (mm shell length day)1;
mean ± SE; n = 3) of the experimental feeds in this study. There
was no significant difference in the observed LGR between treatments (ANOVA; d.f. = 4, 14; P = 0.05).
Body weight/shell length ratio (BW/SL) Significant differences in the BW/SL ratios were evident in this study (Kruskal–Wallis; d.f. = 5; H = 15.822; P = 0.007) (Table 6).
The BW/SL ratio increased in all treatments when compared
with the initial BW/SL ratio (0.108 ± 0.001 g mm)1) but
Diet A (0.109 ± 0.002 g mm)1) did not show a significant
increase in BW/SL ratio over the duration of the study.
Laminaria digitata had the highest increase in BW/SL ratio
(0.155 ± 0.001 g mm)1) and was significantly higher than all
other experimental treatments at the end of this study. Diet C
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
(0.119 ± 0.007 g mm)1) had the highest BW/SL ratio of the
experimental KX feeds. This value was significantly different
to Diet A but not significantly different to Diet B
(0.114 ± 0.004 g mm)1) or Diet D (0.115 ± 0.001 g mm)1).
The results of the dry matter leaching assessment indicated
that dry matter leaching for the KX feeds did not differ
significantly to the control treatment, L. digitata. Varying the
concentration of KX and K to X ratios did not have a significant effect on dry matter leaching in this study. It was
perceived that four days is the maximum duration for SW
stability for these feeds because removal of these feeds after
day 4 was hindered by feed disaggregating. Grazing is a slow
feeding behaviour, and therefore abalone require that artificial feeds retain structural integrity in SW for at least 2 days
(Fleming et al. 1996). However, several studies report short
experimental periods of feed presentation ranging from 12 h
(Rivero & Viana 1996; Garcia-Esquivel et al. 2007) to 16 h
(Sales & Britz 2002a; b), whilst others report longer intervals
(3 days) between feeding to satiation (Mai 1998), and
therefore comparisons with this study are difficult to interpret.
Previous studies have reported that blending and finesieving of feed ingredients to <450 lm had a significant
influence on dry matter leaching of formulated feeds with
improved diet performance, measured as apparent digestibility coefficients, for abalone diets produced within this
particle size category (Sales & Britz 2002b). By contrast,
however, Obaldo et al. (1999) reported poorer diet performance for shrimp feeds at particle sizes <100 lm. Further
investigation to determine the optimal production method for
the novel KX feeds and factors that influence the property of
this binder for reduced dry matter leaching is required.
In this study, KX binder configuration did not significantly
affect diet performance on any parameter assessed. However,
the SGR achieved by the control treatment, L. digitata,
exceeded KX artificial diet performance in this parameter,
and overall, L. digitata had significantly higher FCE values
than all KX diet treatments.
Feed consumption rates in this study showed no significant
variability between all the experimental treatments. Although
non-significant, trends showed that the lowest DFC was
observed in the L. digitata treatment. The similarity of the
feeding rate, as measured by DFC, across all experimental
feed treatments suggests that feeding rate of H. discus hannai
for the feed treatments in this study was relatively constant
given the current feed formulations and experimental conditions. Abalone feed by repeated rasping action of the
radula, and it is likely that the relatively soft texture of fully
hydrated KX feeds influenced feeding rates. As a result,
comparable daily feed consumption rates for the KX feeds
and L. digitata were achieved despite the abalone having
been predisposed to L. digitata. Previous studies have related
consumption in H. rubra to physical (e.g. toughness) and
chemical (e.g. presence of phlorotannins) feed characteristics
rather than nutritional quality (Fleming 1995), and indeed
the South African abalone, H. midae, has been found to
select for softer textured red and green macroalgae over kelp
species in feed preference experiments (Day & Cook 1995). In
Ireland, anecdotal evidence from producers pertaining to the
development of H. discus hannai culture have indicated that
the ecologically abundant species of kelp, Laminaria hyperborea, was unsuitable for culture of H. discus hannai
purported to result from the tougher texture of this algal
species (Hession et al. 1998).
Consumption rates in culture studies of H. discus hannai is
not a well-documented experimental parameter. Numerous
foundation studies on this species (for example: Mai et al.
