PARTICULATE AND FILTER FEEDING IN THE THREADFIN SHAD,
DOROSOMA PETENENSE (GUNTHER), AT DIFFERENT LIGHT INTENSITIES
by
Stephen Howard Holanov
A Thesis Submitted to the Faculty of the
SCHOOL OF RENEWABLE NATURAL RESOURCES'
In Partial Fulfillment of the Requirements
For the Degree of
. MASTER OF SCIENCE
WITH A MAJOR IN FISHERIES SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 7 7
'
-
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of re­
quirements for an advanced degree at The University of Arizona and is
deposited in the University Library to be made available to borrowers
under rules of the Library.
Brief quotations form this thesis are allowable without special
permission, provided that accurate acknowledgment of source is made.
Requests for permission for extended quotation from or reproduction of
this manuscript in whole or in part may be granted by the head of the
major department or the Dean of the Graduate College when in his judg­
ment the proposed use of the material.is in the interests of scholar­
ship o In all other instancess however, permission must be obtained
from the author.
SIGNED
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
c
J. G. TASH
Associate Professor
of Fisheries
ACKNOWLEDGMENTS
I am extremely grateful to Dr, Jerry C, Tash for his efforts
in teaching scientific method and writing ability, which along with his
advice and encouragement, made this study possible,
1 also thank Mr,
Charles D, Ziebell and Dr, Donald A, Thomson for their suggestions while
conducting the research and for reviewing this manuscript,
Jim Brooks, Tom McMahon/, Dr, Michael Saiki, and Tom Satterthwaite are acknowledged for their help in the field, as well as Dave
Kennedy for his advice.
This study was supported.by the Arizona Cooperative Fishery
Research Unit,
TABLE OF CONTENTS
Page
LIST OF TABLES .
.........
LIST OF ILLUSTRATIONS
ABSTRACT . . . . .
INTRODUCTION .
v
. . . . . . . . . . . . . . . . . . . . . .
vi
. . . . . . . . .. . . . . . . . . . . . . . . .
vii
........
METHODS AND MATERIALS
. . . . . . . . . . . . . . . . . . . . .
1
. . . . . . . . . . . . . . . . . . . . . .
2
Testing Room and Aquarium . . . . . . . . . . . . . . . .
Experimental Lighting . . . . ............ . . . . . . .
. Light Measurements . . . . . . . . . ........ . . . . . .
Feeding Apparatus
................. . .
Fish H a n d l i n g .................
.
Filter Feeding Experiments . . . . . . . . . . . . . . . .
Brine Shrimp Nauplii (Artemia sp.) . . . . . . . . .
Phytoplankton . . . . . . . . . . . . . . ..........
Particulate Feeding Experiments . . . . . . . . ........
RESULTS
. .
Filter Feeding Experiments . . .
Brine Shrimp Nauplii . . .
Phytoplankton . . . . . . .
Particulate Feeding Experiments
DISCUSSION . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
2
2
2
3
3
4
5
5
6
7
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7
9
11
13
17
LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . .
iv
22
LIST OF TABLES
Table
Page
1. Average distances between gill rakers at mid-point of
eight thread fin shad . . . , . „„ . . . . . . '. . . . . . . „
2.
3.
4.
The percentage of threadfin shad that filter fed on
brine shrimp nauplii at four different light
intensities . . . . . . . . . . . . . . . . . . . . . . . . .
Types and dimensions of the phytoplanktons used in the
filter feeding experiments
10
.
The percentage of threadfin shad that filter fed on
varying concentrations of phytoplankton at two light
intensities . . . . . . . . . . . .
. . . . . . . .
5. The average number of adult brine shrimp eaten in
five experiments (with five fish per experiment) at
each of six light intensities. . . . ........ . . . .
v
8
. . . .
12
14
16
LIST OF ILLUSTRATIONS
Figure
1.
Comparison of the filter feeding (solid line) and
particulate feeding (broken line) abilities of thread
fin shad to light intensities in the field . . . . .
ABSTRACT
Previous workers inferred from stomach analyses that threadfin
shad (Dorosoma petenense) ate plankton.by both filter and particulate
feeding.
