AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA
ISSN Print: 2151-7517, ISSN Online: 2151-7525, doi:10.5251/abjna.2011.2.1.56.60
© 2011, ScienceHuβ, http://www.scihub.org/ABJNA
Health implications of harmful algal blooms in tank culture of catfish
Agatha A. Nwabueze
Department of Fisheries, Delta State University, Abraka,
Asaba, Campus, Asaba, Nigeria, E-mail: [email protected]
ABSTRACT
Health implications of harmful algal bloom in tank culture of Clarias gariepinus were investigated
to ascertain its possible effects on fish by application of commonly used organic manure for pond
fertilization.
Poultry droppings, cow dung and excess feeding were used to generate algal
blooms in tanks A, B and C respectively with tanks held in a static non-renewal bioassay and tank
D (control) in static renewal bioassay. Ten juvenile cat fish introduced into the tanks were fed
twice daily. Water samples were collected weekly from all tanks and analyzed by microscopy for
presence of algae and water quality parameters. Algal bloom was observed in tanks A and B
while blooms were not found in Tanks C and D. Algal species identified were Anabaena, Volvox,
Phacus, Euglena, Spirogyra, Chlamydomonas, Synedra, Mallomones, Oscillatoria, Ceratium,
Dinoflagellates, Cladophora, and Microcystis. Similar species with significantly higher (P≥ 0.05)
number of algae/ ml was observed in tanks A and B than in C and D. The duo of Anabaena and
Chlamydomonas blooms had the highest number of algae/ ml in tanks A and B respectively. Fish
kills and algae die off were observed in tanks A and B as well as oxygen depletion also in tank C
except in control. Dissolved oxygen level was significantly reduced (P ≥0.05) in tanks A and B
when compared tanks C and D. Turbidity levels followed an increasing sequence of tanks D < C
< A < B. Temperature and pH in treatment tanks were not significantly different from control. This
study has shown that using poultry droppings for pond fertilization can encourage harmful algal
bloom. There is a need to assess and monitor algal growth in tank culture of fish to know the
species of algae in water samples and be able to estimate the algal density which is important to
reduce impact of algal bloom in water bodies.
Keywords: Health implications, harmful algal bloom, tank culture, catfish.
INTRODUCTION
Algae are naturally occurring microscopic plants that
are usually aquatic, unicellular and lack true stems,
roots and leaves (Bowman et al., 2010). Algae are a
diverse group of simple, typically autotrophic
organisms ranging from unicellular to multi cellular
forms (Wikipedia, 2010). Algae are natural fish food
and its density determines the greenness of pond
water and primary productivity (Alphonse, 1997). An
algal bloom is a rapid increase or accumulation in the
number of algal cells such that the algae dominate
the planktonic community (Bowman et al., 2010).
According to Lathrop et al. (1998) and Diersing
(2009), fresh water algal bloom results from
excessive nutrients, particularly phosphorus, which
originates from fertilizers that are applied to land for
agricultural or recreational purposes and enter
watersheds through run-off. Additional causes of
algal bloom have been documented (Anderson et al.,
2002). Problems associated with algal bloom include
algae die off which lead to oxygen depletion of water
column (hypoxia or anoxia) from cellular respiration
and bacterial degradation (Mellergaard and Nielson,
1987). Chorus and Bartram (1999) also noted that
when algae die off and decompose, carbon dioxide
and nutrients are released back into the pond for the
next generation of plants. Harmful algal bloom can
occur when certain types of microscopic algae grow
quickly in water forming visible patches. This often
times, may contain cyanobacteria because most
species of algae are not harmful and serve as the
energy producers at the base of the food web (Falk et
al. 2000). Cyanobacteria, also known as blue-green
algae are actually bacteria, not algae, since their
genetic material is not organized in a membranebound nucleus as found in true algae which have true
nucleus (Agriculture & Agri-food, 2007). However,
algae and cyanobacteria occur together naturally in
surface waters where both can undergo blooms.
Blue-green algae have been identified as having
ability to produce highly potent toxins referred to as
cyanotoxins (Anderson et al., 2000). Anderson et al
(2006) observed that harmful algal bloom constitute
serious threat to coastal resources, causing impacts
ranging from contamination of sea food products with
potent toxins to mortalities of wild and farmed fish
and other marine animals. Other problems
Agric. Biol. J. N. Am., 2011, 2(1): 56-60
associated with algal blooms are objectionable odor
and tastes, poor aesthetic value, large fluctuation in
pH, clogging of fish gills leading to fish kill, poisoning
of fish, livestock and humans who drink or bath in
ponds with algal bloom.