1994, 1995a,b, 1996; Mai 1998; Tan et al. 2002a,b; Park et al.
2008) have measured food conversion ratio (FCR), growth,
survival and compositional tissue analyses as indicator of
the dietary requirements of the species. Mai et al. (1995b)
describes consumption in abalone as a very difficult parameter to evaluate in relation to artificial feeds because of the
highly particulate nature of the feed ingredients and the
feeding mechanism of the abalone. In essence, there is no
quantitative evaluation of ingestion as a result of the rasping
action of the radula, and there is no reason to assume that all
feed particles removed as a result of the feeding action are
consumed by the individual. In field studies, the proportion
of food consumed in abalone (Haliotis sp.) has been found
to be an indicator of feed palatability in situations where
the environmental availability allows access to more than
one feed type (Tutschulte & Connell 1988). Mercer et al.
(1993) found that feeding rates of H. discus hannai
(0.1–0.4% BW day)1) on six species of algae (Alaria esculenta, L. digitata, L. saccharina, Ulva lactuca, Palmaria
palmata and Chrondris crispus) and two mixed feeds levelled
off after 10 weeks, indicating a habitual acclimation to the
feed, and subsequent analyses of feeding rates were not
conducted in their study. When compared with Mercer et al.
(1993), the feeding rates of this study indicate comparatively
low feeding rates for H. discus hannai (0.5–0.8% BW day)1)
on all feed treatments. Our evaluation of consumption
throughout this study did not show any evidence of habitual
acclimation to the experimental feeds, and further study of
this aspect of abalone feeding behaviour may be necessary to
maximize feeding potential for experimental feeds. The
plastic responses of abalone to varied feed types (GarciaEsquivel & Felbeck 2008) coupled with adaptive physiological processes suggests that, given time, abalone will consume
a range of feeds, and longer feeding trials would provide an
indication of adaptive feed responses.
The significantly higher FCE of the L. digitata treatment
in this study over all experimental KX feed treatments indicated that the nutrient utilization of H. discus hannai for
fresh L. digitata was better than the KX feed formulation
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
ingredients. The proximal composition analyses, outlined in
Table 2, indicated notable differences in protein, carbohydrate and lipid concentrations between the natural and
experimental feed types. The success of a formulated feed
type may be dependent on a series of factors including feed
digestibility, gut physiology, gut transition times and interactive effects of nutrient composition that were not evaluated
in this study. The efficiency with which dry matter feed was
converted to wet weight gain despite comparable consumption of L. digitata with the KX feeds may suggest an adaptive
response to this feed type. Haliotis discus hannai have associative gut microflora for particular feed types, and the
composition of the gut microflora has been shown to change
over time and with changes in feed (Tanaka et al. 2003). In
addition, a 6- month experiment conducted by GarciaEsquivel & Felbeck (2006) found that digestive enzyme
activity in various parts of the gut of Haliotis rufescens altered according to feed type.
It is suggested that the significantly higher FCE of
L. digitata in this study could have been as a result of a
history of feeding on L. digitata as this was the feed used at
the commercial hatchery from which the experimental
H. discus hannai were obtained. It is likely that the experimental abalone were adapted to L. digitata as a feed type
through acquired optimal gut digestion and nutrient utilization. It is therefore recommended that an adaptive period
should be allocated prior to growth assessment of artificial
feeds to remove any bias associated with previous feeding
history on growth assessment results (Pereira et al. 2007).
There are variable reports of acclimation periods for abalone
prior to experimental evaluation of formulated feeds in the
literature (Table 7). Further study is needed to determine the
optimal duration of acclimation period for experimental feed
types.
Table 7 Acclimation periods allocated
prior to abalone growth trials
Although no significant differences in the LGR between
treatments were evident in this study, the SGR indicated
that a higher SGR was observed in the L. digitata treatment. Haliotis discus hannai are slow growers achieving
approximately 1–2 cm growth in SL per year (Lee 2004).
Assuming linear growth, the LGR in this study of the
L. digitata treatment (0.058 ± 0.02 mm SL day)1) would
approximate to the maximum growth projected by Lee
(2004) in one year (2.1 cm year)1), and given that this
treatment was our experimental control, we evaluate the
growth achieved on the L. digitata treatment as a indication
that the experimental parameters were sufficient to promote
growth of H. discus hannai within the published range for
this species. Growth in the experimental KX feed treatments
in this study was below the projected annual growth range
for H. discus hannai as reported by Lee (2004) and lower
than published growth rate for this species in experimental
studies (Table 8).