These inferences were confirmed in this Study by laboratory
experiments in which both types of feeding were observed.
Threadfin shad consumed relatively small food particles
(< 0.39 mm) by filtration, while larger prey (7.5 mm) were eaten
individually.
Threadfin shad were able to filter feed on small foods (brine
shrimp nauplii and phytoplankton) at all light intensities from 0 to
9 x l.Ol fL.
These data indicate that under natural conditions shad can
filter feed at any time of the 24 hr period if food conditions are
sufficient to trigger feeding. ' Filter feeding is probably triggered
by chemoreception rather than vision.
The particulate feeding rate decreased as light intensity
decreased, reaching a minimum between 9 x 10 4 and 9 x 10 ^ fL.
From these data it is inferred that particulate feeding is a visual
process in this species, requiring intensities equivalent to bright
moonlight or greater.
Filter and particulate feeding abilities allow threadfin shad
to consume most of the different types of plankton and to change their
diet with seasonal changes in fhe composition of the plankton.
INTRODUCTION
Most planktivorous fish feed by attacking and swallowing
individual prey (particulate feeding), while a few (filter feeders)
strain numerous small food particles from the water with their gill
rakers (Brooks, 1968)•
Miller (1961) concluded from stomach analyses
that threadfin shad probably feed both by filter and by particulate
feeding, a phenomenon that has been observed in only a few other
species of fish (Leong and O'Connell, 1969; Loukashkin, 1970; Volkova,
1973; Janssen, 1976).
Until this study, no one had actually observed
threadfin shad filter feeding, and the only observations of particulate.
feeding in threadfin shad were made by Gerdes and McConnell (1963),
who.watched them eat individual cladocerans*
(
Although light intensity has been found to be closely correlated
to feeding in many particulate feeding planktivores (Woodhead, 1966)
there has been only one other study of the effect of light on a filter
feeding species of fish (Volkova, 1973)„
No one has studied the effects
of different light intensities on the feeding of threadfin shade
This study was done to gain more data on the interactions of
light and feeding in planktivorous fish, and to confirm the occurrence
of filter and particulate feeding in threadfin shad, to describe these
feeding behaviors, and to describe these feeding activities at different
light intensities.
,
1
METHODS AND MATERIALS
Testing Room and Aquarium
Experiments were conducted in an aquarium inside a light-tight
O
testing room. The room was a wooden frame9 2 . 1 m 9 covered with 6 mil
\ u%'
o
black plastic.
'
,
. »
/. ,
^
.
. .
The aquarium (0.6 m x 0.6 m x 1.9 m) held 600 1 of water.
To produce a relatively uniform light field, the top of the aquarium
was covered with a sheet of translucent white plastic and the inside
walls and bottom of the aquarium were covered with opaque white plastic
panels.
Four observation windows 9 10 cm x 10 cm? were cut in the
plastic along the front (long axis) of the aquarium.
A sheet of
black plastic was hung in front of the aquarium from the ceiling to
below the bottom of the aquarium9 with holes matching the observation
windows, which prevented light from the aquarium from illuminating the
observer.
Experimental Lighting
Lighting was from two 40 W "daylight" fluorescent bulbs which
gave a relatively close spectral match to sunlight (Withrow and Withrow,
1956)»
For small changes in light intensity, the fixture was raised
and lowered oh pulleys. Large changes were made by covering the bottom
of the fixture with varying amounts of black plastic.
Light Measurements
Light was measured with a hand-crafted light-meter (Holanov,
in manuscript) in which the 931A photomultiplier tube (light sensitive
2
element) was calibrated with a Weston 756 Sunlight Illumination Meter*
The range of the light-meter was 6 x 10
2
to 10
-6
foot-lamberts (fL)*
Measurements in the field and laboratory of horizontally reflected
light were made just under the surface of the water•
Field measurements
were made under sunlight, full and partial moonlight9 and starlight,
with clear skies, Measurements in foot-lamberts are considered
equivalent to those in foot-candles for comparison to other studies
(Hunterj 1968),
Feeding Apparatus
Foods were added to the experimental aquarium via vinyl hoses
13 mm in diameter,
A single; hose led from a funnel to a Y » Two other
hoses fe9m the Y led to the back comers of the aquarium and ended
behind pieces of white plastic (10 cm wide) placed diagonally across
the comers.
