CHAPTER V

ENERGETICS OF FEEDING AND REPRODUCTION FOR MALES AND FEMALES

OF THREE SPECIES OF HAWAIIAN SUTTERFLYFISHES

INTRODUCTION

An animal's fitness depends on acquiring energy by feeding, and

partitioning this energy between reproduction and other metabolic

demands Calow 1985!. Many foraging models use energy intake from

feeding as the major currency in the determination of fitness Pyke et

al. 1976!, These analyses assume a relationship between energy intake

and reproductive fitness. Each animal, however, must partition usable

energy among the demands of current reproduction, maintenance

activities, growth, and storage for future survival and reproduction.

In addition, there is an unavoidable loss of energy in the form of

heat and unutilized waste products. Zf energy is a limited resource,

then energy budgets of animals will be sensitive to natural selection

Anderson 1967; Calow 1984!.

Animals can meet their energy budgets by adjusting their energy

intake by changes in foraging behavior, or by adjusting how this

energy is partitioned. An individual animal's activity levels,

foraging behavior, and partitioning of energy may all differ between

the reproductive and non-reproductive seasons Elliot 1979; Soofiani

275

and Hawkins 1985; Wootton 1985! . The energetic trade-o ff between

current reproduction and growth and survival for future reproduction

is a basic premise of life history theory Wi1.1iams 1966; Stearns

1976!.

Energy budgets may also differ between the sexes. Females are

expected to contribute more energy into each reproductive effort than

a male Bateman 1908; Trivers 1972!, a situation resulting from

anisogamy, where the female's energy investment in ova is greater tl

the male's investment in sperm. Although males may contribute

significant amounts of energy to offspring in terms of parental care,

it is the initial inequality of anisogamy which is considered to be

the basis of many social systems Trivers 1972; Wilson 1975; Emlen and

Oring 1977!. In situations without parental care, such as occurs in

broadcast spawning reef fishes, the inequality of male vs. female

investment in offspring is expected to be a predominant factor

affecting mating systems.

Schoener �969, 1971, 1983! broadly categorized animal foraging

strategies as lying along a continuum from foragi~g "time minimizers"

to "energy maximizers". Time minimizers limit their feeding time to

the minimum necessary to meet their daily metabolic requirements.

This maximizes the time available for other activities. Ebersole

�980! has termed this an energy maintenance strategy. In contrast,

energy maximizers forage to maximize their daily rade of energy

intake. Energy in excess of that needed for metabolic maintenance may

be channeled into increased reproduction or stored for future use.

276

Schoener �971! proposed that in many species, males tend to be

foraging time minimizers, while females tend to be energy maximizers.

Finally, different species wi.th different energy budgets are

expected to have differing patterns of energy intake and partitioning,

These differences may be reflected in different social systems.

Studies of energy budgets in fishes have concentrated on

freshwater species, predominantly salmonids, under hatchery or

laboratory conditions Elliot 1976, 1979; Brett and Groves 1979;

Brafield 1985!. Field studies of several temperate freshwater fishes

reveal seasonal differences in energy intake and partitioning

reviewed by Soofiani and Hawkins 1985!. Evidence for sexual

differences in energy budgets is less common Newsome et al. 1975;

Diana 1983; Wootton 1985!. Very few studies of reef fishes have

measured energy intake and partitioning from an ecological perspective

Muir and Niimi 1972; Brett and Groves 1979!. For several reef fish

species, where sexual differences in foraging behavior are known,

females feed more than males: e.g. acanthurids Robertson et al.

1979!, pomacentrids Kbersole 1980!, labrids Ross 1983, Green et al.

1984! and scarids Warner and Downs 1977!. Hoffman �983! found that

in protogynous gi~da~s spp. females reduced their foraging time when

they changed sex to become males.

It is generally assumed that additional energy intake by female

fish is channeled into increased egg production. This assumption has

rarely been tested Wootton 1985!. Hirshfield �980! showed that

increased food rations led to higher female fecundity in the Japanese

277

fecundity per spawn was limited by female size, however, food ration

was the most important factor determining the number of spawnings per

breeding season Wootton 1977, 1985!.