The original weight of the oven-dried filter paper
which was obtained before filtration was subtracted
from the weight of the desiccated filter paper plus
samples. The value obtained was taken as the value
of suspended solids in the sample. Turbidity was
determined using a secchi disk. Algae were collected
by horizontal tows with a 55µm-1 mesh size bolting
silk plankton net at a depth of 25 cm according to
APHA (1992). Samples were preserved in 4%
formalin. Samples were decanted to remove the
supernatant. Fresh clean water was added to the
sediment and centrifuged. The supernatant was
again decanted and fresh water added to make up to
10 ml in the centrifuge tube which was agitated and 1
ml of subsample pipette onto the counting chamber
(Neubauer
haemacytometer,
Marienfeld)
for
quantitative estimation of species of algae by
examining fractions of each sample under the
microscope. Algae were identified to generic level as
much as possible and enumerated by binocular
microscopy (x 100 magnification) using keys
according to Willoughby (1976) and Green
Water/Cyano Laboratories (2007). The number of
algae/ml was calculated according to a formula by
Boyd and Lichtkoppler (1979).
Rearing of catfish in tank is rapidly developing in
Nigeria and poultry dropping is commonly used as
manure for fertilization. However, many interested
fish farmers lack the basic knowledge of algal bloom
and its application in tank culture of fish. To maintain
productivity of tank culture, algal density must be
monitored within favorable ranges and species of
algae identified to prevent algal blooms, particularly
harmful blooms which may be deleterious to fish
health and by implication, health of fish consumers.
This study investigates the health implications of
harmful algal blooms in tank culture of catfish.
MATERIALS AND METHODS
The study which lasted six months in 2008 was
conducted in the Department of Fisheries, Delta
State University, Abraka, Asaba Campus. Four
experimental concrete tanks measuring 6ft x 4ft x 4ft
were used. Each tank contained borehole water to
2.5ft level. Two jute sacs of four kg each of poultry
droppings and cow dung as well as excess feeds
were used to generate algal bloom in tanks A, B and
C respectively in the culture of Clarias gariepinus,
catfish held in static non-renewal bioassay systems.
Tank C received excess feeds while the fourth (tank
D) was held in a static renewal bioassay and served
as the control. All four tanks were allowed to stand for
two weeks before the introduction of ten juvenile C.
gariepinus (averaging 18.4 + 0.05 cm, total length
and 133.1 + 0.14 g, weight) in each of the tanks.
Supplementary feeding of fish in all four tanks was
carried out twice daily (10.00 am and 6.00 pm) with
commercially available feeds at 4% body weight for
eight weeks. The experiment was replicated twice of
eight weeks each. Water samples from the four tanks
were collected weekly and analysis. Temperature
was determined in-situ with mercury –in-glass
thermometer. Dissolved oxygen was determined by
oxygen meter (LabTech., England) while pH was
determined using an electric pH model PHS-25
(Techmel and Techmel, USA) pH meter. The meter
was standardized with solution of known pH and
meter adjusted accordingly before use. For total
suspended solids, gravimetric method was used.
Briefly, 100 ml of water samples were filtered through
dried weighted Whatman no.4 filter paper. The filter
0
was oven-dried at a temperature of 105 C and stored
in a desiccator until a constant weight was obtained.
Number of plankton (algae)/ml
=
T x 1000
AN x Vol. of concentrate in ml/Vol. of sample
Where:
T = total number of algae counted
A = area of grid in mm2
N = number of grid counted
1000 = area of counting chamber in mm2
Skin scrapings of samples of catfish in each tank were
examined by microscopy for presence of algae. Data
obtained were subjected to analysis of variance (ANOVA)
at P≤0.05 level of significance. While the significant means
were separated with the Duncan’s multiple range test
(DMRT) using SAS (1996).
RESULTS
Algal bloom was observed in experimental tanks A
and B with poultry droppings and cow dung organic
manure respectively. Algae without bloom were found
in Tanks C and D (Control). Algal species identified
were Anabaena, Volvox, Phacus, Euglena,
Spirogyra, Chlamydomonas, Synedra, Mallomones,
Oscillatoria, Ceratium, Dinoflagellates, Cladophora,
and Microcystis colony. There was also unidentified
plankton in some of the samples. Table 1 shows
algae species found in the treatment and control
tanks. Similar species with high number of algae/ ml
were found in tank culture with poultry droppings and
cow dung. This was significantly higher (P≥ 0.05)
57
Agric. Biol. J. N. Am., 2011, 2(1): 56-60
than species and number of algae/ ml in tanks C and
D (Control). Blooms in Anabaena followed by
Chlamydomonas species of algae were observed.
The duo having the highest number of algae/ ml in
tanks with poultry droppings and cow dung manure.