The diagonals extended from 3 cm off the bottom to
within 3 cm of the surface of the water.
At the beginning of an
experimentj food suspended in water was poured into the funnel and
flowed by gravity into the corners, Air released in the corners caused
water to flow upward) mix with the food 9 and dispersed.the food through­
out the aquarium in a few seconds,
The continuous movement of the water
prevented food from settling on the bottom.
Fish Handling
About 200 threadfin shad', 7,0 cm to 14.1 cm total length
(x = 10,5 cm) were obtained from Canyon Lake (80 km east of Phoenix9 Az)•
4
. ,
In the laboratory 9 shad were held prior to anti -between', experi­
ments in galvanized horsetroughs (0„5 m x 0*5 m x 1 *2-1,5 m) holding
about 400 1,
Up to 40 fish were held in a horsetrough at a time.
Between experiments 9 fish were usually fed frozen brine shrimp once per
dayo
The water in .the horsetroughs was ,changed weeklys aerated contin­
uously 5 and temperatures kept at 20 to 23 C,
The laboratory outside
the testing room was illuminated with two 40 W fluorescent lights on
a 12 hr light/dark timer..
Fish were deprived of food for 22 to 26 hr before testing.
The
water in the experimental aquarium was changed before each experiment
and adjusted to within 2 C of the horsetrough from which the fish were
selected.
Five.shad were selected randomly from a horsetrough)
2 to 5 cm variation in length between fish per experiment.
with
The behavior
of the five fish in the aquarium was observed for 5 min after their
introduction, and abnormally behaving fish were replaced.
The air
in the comers was turned on and the fish were acclimated for 2 hr
before testing.
After being used in an experiment, fish were not
retested for at least a week, and no fish were tested more than threetimes o
Filter Feeding Experiments
The minimum effective size range of particles possible for shad
to filter was determined by measuring the distances between gill rakers
for eight fish.
Measurements were made at
on the lower limb of the.first gill arch.
on each fish and the average was computed.
the mid-point of the rakers
Six measurements were made
Brine Shrimp Nauplii (Artemia sp.)
Six experiments were conducted at different light levels,
1
one at 9 x 10 , 9 x 10
-1
Q
, and 9 x 10 ^ fL , and three at 0 fL using.
brine shrimp nauplii (0.34-0.60 mm, x = 0.39 mm length) for food.
Fifteen ml of nauplii, concentrated with a centrifuge, were mixed with
one 1 of water which was then flushed with two 1 of water into the
experimental aquarium after the test fish had been acclimated.
The con
centration of nauplii in the test aquarium was about 1000/1 , measured
by counts from samples of water taken after two of the experiments.
Fish, were removed from,the test aquarium 10 min after the
introduction of the nauplii and placed in 10% formalin.
Digestive
tracts from these fish were examined and, the fish were divided into: two
groups (depending on the total number of nauplii in the gill rakers,
esophagus, gizzard, and intestine): (1) those with 0 to 25 nauplii were
considered not to have fed since these few nauplii could have been
ingested incidentally by respiratory movements; and, (2) those with
26 or more nauplii were considered to have fed.
Phytoplankton
Three experiments were conducted at 3 x 10
0
fL and four at 0 fL
A mixture of phytoplankton species was obtained from an outdoor tank
and filtered through a net with a mesh size of 76 /U to remove zooplankton and larger particles.
At the start of an experiment, 75 1 of
filtered water containing phytoplankton was pumped for 10 min into the
experimental aquarium containing the acclimated fish.
The fish were
removed 1 hr after starting the pump and processed as in the brine
.
'shrimp experiments •
'
6
The digestive -tracts were examined . at 15 X; when
masses of green algae were seen, feeding was assumed to have occurred,
Samples of water were taken from the aquarium after experiments•
Phytoplankton were identified using the keys in Thompson (1959)„
Concentrations, were estimated by averaging 10 counts of the number of
plankters in 2.57 mm
in a Sedgewick-Rafter Cell under 100 X.