The present study compares energy intake and energy partitioning

hy mains and fsmalss of tmo coral-fasdfng huttarflyfishss, ~chs codon

"* I

6b

coral and supplements its diet with algae and polychaetes Hobson

1974; Hourigan Chapter III! . These species have similar social

systems, consisting of long term, apparently monogamous pairs in which

both sexes defend a shared feeding territory Tricas 1985, 1986;

Hourigan 1986a, Chapter III!. The findings from these two species are

compared to data collected during the breeding season of a third

butterflyfish, ~ergo i~ ~~, which exhibits a haremic social

system Hourigan 1986b, Chapter IV!, It is an omnivore which feeds

primarily on polychaetes and algae Hobson 1974, Hourigan Chapter IV!,

All three species are broadcast spawners, which release gametes into

the water column and show no parental care. A series of eight

experiments were conducted to determine seasonal and sexual

differences in energy intake and absorption efficiencies, and the

partitioning of this energy between somatic, storage, and reproductive

tissues. These results are compared to field observations of feeding

and activity in these species.

278

METHODS AND RESULTS

Z. Study sites and field collections:

Methods:

C

coral reefs at Puako, Hawaii Lat 19 58'N, Lon 155 51'W; for a

complete description of the habitats and observation methods see Hayes

et al. 1982; and Hourigan Chapter lI and ill!. The third species,

~Cltaetod freebll, eas rare at Puako. Therefore, observatfons and

collections were conducted in similar habitats at Kahe Pt. Lat 21

21'N, Lon 158 8'W! off the leeward coast of the island of Oahu

made at Kahe Pt. and at coral poor areas at Portlock, Oahu Lat 2lo

16'N, Lon 157 4'W!,

collected by spearing at Puako during three times of the year: the

non-breeding season in fa11 November 1980!, the height of the

breeding season in spring March 1981!, and the end of the breeding

season in summer July, 1981!. individual C ~f em~ were collected

at Kahe Pt, Oahu during the spring March 1981!. Additional

November 1983. Each fish was either dissected immediately, or

labeled, double bagged and frozen for later analysis.

279

In the laboratory individual fishes were thawed, and standard

length SL! and wet weight were measured. Fishes were then dissected,

and the liver, gonads, and fat deposits surrounding the intestine

removed and weighed. Three small sub-samples from each ovary were

removed, weighed, fixed in l0% formalin and preserved in 70% alcohol.

Numbers of vitellogenic eggs vere counted and staged according to the

methods of Hourigan and Kelley �985!. The remaining tissues as well

as food material from the pouchlike stomach, and portions of feces

from the rectal region were saved to be utilized in the experiments

described below.

Results.'

female ~ ~emb~ was collected. Pairs were composed of one male and

one female, both reproductively mature. Length-weight relationships

for males and females of the same species were similar, indicating

C

size. In both paired species, males vere usually larger than their

pair-mates paired t-tests, p�.05 for both species!. The mean size

"c

a The haphazard collection of C

~fremb precluded similar comparisons. Observations of harems

280

Figure 5.1a Length-weight relationship for males and females of three. b! ~

uadrimaculatus, and c! C f~em~b

20

0 sL mm!

282

Figure 5. lb Length-weight relationship for males and f'emales of three

283

~ ~ ~ ~ ~ I ~80

60

20 sL mm!284

Figure 5, lc Length-weight relationship for males and females of threespecies of Hawaiian butterflyfishes: c! ~ ~i~~.

285

20 sL mm!286

indicated that males were visibly larger than their associated

females.

Gonosomatic indices CSI 100 X ratio of wet weight of gonad to

total wet weight of body! of both males and females of the paired

species were highest during the spring Table 5.1!. Comparisons of

GSIs of fish with very different body sixes are difficult due to

associated body-gonad allometries deVlaming et al. 1982!, There

were, however, no significant differences within each species among

the body sizes of fish in the three seasonal samples Independent one-

way ANOVAs, p�,5!, Fecundity, defined as the the total number of

vitellogenic oocytes yolked eggs! contained in the ovary of a female,

was also highest in spring, as was the median ova diameter Table

5.1!. Almost all vitellogenic oocytes were of a similar size and

stage of development. Hydrated eggs were only found on two occasions,

c- ~

prior to the new moon. Spawning was also observed on that occasion.

Examination of the two ovaries containing hydrated eggs showed that

77% to 82% of large vitellogenic eggs had undergone hydration

synchronously. This allo~ed estimation of the batch fecundity,

defined as numbers of eggs spawned at one time, estimated as 79.54 of

the total number of vitellogenic eggs Table S.l!, assuming that the

two remaining species spawned a similar proportion of all vitellogenic

oocytas. ~Chaeeoda ~ambit had the largest estimated batch fecundity

Preliminary histological observations of the testes of all three

species revealed no evidence of protogynous sex change. Testes

287

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contained no atretic oocytes, nor- was a membrane lined ovarian lumen

remnant present.