The number of Anabaena was higher in poultry
droppings while Chlamydomonas was higher in cow
dung manure. A progressive increase in algal number
was observed in all tanks during the study. Mean
weekly abundance of algae species/ ml in the culture
tanks are presented in tables 2 and 3.Objectionable
odor was perceived from tanks A and B which also
had fish kills. Three (33.3%) and two (20%) of ten fish
each in tanks A and B respectively were found
th
th
floating on water surface in the 6 and 7 weeks of
the study. Some fish samples in tanks A and B also
had their gills clogged with green scum of algae
some of which were found floating on the surface of
the tank water. The skin of some of the fish samples
examined had patches of greenish algae. Algae die
off were observed on the surface around the inside
walls of tanks A and B. Skin scrapings from fish
samples shows the presence of algal cells on the
skin surface.
Analysis of water quality parameters shows that
oxygen depletion occurred in the non-renewal static
bioassay tanks A, B and C while tank D with renewal
bioassay system had higher levels of oxygen.
Dissolved oxygen level was significantly reduced (P
≥0.05) in tanks A and B with poultry droppings and
cow dung manure but not significantly reduced (P≤
0.05) in tank C when compared with the control.
Water turbidity was highest in the cow dung
treatment tank B. Turbidity levels followed an
increasing sequence of tanks D (control) < C < A < B
.Turbidity levels were however not significantly higher
(P ≤ 0.05) in tanks A and B than in tanks C and D.
Secchi disk depth measurement shows that tank B
had a depth of 0.06m, followed by tank A with 0.11m,
tank C, 0.29m and tank D, 0.58m. A mean pH value
of 8.2 and 8.7 was observed in tanks A and B
respectively while pH in tank C had a mean of 7.2
and in tank D it was 6.8. Temperature remained fairly
0
0
constant with 29.4 C to 29.9 C range. Table 4 shows
the mean values of water quality parameters
determined.
of study. The growth of algae was faster in the tank
with poultry droppings than the tank with cow dung.
Ajayi (2006) noted that poultry droppings generated
the most productive algal blooms. Blooms of
Anabaena found in tank A with poultry droppings and
Chlamydomonas in tank B with cow dung show a
possibility of harmful algal bloom, especially in fish
culture using poultry droppings for pond fertilization.
Wikipedia (2010), reported that only one or few
species of phytoplankton algae are normally involved
in blooms. Anabaena and Chlamydomonas had the
highest growth in number/ml among thirteen algal
species found in water samples. According to
Anderson (1997) a great variety of algae species can
be found in water samples with algal bloom some of
which may be harmful. The algal species found
include blue-green algae (cyanobacteria) such as
Anabaena, Microcystis and Oscillatoria. These bluegreen algae especially Anabaena have been reported
to be capable of causing negative impacts to other
organisms via production of natural potent toxins.
Health Link (2005) reported that blue-green algae
can be poisonous if swallowed in water by wildlife,
livestock and humans. Although toxicity testing of
harmful algal bloom was not done, the occurrence of
harmful algal bloom in one of the treatment tanks is
enough reason to be cautious in the application and
use of organic manure in tank culture of systems.
Agriculture and Agri- Food (2007) reported that it is
difficult to a certain when blue-green algae bloom
produce toxins and so it is better to avoid them
completely. Treatment tanks A and B had
objectionable odor probably arising from the manure
used and the presence of algae which contribute
distinctive odors and tastes to water such as
Anabaena, Volvox, Mallomones, Synedra and
Ceratium (Haine et al., 2001). Fish gills were
observed to be clogged with scum of algae from tank
surface water. Skin scrapings also showed presence
of algal cells on fish. The clogging of fish gills may
have resulted in obstruction of gaseous exchange
coupled with low level of oxygen in the tanks due to
the algae die off and subsequent bacteria
degradation. These facts probably contributed to the
fish kill observed in the sixth and seventh week of the
experiment. Algae die off have been reported to
increase organic matter in the water necessitating
degradation by aerobic bacteria which further
depletes the oxygen content of the water. Oxygen
depletion alone has also been known to be capable
of causing fish kill (Connell and Miller, 1984).
DISCUSSION
Algal bloom observed in experimental tanks with
poultry droppings and cow dung organic manure is
an evidence of excess nutrients in the tanks. The
growth of algae was not delayed as results obtained
showed a progressive algal growth during the period
58
Agric. Biol. J. N. Am., 2011, 2(1): 56-60
Table 1: Algal species in treatment and control tanks.
S/No
Tank A
Tank B
Poultry Droppings
Cow Dung
Tank C
(Excess Feed)
Tank D
(Control)
1
Anabaena
Anabaena
2
3
4
Volvox
Phacus
Euglena
Volvox
Phacus
Euglena
Volvox
Euglena
Euglena
5
6
7
Spirogyra
Chlamydomonas
Synedra
Spirogyra
Chlamydomonas
Synedra
Spirogyra
Chlamydomonas
-
Spirogyra
Chlamydomonas
-
8
9
10
Mallomones
Oscillatoria
Ceratium
Mallomones
Oscillatoria
Ceratium
Oscillatoria
Ceratium
11
12
13
Dinoflagellate
Cladophora
Microcystis
Dinoflagellate
Cladophora
Microcystis
Dinoflagellate
Cladophora
-
-
-
Cladophora
-
Source: Field survey (2008).