BW/SL ratio is a useful determinant of profitability in a
commercial species such as abalone (Naidoo et al. 2006),
where the final market product is the whole animal tissue
weight. Moreover, the BW/SL ratio gives an indication of the
level of ÔfatteningÕ achieved by on-growing feeds and as such
is a useful tool to collate the combined length and weight
achievements of a feed into a discernable parameter that
reflects commercial considerations. A commercially acceptable feed will ideally achieve high BW/SL ratios more so than
extreme growth in either biometric dimension (e.g. length
and weight).
The BW/SL ratio in this study showed that the highest
BW/SL ratio was achieved on the L. digitata treatment
(0.155 ± 0.001 g mm)1). This was a significantly higher BW/
SL ratio than that of the initial sample (0.108 ±
0.001 g mm)1) and was also significantly higher than the
Reference
Species
Interim feed type
Britz (1996b)
Guzman & Viana (1998)
Haliotis midae
Haliotis fulgens
Coote et al. (2000)
Shipton & Britz (2001)
Sales et al. (2003)
Macey & Coyne (2005)
Garcia-Esquivel et al.
(2007)
Zhang et al. (2008)
Haliotis laevigata
H. midae
H. midae
H. midae
H. fulgens
Plocamium corallorhiza
Artificial feed (abalone viscera
silage, fish meal &
soybean meal)
Experimental study feeds
Fish meal artificial feed
Artificial feed–reared abalone
Basal artificial feed
No interim feed mentioned
This study
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
Haliotis discus
hannai
H. discus hannai
Acclimation
period
3 months
75 days
22
1
16
3
2
days
month
months
weeks
weeks
Basal artificial feed
1 week
Laminaria digitata
2 weeks
Reference
Feed type
Mai (1998)
Mai et al. (2001)
Tan & Mai (2001a)
Tan & Mai (2001b)
Tan et al. (2001)
Tan et al. (2002b)
Park et al. (2008)1
Artificial feed
Artificial feed
Artificial feed
Artificial feed
Artificial feed
Artificial feed
Undaria pinnatifida
Laminaria japonica
Laminaria digitata
KX feeds
This study
Study
duration
(days)
Growth
(length)
(lm day)1)
Weight
gain
(% day)1)
100
112
120
112
112
112
180
–
66.4–76.0
38.66–59.60
62.3–86.6
67.4–86.9
36.87–55.07
100.0
0.74–0.88
1.27–1.34
0.39–0.49
0.48–1.22
0.76–1.24
0.37–0.58
1.35
58.0
22.0–26.0
0.56
0.14–0.23
84
Table 8 Comparative growth performance of Haliotis discus hannai in
experimental growth trials
KX, konjac glucomannan–xanthan gum.
Commercial-scale experimental study.
1
Table 9 Mean survival rates (%) of Haliotis discus hannai in previous and the current on-growing studies
Reference
Study
duration
(days)
Mercer et al. (1993)
Mai et al. (1995a)
Mai et al. (1995b)
Mai (1998)
Mai & Tan (2000)
Mai et al. (2001)
Tan et al. (2001)
Tan & Mai (2001a)
Tan & Mai (2001b)
Park et al. (2008)1
This Study
365
100
100
100
112
112
112
120
112
180
84
1
Length
(mm)
Weight
(g)
Stocking
parameters
(individuals tank)1)
Tank
volume
(cm3)
Survival
(%)
19.3 ± 0.10
0.817 ± 0.03
0.389
0.378 ± 0.02
0.23 ± 0.01
0.702 ± 0.02
0.145 ± 0.001
0.62 ± 0.02
1.18 ± 0.04
0.74 ± 0.01
2.2
2.79 ± 0.06
25
20
25
30
25
40
25
30
25
1667
15
5301
10 000
10 000
10 000
8000
19 600
8000
8000
8000
192 · 104
8400
84.0–95.0
87.5–98.3
92.0–98.7
86.7–96.7
88.0–100.0
85.8–94.2
94.7–100.0
75.0–83.3
94.7–100.0
94.5
91.1–100.0
–
–
16.11
10.92
15.45
18.65
16.41
24.5
25.89
±
±
±
±
±
0.10
0.10
0.03
0.18
0.04
± 0.18
Commercial-scale experimental study.