In addition to the adult fishes, six non-territorial 9

collected in March 1981. These fish were significantly smaller than

territorial individuals of the same species independent t- tests for

males and females, p�,01!, Both males and females were represented,

but neither were sexually mature i.e. ovaries did not contain

vitellogenic oocytes, and testes did not contain live sperm!.

IZ. Field and Laboratory Kxperiments.

The following experiments were designed to estimate rates of

energy intake in the field, in order to determine how this energy was

partitioned, and to estimate spawning rates of females.

Experiment 81.: Energy intake per feeding bite.

Methods:

in the field by divers using hand nets. These fishes were transported

to the Hawaii Institute of Marine Biology in aerated buckets and

placed in large �00 1! tanks with flow-through filtered seawater and

plastic tubes for shelter. Live coral colonies coral heads! were

placed in each tank for food, and the fish were left undisturbed for

289

at lease 24 hrs. All coral colonies used in these experiments were

collected from Kahe Pt. and different locations in Kaneohe Bay,

Individual, healthy colonies were removed and transported back to the

laboratory where they were kept in an outdoor water table wi.th free

flowing sea water. Fresh corals were collected on the day before each

experiment,

Prior to the experiment, an individual was transferred to a 40 1

aquarium along with a freshly collected coral colony of a particular

species, Only fish which fed on the offered coral colony were used.

After 30 min the coral colony was removed, and the fish starved for 24

hrs to allow gut clearance and acclimatization to the test aquarium.

On the following day, a new coral colony of the same species

previously offered, was placed in the test aquarium, separated from

the fish by a clear partition. After one hour, the coral polyps had

expanded. and the partition was removed. Each experimental fish was

observed for 30 min following its first bite on the coral. All

feeding bites were counted by an observer sitting quietly 2 m from the

aquarium, or recorded on videotape for subsequent counting. The

behavior of fishes did not appear to differ during early trials of

these two recording methods, so all subsequent observations were

conducted with an observer present. Eight replicate trials with C

were conducted, with each of the three most abundant

Hawaiian coral species ~Peri ~abate, giHHi~e ~coa ~es and

290

After' 30 min, the experimental fish was removed from the

aquarium, sacrificed immediately, weighed and measured SL! . The fish

was dissected, its sex determined, and stomach contents were removed.

The length of the gut was measured, and the distance cleared by food

from the px'evious day was measured. The stomach contents vere

inspected, weighed, then dried to constant weight in a 60 C oven.

Each sample of dried stomach contents vas ground and homogenized

using a mortar and pestle. The homogenate was further subdivided into

sub-samples which were formed into pellets, weighed, and either ashed

at 500 C and re-weighed to determine ash free dry weights AFDW!, or

combusted in a Phillipson oxygen microbomb calorimeter, as describedR

by Paine �971!, to determine caloric content. In general, four sub-

samples of each dried tissue were analyzed for AFDW, and four to five

sub-samples � to 20 mg each! were analyzed for caloric content. In

this manner, dry weights, ash-free dry weights and caloric values were

obtained for the samples. These were then calculated on a per-bite

basis.

Results.

o

introduced to the aquarium. The amounts of each coral ingested are

summarized in Table 5.2. More than 95% of the material ingested in 30

min remained in the pouchlike stomach. Organic content and caloric

content cal/mg AFDW; 1 cal - 4.81 joules! wex'e slightly higher for

stomach contents of fish feeding on ~ ~scend ina than for those of

291

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fish feeding on the two pi~~ spp. Net intake in calories per bite

was higher for fish feeding on g ~me ~na than those feeding on

2 ' I'

feed.

Examination of the stomach contents of fishes feeding on P

medea ~ showed complete oral disks with tentacular rings. Only a

few such rings were visible in the stomachs of fish feeding on ~~eg

spp.. No calcareous material was ingested. Examination of the corals

themselves revealed that most polyps on g<~~s spp. were still intact

with perhaps only portions of one polyp removed per bite, After a

single bite, polyps in a 10-15 mm radius of the bite retracted

completely into the calyces within 15 seconds. Additional polyps were

partially retracted in a radius of 20-30 mm around the bite. If left

undisturbed, polyps would come out after 3 to 6 min.

