Bulletin of the Japanese Society of Scientific Fisheries Vol. 34, No. 1, 1968 29

An Experiment to Estimate the Satiation Rate of Feeding in Fish*

Teiji KARIYA**, Soichiro SHIRAHATA***, and Yasue NAKAMURA** (Received September 26, 1967)

The information on satiation feeding will provide a basis for further studies of feeding habits of fish in nature and also for evaluation of feeding management related to the maximum growth in fish culture. An actual feeding method has also far been used to obtain the satiation rate of feeding. In this method, however, it is difficult to raise a feeding rate up to satiety, because of the difficulties in keeping the feeding activities and abiotic enviromental conditions best. Accordingly in order to estimate the amount of food required up to com plete satiety, we attempted to develop another type of method instead of the feeding one. In feeding experiment with young mackerel, it was observed that the stomachs of the well-fed fish distended to such a extent that they sometimes bursted by rough handling1). This phenomenon suggests that the volume of stomachs expanded till they burst may be equal to that of stomachs of the fish which devour food to satiety. Consequently some technique has been desired by which the stomachs are made to expand to burst. We applied several methods in the early stages of the study, but without success; for instance liquids or solids such as small shots were tried to introduce directly into stomachs, but failed to expand them. Recently, however, a new method has been well developed in our laboratory. This method is characterized by the application of air inflation, by which the stomach can be expanded easily to its fullest extent. The experimental procedure and some information obtained with rainbow trout and other 52 species of fishes are presented in this article. There is no report concerned with stomach volume in fish except in a crustacean, the Japanese spiny l obster.****

Material and Method

Stomachs were used under the conditions where they were taken out of the bodies

* The outline of this work was reported at the General meeting of the Japanese Society of Scientific Fisheries, Tokyo, April, 1965. ** Department Fisheries , Faculty of Agriculture, Tohoku University, Sendai(狩 谷 貞 二 ・ 中 村 恵 江,東 北 大 学 農 学 部 水 産 学 科). *** Nikko Branch Station , Freshwater Fisheries Research Laboratory, Ministry of Agriculture and Forestry, Nikko(白 旗 総一 郎,淡 水 区 水 産 研 究 所 日 光 支 所). **** KUBO2) and INOUE3) measured the stomach volume of lobster by introducing emery powder and water respectively into the stomach, which consists of chitinous substances. 30

or not. In either case it was necessary to push the food out of the stomach using

fingers before measurement. Next a small , thin rubber sac attached to an end of a glass tube was inserted into the stomach, which was then placed in a glass vessel as shown in Fig. 1. This vessel was filled with a 0.8% sodium chloride solution so that the water level in the burette might settle above the lowest graduation mark and was rubber-stoppered tightly so as not to leave air bubbles under the stopper. It was suitable to use a glass tube of 5mm in outside diameter, its one end being sharpened to 1-3mm to which a rubber sac was attached. The size of the rubber sac was 1-2cm in length and 0.1-0.8cc in volume (blank value). Air inflation was conducted by using the rubber bellows or an air pump for the bicycles. The gain in water volume resulted by stomach expansion was measured by burette readings, and at the same time the air pressure in the stomach was measured by Fig. 1. An arrangement used manometer. This procedure was repeated until the to measure critical volume of stomach expanded by stomach bursted. The final reading in volume plus air inflation blank value was regarded as a critical volume of the B: Burette graduated in stomach, and the ratio of this volume and the body 0.1cc units, V: wide mouthed glass vessel, and weight was obtained. Further, multiplying the critical M: manometer. ratio of the stomach volume by specific gravity of food gives the satiation rate of feeding. As for the specific gravity of food some data can be used as follows: 1.05 for raw fish meat or tubifex and 1.2-1.3 for bound diets moisture contents of which are about 50%.