Particulate Feeding Experiments
Five experiments were conducted at each of these six light
levels: 9 x 101 , 9 x lO-1, 9 X 1(T3 , 9 x IQ-4, 9 x 10-5, and 0 fL.
In each experiment', ; 300 active adult brine shrimp (3.5-10.0 mm, x = 7.3
mm in length) were flushed with two 1 of water into the aquarium contain­
ing five acclimated fish.
ferred to a horsetrough.
After TO min, the fish were removed and trans­
The brine shrimp remaining in the aquarium ■
were counted and subtracted from 300 to find the number eaten by the
fish.
RESULTS
In preliminary experiments, I observed filter and particulate
feeding by threadfin shad,
Filter feeding occurred when relatively
small food particles were used and particulate feeding took place when
larger foods were offered•
Phytoplankton and brine shrimp nauplii were used in the filter
feeding experiments because these food particles were smaller than the
maximum size (1 mm) that elicited filter rather than particulate
feeding in northern anchovies (Engraulis mordax) and Pacific sardines
(Sardinops caerula) recorded by Leong and O ’Connell (1969) arid Loukashkin
(1970)o Adult brine shrimp were used in the particulate feeding exper­
iments because northern anchovies and Pacific sardines ate them indivi­
dually «> Also, adult brine shrimp are in the upper size range of foods
found in stomachs of threadfin shad (Miller, 1961),
Filter Feeding Experiments
Measurements were made of the distances between the gill rakers
to determine the minimum size of particles threadfin shad can filter.
The distance at the. mid-point between gill rakers in shad (8.0-14.1 cm
total length) averaged from 26 to 39 /I (Table 1).
Particles smaller
than these dimensions may be retained if trapped in groups or in spaces
between gill rakers that are already blocked (Miller, 1961).
Threadfin
shad add more gill rakers with growth so that the spacing of the rakers
may not vary directly with length (Miller, 1963).
8
Table 1.
Average distances between gill rakers at mid~point of eight
threadfin shad.
Total Length (cm)
Average Distance Between
Gill Rakers (jum)a
8.0
26
9.2
27
9.9
32
10.6
33
10.8
34
10.8
39
12.0
33
14.1
35
Each distance is the average of six measurements for each
fish.
9
Brine Shrimp Nauplii
Experiments with brine shrimp nauplii were conducted in light
intensities.of 9 x ,10**"s 9 x 10~\ 9 x 10^3, and 0 £L»
Before the
addition of food to the experimental aquarium, all five fish were usually
swimming in compact groups around the walls of the aquarium in a clock­
wise direction.
This behavior was maintained for 2 to 3 min after the
brine shrimp nauplii were added and before filter feeding began„
Once
filter feeding began, the groups dispersed and each shad moved randomly,
Filter feeding continued during the remainder of the 10 min period until
the fish were removed.
The fish did not ingest individual nauplii while
filter feeding, but filtered continuously by opening and closing their
mouths about two times per sec. with the opercula flaring further outward
than during respiration.
Filter feeding behavior in the threadfin shad
was similar to that reported for the gizzard shad (IX cepedianum) by
Drenner and O ’Brien (1976) and Atlantic menhaden (Brevoortia tyrannus)
by Durbin and Durbin (1975),
The percent occurrences of filter feeding by shad on brine
shrimp nauplii at different light intensities are given in Table 2,
All
fish fed at all light intensities tested except one (test number 4 at
0 fL); however, I could not detect any behavioral or external physical
abnormalities to indicate why it did not feed,
The filter feeding rate was high enough at all light levels
during the 10 min feeding time to fill the esophagi, gizzards, and in
some, even the pharyngeal organs of the shad.
Counts that were made
of the nauplii eaten by each of 10 shad ranged from 100 to 4000 per
10
Table 2.
The percentage of threadfin shad that filter fed on brine
shrimp nauplii at four different light intensities.
Experiment3"
Light Intensity
in Foot-Lamberts
1
2
9 x 101
—1
9 x 10
3
9 x 10
4
0
80
5
0
100
6
0
100
-3
aFive fish in each experiment.