Experiment 82. Energy intake per feeding bite: Field observations.

Methods:

To determine energy intake per feeding bite in the field, two

subsequently followed for 30 min after they had begun feeding. The

number of feeding bites by each fish on different substrata were

counted. The fishes were then speared, placed in plastic bags and

293

returned to the laboratory on ice. Fishes were weighed and measured,

and their stomach contents removed, dried and processed as in

Experiment ¹1. These energetic values could then be compared ta

values from Experiment ¹1 and field observations of feeding.

Results:

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the hard substratum. There was some feeding on g ~i~L. The third

species, ~ ~<~3~ fed on the hard substratum, in crevices, in the

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in the stomach. Inspection of stomach contents revealed that C

contents included large numbers of zooxanthellae and both intact and

discharged nematocysts, Stomach contents of C. u drimaculatus

contained coral material as well as polychaetes, small crustaceans and

algae. The stoaach contents of t ~frembli' contained only

polychaetes, crustaceans, algae and sea urchin pedicillaria. Females

of all three species had more material in their stomachs, and a

greater calculated energy intake than did males Table 5.3!.

294

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Experiment 4 3. Rate of food clearance through the gut,

Methods:

Energy absorption from food intake depends in part on the time

that food remains in the gut. A rough measure of the rate of food

clearance through the gut was determined by sacrificing fish at 6, 12,

24 and 48 hrs after they were fed, and measuring the amount of the

stomach and intestine which was cleared of food material. Two male

The guts were removed, the length of the intestine was measured, and

the portion which was cleared of food was recorded.

Results:

After 6 hrs, the stomach was empty, as well as the first 32% SD

4.6%! of the intestine. After 12 hours, 82% SD 8.5%! of the

intestine had been cleared of food, After 24 hrs 88% SD 2. 3%! of the

intestine was cleared. Same fecal material was still retained in this

last 12% even after 48 hrs. There were no consistent differences

between males and females. Sample sizes in this experiment were small

from experiment 1 and all three species from

experiment 2 had similar percentages of cleared areas corresponding to

the last time they had fed.

296

Experiment «4. Estimation of caloric intake and absorpt.ion.

Methods:

In this experiment, the caloric intake and relative absorption

assimilation! efficiency of male and female fishes were determined.

Food in the stomachs of teleosts is sub! ected to the action of HC1 and

peptidases, but little or no absorption occurs there Kapoor et al.

1975!, Thus as feeding is relatively continuous Hourigan Chapter

III! and food mo~es at a constant rate through the gut Experiment

«3!, the energy content of the diets of fishes can be estimated by

analyzing the energy content of the stomach contents Talbot 1985!.

In butterflyfishes, the stomach is followed by a very long intestine

where most absorption of nutrients occurs. At the distal end of this

intestine is a short rectal region. The energy content. of material in

this region probably approximates that voided in the feces.

t

were collected by spearing in November 1980, March 1981 and in July

1981, at Puako, for a total sample of 48 fish of each species. Pair-

mates were collected at. the same time, but different pairs were

collected at different times of the day. Six individual male and six

female C Stern'blti vere collected in the afternoon on several

different days in March 1981 at Kahe Pt.. Fishes were frozen

immediately, and subsequently partially thawed before analysis. This

allowed removal of the stomach contents and feces with little

contamination by material from the remaining portion of the intestine

Talbot, 1985!. Samples of stomach contents and feces from each fish

297

vere dried and analyzed as in Experiment ¹1. In this manner the

organic content and caloric content of the food and feces vas

estimated.

Results:

in their stomachs than did the males with whom they were paired. The

the weight of stomach contents of their mates, speared at the same

time N - 24; Paired t-test p<0.001!. Stomach contents of male C

4

their mates N 24, Paired t-test p�.001!. This vas true even

though males vere on average larger than thei,r mates. Because male

and female 9 fZyg~ were not collected at the same- time, similar

comparisons of stomach content weights could not be made.

Stomach contents were of similar composition to those in

Experiment ¹2. For the paired species there were no significant

differences between pair members in the percent organic content of the

stomach contents organic density: 100 X AFDW/dry weight! ot' in the

energetic content per gram -caloric density expressed as cal/mg AFDW;

paired t test p ! 0.5; Table 5.4!. This is in accordance vith

observations that both males and females fed on similar foods. There

were no differences between male and female g ~~ in the organic

or caloric densities of stomach material t-test p > 0.25! .