Table 2: Mean weekly abundance of algae species in treatment tanks.
S/No
Algae Species
Week 1
Week 2
Week 3
Week 4
Week 6
Week 7
Week 8
1
Anabaena
2.7
3.0
3.2
4.5
6.1
7.8
8.3
8.6
5.5
2
3
Volvox
Phacus
2.1
2.0
2.3
2.5
2.8
2.9
3.3
3.0
3.7
3.3
4.0
4.6
4.9
4.8
5.5
5.6
3.6
3.6
4
Euglena
2.3
2.6
2.8
3.1
3.4
5.0
5.1
5.3
3.7
5
Spirogyra
2.4
2.5
3.0
3.2
3.5
4.2
4.7
5.2
3.6
6
Chlamydomonas
3.0
3.2
3.3
4.2
5.8
6.4
7.3
8.1
5.2
7
8
Synedra
Mallomones
2.6
2.3
2.7
2.6
2.9
2.8
3.4
2.9
4.1
3.3
4.5
3.7
4.9
4.0
5.2
4.4
3.8
3.3
9
Oscillatoria
1.9
2.2
2.4
2.5
2.8
3.0
3.6
3.8
2.8
10
Ceratium
1.6
1.8
2.1
2.5
3.1
3.4
3.6
4.0
2.8
11
Dinoflagellate
2.0
2.7
2.8
2.9
3.0
3.2
3.5
3.9
3.0
12
13
Cladophora
Microcystis
1.8
2.0
2.4
2.2
2.7
2.5
3.0
2.6
3.5
2.9
3.6
3.6
3.8
4.1
4.2
4.2
3.1
3.0
Source: Field
survey
Week 5
Total
(2008).
Table 3. Mean weekly abundance of algae species in control tank.
S/No
Algae Species
Week 1
Week 2
Week 3
Week 4
Week 5
Week 6
1
Euglena
1.2
1.4
1.5
1.7
2.0
2.3
2
Spirogyra
1.5
1.8
2.1
2.2
2.4
2.6
3
Chlamydomonas
1.4
1.7
1.8
1.9
2.3
2.4
4
Cladophora
1.3
1.3
1.6
1.8
1.9
2.0
Source: Field survey (2008).
Table 4: Mean values of water quality parameters in treatment and control tanks.
S/No
Water Quality Parameter
Tank A
Tank B
(poultry droppings)
(Cow dung)
1.
Dissolved oxygen (mg/l)
2.2
2.7
2.
Turbidity (secchi
0.11
0.06
Depth, m)
3.
pH
8.7
8.2
4.
Temperature(0C)
29.9
29.4
5.
Suspended solids(mg/l)
112.6
101.3
Source: Field survey (2008).
59
Week 7
2.5
2.7
2.6
2.2
Week 8
2.8
2.9
2.7
2.4
Tank C
(excess feed)
3.1
0.29
7.2
29.8
94.5
Total
1.9
2.3
2.1
1.8
Tank D
(control)
4.4
0.58
6.8
29.6
67.7
Agric. Biol. J. N. Am., 2011, 2(1): 56-60
The water samples analyzed clearly showed that there
was oxygen depletion in tanks A and B. Tank C also
had reduced oxygen content probably due to the nonrenewal bioassay system, which did not provide for
improvement in the oxygen content of the tank water.
Tank D with renewal of bioassay system however, had
oxygen content with optimal ranges for fish growth.
Turbidity levels were higher in the treatment tanks than
in the control. The greenish color impacted in the tank
water by the algal bloom is likely responsible for the
higher turbidity observed in the treatment tanks. Similar
reports also show that greenness of the algal bloom
signifies density of algae or high algal turbidity
(Alphonse, 1997). High algal turbidity has been reported
to reduce the penetration of sunlight into water bodies
(NLWRA, 2008). Increased levels of pH observed
corroborate earlier studies of Radke (2008), who noted
that photosynthetic consumption of CO2,especially in
algal bloom causes an increase in the level of pH.
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This study has shown that tank culture of catfish using
poultry droppings and cow dung as manure for pond
fertilization could result in harmful algal bloom. In view
of the possible health implications of harmful algal
bloom in fish culture systems, there is a need to assess
and monitor algal growth in tank culture of fish to know
the species of algae present in water samples and to be
able to estimate the algal density which is important to
reduce impact of algal bloom and oxygen depletion in
water bodies.
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