Percent Occurrence
of Filter Feeding
100
100
100
11
shade
Volumetric estimates were made of the nauplii eaten by each
of these 10 shad; these volumes were then compared to the individual
food volumes for each of the other fish in which.no counts were made.
The results of this comparison indicated that most of the shad had con­
sumed between 100 and 1000 nauplii.
Phytoplankton
Since the experiments using nauplii showed that light intensity
had little effect on filter feeding9 it was unnecessary to conduct
experiments with phytoplankton with gradations;of light; these experiments were conducted only in bright light (3.x 10
fL)s and in darkness
(0 fL)e
The kinds and sizes of phytoplankton used in the experiments are
.
listed in Table.-;3; most of the individual plankters were 20 to 50 fx in
their largest dimension•
Each experiment with phytoplankton lasted 60 min.
After a 2 hr
acclimation period for the shad, phytoplankton was introduced for 10 min.
The addition of the phytoplankton to the experimental aquarium colored
the water green. /-The onset/ of filter feeding occurred 3 to 8 min after
the beginning of the phytoplankton introduction, and -then continued for
30 to 40 min.
After the experiments, the algae in most of the fish
filled the lumens of the gizzards, the upper 5 to 10 mm of the intes­
tines, and some of the intestinal caecae.
Little algae were found in
the pharyngeal organs and esophagi, probably because algae had passed
completely through these organs and out of them during the long period
12
Table 3.
Types and dimensions of the phytoplanktons used in the filter
feeding experiments.
Phytoplankton
Dimensions (pm)
Scenedesmus sp.
15 x 25
Miractinium sp.
55
Golenkinia sp.
40
Closterium sp.
Diatoms;
Unidentified
3 x 70
10 x 40
5to 50
13
of time between when the fish stopped feeding9 and when the fish were
removed at the end of the experiments®
The results of the filter feeding experiments using phytoplankrton are shown in Table 4,
In the three experiments at 3 x lO^fL, 14
out of the 15 fish used contained visible concentrations of algae in
their digestive tracts«
In the four experiments at 0 fL, 18 put of 20
fish used fed.
Particulate Feeding Experiments
Particulate feeding experiments on brine shrimp were conducted
at light levels of 9 x 10^, 9 x l o \
0 fL,
9 x 10
9 x lO""'^, 9 x 10
and
Before the addition of food to the experimental aquarium, the
shad s^am in groups around the aquarium as previously described for fil­
ter feeding.
After the introduction of the shrimp, some of the test
fish maintained these same swimming patterns while feeding, but most
dispersed and fed'randomly.
The shad ate individual brine shrimp by
moving very near to a shrimp and then.quickly opening and closing its
mouth to ingest it.
The feeding behavior was similar to the particulate
feeding behavior previously described for the anchovy by Leong and
0 ?Connell (1969), the alewife (Alosa pseudoharengus) by Janssen (1976),
and the herring"(Clupea harengus) by Blaxter (1966),
The average numbers of brine shrimp eaten by five groups of five
fish at each of 6 different light levels are shown in Table 5,
Most of
the 300 brine shrimp introduced at the start of each experiment were
eaten in every experiment at light levels of 9x10
1
and 9x10
_T
fL,
At
these light levels, the shad fed immediately upon the introduction of the
14
Table 4.
Experiment
The percentage of threadfin shad that filter fed on varying
concentrations of phytoplanktoh at two light intensities.
Light Intensity
in Foot-Lamberts
1
3 x 10
2
3
Food Concentration
(organisms/ml)
0
Percent Occurrence
of Filter Feeding
4,200
80
3 x 10°
3,700
100
3 x 10°
4,700
100
4
O'
2,500
■
-80
5
0
2,800
100
6
0
3,100 .
100
7
0
aFive fish in each experiment.
12,000
80
15
shrimp into the test aquarium, usually consuming most of them in less
than 2 min; only those hidden in corners or on the bottom of the ' ; .
aquarium were not eaten.
Feeding at light intensities of 9 x 10™^ and 9 x 1;0~^ fL did not
start until 2 to 3 min after introduction of the shrimp, then feeding
continued throughout the experiment at a lower rate than in the higher
light intensities.