298

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All three species had very long intestines. The ratio of body

length SL! to intestine length measured fram the pyloric sphincter

and 1:6.67 SD 1.31! for C frem~,

Within each species, there were no differences in these ratios between

the sexes Independent t-tests, p ! 0.8!, nor did there appear to be

differences in the shapes of male and female guts, The fecal

material at t! end of the gut had very little recognizable material

except. for la; e numbers of apparently undigested sooxanthellae in the

guts of the two coral-feeding species. Again, for each species there

vere no significant differences between males and females in the

percent organic content of the feces.

A coefficient of absorption efficiency assimilation efficiency!

of organic material, Aa was calculated using the equation adapted

from Fange and Groves l979!:

0 organic content of fecesA - 100 X 1o 0 organic content of stomach contents

A similar equation gives the calaric absorption efficiency, A

Calories per rag dry wt. of fecesA 100 X 1

c Calories per mg dry wt. of stomach contents

There was no difference between males and females within the same

species in either measure of efficiency Table 5.4!. For the two

paired species there were no significant differences in energy density

of the food intake or in absorption efficiencies between seasons.

300

There was, however, a great difference in the absorption ef ficiencies

of ~ ~i~ compared to the the remaining two species One way

ANOVA, p<0,01!, ~hae i~do ~m~b appeared to absorb two to three

times as much organic material from its diet than did the other

species, resulting in a higher net energy intake.

Experiment ¹5, Estimation of caloric partitioning among different

tissues by males and females of the three species.

Methods:

In this experiment, the energetic content of the body tissues of

the fishes of all three species used in Experiment ¹4 N - 48 C

f "MJU

After the guts were removed, the remaining tissues were divided into

gonads, liver, gut mesenteries with attached fat deposits, and the

remaining carcass. A tissue sample from the dorsal musculature was

also removed. The remaining carcass was dried, weighed, then ashed

for a determination of the ash-free dry weight. Each of the other

tissues was dried, weighed, homogenized and formed into pellets as

described above.

Ash-free dry weights and caloric contents were determined from 5

sub-samples of each tissue as described in Experiment ¹1, Because of

the small size of testes, fewer sub-samples �-5! were used. Since

the fat deposits yielded liquids when dried, the ash-free portions

301

were assumed to be lipid, and were given a value of 9,45 cal/mg AFDW

for comparative purposes. This value is the energy physiologically

available in lipids Brett and Groves 1979!.

Results:

Tissues were divided into three ma]or categories: reproductive

tissues the ovaries and testes!, storage tissues the fat stores of

the intestinal membranes and the liver!, and other somatic tissues

represented by the sample of muscle tissue and the rest of the body!.

The distribution of oz'genic content and energy among these different

tissues is shown in Table 5.5 and 5,6, Organic density is represented

as a percentage ratio of ash-free dry weight AFDW! to total dry

weight of the tissue, and represents the percent of organic material

in the tissue. Caloric density is presented as cal/mg AFDV and

zepresents the energy content of organic material in the tissue. In

addition, the percentage of the total organic content of the animal

which is comprised by that tissue Fig. 5.2! provides a rough

approximation of the percent of net organic intake devoted to that

tissue. In the case of reproductive tissues, this provides a first

approximation of reproductive effort RE! for comparative purposes.

Reproductive tissues showed the greatest difference between the

sexes in tissue energy content. The ovaries of females contained 8 to

15 times as many calories as did the testes of males, even though male

302

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Ff gure 5, 2, Partitioning of organic material in different tissues of'C-~'" C-~ u tus, during the

fall, spring, and summer. Values represent the mean percent + 95%confidence limits! of. the total organic content of the body which iscomprised by the organic content of a particular tissue. The organiccontent of the tissues was determined from their ash-free dry weights.The tissues are: a! the gonads, b! the viceral fat. For each season,the sample for each species consisted of eight fish of each sex.

307

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M %see awaaerSeason

Qyyhy QuasarSeason

8P4ay SeamerSeason

f4 %!thy herseSeason

Figure 5.2 cont.! Partitioning of organic material in different

during the fall, spring, and summer. Values represent the meanpercent + 95% confidence limits! of the total organic content of thebody which is comprised by the organic content of a particular tissue.The organic content of the tissues was determined from their ash- freedry weights. The tissues are: c! the liver,: and d! the remaining bodytissues. For each season, the sample for each species consisted ofeight fish of each sex.

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%ghee SeeeerSeason

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