BW/SL ratio of all experimental KX feed treatments at the
end of the study. The BW/SL ratio of Diet A was not significantly different to the initial BW/SL ratio, and this was
the only experimental KX diet that showed no significant
increase in BW/SL ratio over the duration of the growth trial.
Although differences between KX feeds were non-significant,
trends showed that Diet C (0.119 ± 0.01 g mm)1) was the
best performing experimental KX diet in terms of the
BW/SL ratio increase of all novel feeds.
Survival in all treatments in this study was high and
L. digitata promoted maximum survival (100%) in this
study. The overall high survival rate (>91%) in all treatments
in this study may be an indication of the general suitability of
the KX feeds for abalone culture.
High survival rates have been reported for H. discus hannai
in previous studies (Table 9). The high percentage survival in
this study may also be linked to the husbandry protocols
maintained throughout the experimental period. Abalone
culturing success has been linked to a number of experi-
mental parameters including handling stress (Sales & Britz
2001), light intensity (Hahn 1989; Kim et al. 1997), water
quality (FAO, UNDP & Shallow Seafarming Institute 1990),
tank design and nutrition (Searle et al. 2006) and water
temperature (Britz et al. 1997). Frequent tank cleaning at
each feeding interval has also been attributed to survival
success with H. discus hannai (Mai et al. 1995b). Haliotis
discus hannai in this study were cultured within the recommended ranges for this species (FAO, UNDP & Shallow
Seafarming Institute 1990) with the exception of water temperature, which was maintained below the range outlined in
FAO, UNDP & Shallow Seafarming Institute (1990) but
above water temperature targets of previous studies (Mai
et al. 1995b; Park et al. 2008). The experimental system
utilized for this study entailed minimum handling of abalone
that were maintained in darkness during the growth trial.
Garcia-Esquivel et al. (2007) have demonstrated that Haliotis
fulgens can be best cultured at 20 C and 00 : 24 or 12 : 12
light : dark regimes.
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
The aim of this study was to determine the most appropriate
feed binder for further KX feed development for juvenile
H. discus hannai. Based on the overall lack of a significant
difference between KX treatments in this study, further diet
development was based on the trends observed between
treatments. In terms of FCE, SGR, BW/SL ratio and survival, trends showed that the use of DW did not positively
benefit KX feed performance. There are subtle, although
non-significant, indications that a reduced K : X ratio was
beneficial to overall feed performance.
Based on the results of this study, further feed development for abalone was conducted using the binder configuration of Diet C (SW 2% KX; 1 : 1). Overall, the results of
this study indicated that feed and growth performance of
juvenile H. discus hannai was better with feeding fresh
L. digitata, and therefore an optimized diet formulation will
be utilized in the next phase of KX diet development for
juvenile H. discus hannai (OÕMahoney 2009).
The observed ability of the KX-produced feeds to retain
structural integrity in SW is an indication of the potential for
this binder in aquatic feed production where water quality
issues are paramount. Despite the good growth rates that
may be achieved with some existing commercially available
abalone feeds, we have observed that such feeds can create
severe problems with water quality maintenance. Such
aspects negate the positive benefit of these existing feeds for
commercial use. An all-encompassing sustainable feed
development programme requires consideration of the environmental impact of the aquatic feeds in conjunction with
the input resources.
This study was conducted at the Aquaculture & Fisheries
Development Centre (AFDC), University College Cork. This
research was funded by Enterprise Ireland Commercialization Fund 2007–2008. The authors thank Chris OÕGrady of
Brandon Bay SeafoodÕs Ltd for the supply of abalone.
Thanks also to the staff of the AFDC for technical assistance.
Thanks to Prof. Ed. Morris for comments on the manuscript
and also to the reviewers for insightful contributions. This
study is dedicated to James OÕMahoney.
Alvarez-Manceñido, F., Landin, M. & Martı́nez-Pacheco, R. (2008)
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Aquaculture Nutrition 2011 Blackwell Publishing Ltd
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