The feeding rate at the light
2.4 brine shrimp per experiment.
The
intensity of 9 x 10~^ fL averaged
shad swam in groups around the
aquarium throughout the test period with noindicationof the
feeding
behavior exhibited at higher light levels.
The shad ate an average of 1.4 brine shrimp per test at 0 fL of
light.
These data indicate that the minimum light threshold for parti­
culate feeding was between 9 x 10""^ and 9 x 10~^ fL.
Counting errors (average -1.3) were estimated by counting the
brine shrimp in five control experiments where no fish were present.
A Kruskal-Wallis One-Way Analysis of Variance (Mosteller and Rourke,
1973) indicated that the results at 9
x 10~^ fL, 0 fL, and the controls
were not significantly different at the 0.10 level.
Table 5,
The average number of adult brine shrimp eaten in five
experiments (with five fish per experiment) at each of
six light intensities. .
Light Intensity
in Foot-Lamberts
Average
Number Eaten
Standard
Error
9 x 101
259.0
16.1
9 x 10-1
271.0
7.6
9 x 10-3
109.0
16.1
104.0
16.5
2.4
1.3
0
1.4
0.8
Controls3
—1 .3
0.8
9 x 10
-4
9 x 10-5
aNo fish present during experiments.
DISCUSSION
Few phytoplankton feeding fish have evolved in North America
due to the instability of freshwater habitats.over■geological time
(Brooks 5 1968; Larkin, 1956)•
The absence of freshwater phytoplankton
feeders in the past left an ecological gap that apparently was filled
by the ancestors of threadfin shad that invaded from the sea.
The fil­
ter and particulate feeding abilities of threadfin shad were probably
inherited from these marine ancestors who brought the traits with them
when they invaded freshwater, since the feeding habits and morphology
of extant threadfin shad still closely resemble those of marine clupeids .
(Miller, 1960; Nelson and Rothman, 1973; Longhurst, 1971).
Similar
invasions of freshwater habitats by marine planktivores have occurred in
Asia, where some species similar to threadfin shad have completely '
adapted to freshwater life, and others still move between fresh and salt
water (Munro, 1967; Herre, 1953; Nelson and Rothman, 1973).
My observations of filter feeding by threadfin shad are the
first recorded for this species, and confirmed Miller/s (1961) conclusion
that threadfin shad filter feed on relatively small food particles and
consume large prey individually.
The effect of food size on feeding
behavior by threadfin shad is similar to that found in other species
capable of both filter and particulate feeding (Leong and 0 fConnell,
1969; Loukashkin, 1970).
.17
18
The ability of threadfin shad to filter microscopic phytoplank-*
ton or capture larger zooplankton individually may account for the close
correlation between the.types of organisms in the plankton and their
occurrence in shad stomachs found by Miller .(1961).
In addition, by
feeding on different types of plankton in proportion to their abundance,
threadfin shad should be able to change their diet according, to the
seasonal succession of the plankton. For example, May (1968) found
copepods and cladocerans were eaten as the major foods in the spring
and summer, probably when these organisms were relatively abundant, but
phytoplankton became more important during the rest of the year, when
these organisms were probably most common,
Haskell (1959) found similar
seasonal changes in the diet of threadfin shad, however, neither of
these two studies detailed the composition of the plankton where the
shad were collected»
In my experiments, threadfin shad filter fed under both light
and dark conditions, which raised the question as to whether they used
different senses to detect food in the light than in the dark.
However,
no studies have yet been made to determine which senses are used by fil­
ter feeders to detect food*
Volkova (1973) found that the Baikal omul
(Coregonus autumnalis migratorius) filter fed only when it was too dark
to see its zooplankton prey, and presumed that this species sensed the
prey brought into its mouth by respiratory currents with the taste buds
located there»
I made no special studies to determine the senses initi­
ating filter feeding in threadfin shad, but some of my observations
during the filter and selective feeding experiments indicated that
19
filter feeding in this species is probably triggered by chemoreception
and not by vision.
There are two reasons why vision as a triggering
mechanism seems improbable: (1) the shad did not start feeding until
several minutes after brine shrimp nauplii or phytoplankton were added
at high light levels 9 even through the addition of these organisms
caused obvious visual changes by coloring the water; and (2) in experi­
ments where large brine shrimp were introduced, the shad fed immediate­
ly •
Two other observations support a chemosensory trigger; (1) thread-
fin shad have receptors resembling taste buds at the entrance to their
pharyngeal organs (Schmitz and Baker, 1963), which these authors
suggested are used to detect microscopic foods; and (2) threadfin shad
have been observed by T. McMahon, graduate research assistant (personal,
communication) to be attracted to and sometimes make filter feeding
movements near a source of water devoid of any suspended matter, but
previously inhabited by zooplankton.
The experiments using adult brine shrimp clearly showed thread­
fin shad use vision for particulate feeding, because, (1) of the rapid
consumption of brine shrimp at high.light intensities; and (2) the
feeding rate decreased with decreased light intensity (Blaxter, 1970).
Most planktivores are visual feeders and are limited to feeding
in daylight and twilight (Woodhead, 1966; Volkova, 1973).
A comparison
of the filter and particulate feeding abilities of the threadfin shad
at different light intensities to natural light intensities at various
times of the day is shown in Figure 1.
These data indicate threadfin
shad can filter feed 24 hr a day, and that filter feeding is mainly
limited by concentrations of microscopic food.
Farticulate feeding by .
70
60
60
50
50
40
40
30
30
20
20
PERCENTAGE
0 -
PARTI CULATE
70
BY
80
EATEN
80
FOOD
90
OF
90
PERCENTAGE
100
OF
FISH
FILTER
FEEDING
100
FEEDERS
20
! L O G LIGHT I N T E N S I T Y IN F L
1
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( S T A R L I G H T ^ rF U L L M O O N *
^S UN S ET*
i
DAY L I G H T
Figure 1.
Comparison of the filter feeding (solid line) and particulate
feeding (broken line) abilities of threadfin shad to light
intensities in the field.
21
shad, which is limited by light intensity, seems to be possible in light
intensities as low as bright moonlight.
These feeding patterns,are
supported by observations of Baker and Schmitz (1971), who inferred
from stomach analyses that the shad ate larger amounts of zooplankton
during the day than at night, but ate large amounts of phytoplankton '
both day and night.
In conclusion, my study confirms that threadfin shad use.
both particulate and filter feeding, that the type of feeding used is
closely correlated to the size or concentration of food, and that light
intensity only affects particulate feeding.
This knowledge makes it
possible to understand why previous workers have found all the major
groups of plankton in the stomachs of threadfin shad that they examined
(Miller, 1961; Gerdes and McConnell, 1963; Haskell, 1959; May, 1968;
Baker and Schmitz, 1971).
LITERATURE CITED
Baker,
]. D„ and E. H« Schmitz. 1971« Food habits of adult gizzard,
and threadfin shad in two Ozark reservoirs. Pages 3-11. In
G. E. Hall (ed.) Reservoir Fisheries and Limnology. Amer.
Fish. Soc. Spec. Publ. 8 . Washington, D. C.
Blaxter
J. H. S. 1966. The effect of light intensity on the feeding
ecology of herring. Pages 393-409. In R. Bainbridge, G. C.
Evans, and 0. Rackham (eds.) Light as an Ecological Factor.
Symp. Br. EcOl. Soc. 6 . John Wiley & Sons, Inc. New York.
Blaxter
J. H. S. 1970. Light. Animals. Fishes. Pages 213-320. In
0. Kinne (ed.) Marine Ecology Vol. I, Parti. Wiley-Interscience, London.
Brooks, J. L. 1968. The effects of prey size selection by lake planktivores. Syst. Zool. 17:273-291.
Direnner
R. W. and W. J. O'Brien. 1976. The feeding rate and electivity of gizzard shad. SFA 21(2):72.
Durbin, A. G.
and E. G. Durbin. 1975. Grazing rates of the Atlantic
menhadeh (Brevoortia tyrannus) as a function of particle size
arid concentration. Mar. Biol. (Berlin) 33:265-277.
Gerdes, J. H. and W, J. McConnell.
1963. Food habits and spawning of
the threadfin shad in a small, desert impoundment. J. Ariz.
Acad. Sci. 2:113-116.
Haskell
W. L. 1959. Diet of the Mississippi threadfin shad, Dorosoma
petenense atchafalayae, in Arizona. Copeia 1959:298-302.
Heire ,. ,1. W, <-1958.
Marine fishes in Phillipine rivers and lakes.
Phillip. J. Sci. 87:65-88.
Hunter, J. R.
1968. Effects of light on schooling and feeding of jack
mackerel, Trachurus symmetricus. J. Fish. Res. Bd. Can. 25:
393-407.
Janssen, J.
1976. Feeding modes and prey size selection in the alewife
(Alosa pseudoharengus). J. Fish. Res. Bd. Can. 33(9):1972-1975.
Larkin, P. A.
1956. Intraspecific competition and population control
in freshwater fish. J. Fish. Res. Bd. Can. 13:327-342.
22
23
Leong, Ro J» H. arid. C , P « 0 TConnell, 1969. A laboratory study of
particulate and filter feeding of the northern anchovy
(Engraulis mordax), ■ J. Fish. Res. Bd. Can. 26:557-582.
Longhurst , A. R. 1971. . The,clupeoid resources of tropical seas.,,
Pages 349-385. In H. Barnes (ed.) Oceanography and Marine
Biology: an Annual Review9'Vol. 9.
Loukashkin9 A. S. 1970, On the diet and feeding behavior of the
northern anchovy,:Engraulis,mordax (Girard). Proc. Calif, Acad.
Sci. Ser. 4, 37:419-458.
May5 B.
1968. The threadfin shad in North Carolina waters. Job X-B
Biology of the threadfin shad„ North Carolina Division of
Inland Fisheries F-16-R. 13 pp.
Miller, R. R, 1960. Systematics and biology of the gizzard shad
(Dorosoma cepedianum) and related fishes, U.S.F.W.S. Fishery
Bulletin 60(1973):371-388,
•
M i l l e r R , R, 1963. Genus Dorosoma Rafinesque 1820. Gizzard shads,
Threadfin shads. Pages 443-451. In Y . E. Olsen (ed.) Fishes
of the western North At Ian tic ,..Part 3» Bears,: Found, Mar, Res,
New Haven, Conn.
Miller, R, V, 1961. The food habits and some aspects of the biology
of the threadf in shad, Dorosoma petenense (Gunther) . M. S:. .
Thesis, Univ. of Arkansas, Little Rock, 46 pp.
Mosteller,, F. and R. E. Rourke, 19.73, Sturdy Statistics.
Wesley Pub. Co., Reading, Mass, 395 pp.
1Addison-
Munro, I. S, R. 1967. The Fishes of New Guinea^ Dept, Ag., Stock and
Fisheries, Port Moresby, New Guinea, 651 pp.
Nelson, G, and M. N. Rothman. 1973, The species of gizzard shads
(Dorosomatinae)x with particular reference to the Indo^Pacific
Region. Bull. Am.. Mus, Nat. Hist. 150:131^206.
Schmitz, E. H. and C» D. Baker, 1969. Digestive Anatomy of the Gizzard
Shad, Dorosoma cepedianum and the Threadfin Shad, 1). petenense,
Trans, Am. Microsc. Soc. 88(4):525—546,
Thompson, R. H. 1959, Algae, Pages 115-170. In W, T. Edmondson (ed;)
Freshwater Biology. John Wiley and Sons, Inc, New York,
Volkova, L. A. 1973. The effect of light intensity on the availability
of food organisms to some fishes of Lake Baika. J. Ichthyol.
13:591-602. •
24
Withrow, R. and A. Withrow. 1956. Generation, control, and measure­
ment of visible and near-visible radiant energy. Pages 125-258.
In A. Hollaender (ed.) Radiation Biology. McGraw Hill, New
York, N. Y.
Woodhead, P. M. J. 1966. The behavior of fish in relation to light in
the sea. Oceanogr. Mar. Biol. Ann. Rev. 4:337-403.