Results and Discussion

Effects of feeding on the expansion of the stomach. Fig. 2 shows the course of the expansion of the stomach as air pressure become higher. Six 3-days starved and six fed rainbow trout of 19-73g in body weight were used. The latter group was fed at a level of about 10% of body weight, Since it was difficult for the starved stomachs to expand owing to the intense contraction of their muscles, time more than 20 minutes and pressure more than 1.6 atp. were often required to burst . Also, since the starved stomach tended to burst in a half way to the fullest extent in expansion, the ratio of the stomach volume amounted to only 10-14% of the body weight. On the contrary, a stomach which had been filled with food was apt to expand with increase in air pressure and its critical ratio of 15-25% was much higher than that of starved stomachs. Post-mortem changes in the stomach expansion. Fig . 3 shows the change in the 31

Fig. 2. Showing the effect of feeding before Fig. 3. Showing the change in measurement on the expansion of stomach volume of rainbow stomach of rainbow trout. Solid line trout after death. denotes fed fish and broken line unfed fish. The numbers in the figure denote the body weight of fish in g. critical ratio of stomach volume with passage of time after death in starved rainbov trout of 28-83g. In this figure, evidently the critical ratio showed no remarkabl changes in a day after death, whereas it decreased to a half of the initial value o the third day. Changes in the stomach volume with growth. The critical stomach volumes o fed rainbow trout of 2-270g were measured, and the results were arranged into groups according to their body weight as shown in Table 1. The ratio of the stomac

Table 1. Stomach volume of rainbow trout, and net weight of stomach, expressed as percentage of body weight.

Number Body Stomach volume in % Net stomach weight in offish weighting Range Mean s.d. RangeI Mean s.d.

9 2.1- 4.1 13.5-26.9 18.66 4.62 1.91-2.98 2.45 0.32 8 8.3-17.5 13.6-23.2 18.64 3.16 1.71-2.56 2.11 0.36 15 21.7-37.9 12.1-22.4 17.94 3.14 1.48-2.84 1.92 0.39 14 50.1-83.0 10.8-24.6 15.57 3.56 1.39-2.12 1.74 0.20 15 128-274 9.2-21.9 13.25 2.97 1.12-1.99 1.63 0.29

s. d.: Standard deviation 32

volume tended to decrease with growth, showing higher values of about 19% for the smaller fish of 2-4g, and lower values of 13% for the larger than 100g. A similar tendency was observed in the change in net weight of the stomach against the body weight. Therefore, the fact that the ratio of the critical stomach volume to the body weight decreases with growth may be associated with the relative growth of the stomach itself. Furthermore, it is conceivable that the feeding capacity of larger fish, that is, the expansion of their stomachs, may be reduced with the course of growth or the fattening of their bodies, because the abdominal wall strengthens and fat deposits in the adipose tissues adjacent to the digestive tracts.

The critical ratio of the stomach shown in Table 1 may compare with the satiation

rate of feeding determined by the rearing method. From the results of feeding

experiments, the highest values of feeding rate were 24.1% in case of cannibalistic

feeding of a rainbow trout of 27.7g and 29.4% as the highest stomach content for a

rainbow trout of 0.35g fed with chironomid larvae. Evidently these values closely

approximate the highest ratios of 27-22•“ shown in Fig. 1.

Effects of chemical relaxatives on the stomach expansion. Among the chemicals

which relax the smooth muscle, papaverine hydrochloride which is known to be a

musculotropic relaxative and atropine sulphate which is known to be a neurotropic

one, were tested to confirm whether they have distinctive effects on the stomach

expansion. The concentrations of the chemical solutions were 50 ppm in the former

and 1 ppm in the latter. Either solution contained 0.8% of sodium chloride. The

stomach expansion was conducted in the bath of either solution.

Table 2. Effect of papaverine and atropine on the expansion of starved stomach of rainbow trout.

Treatment Number Body Stomach volume in of fish weight in g Range Mean s. d.

Papaverine, 50 ppm 7 21.2-35.2 10.8-15.7 12.6 2.30 Atropine, 1 ppm 7 21.6-35.2 10.4-16.8 13.7 2.60 Control (unfed fish) 7 21.5-40.4 10.9-16.1 13.7 2.28 Control (fed fish)* 15 21.7-37.9 12.1-22.4 17.9 3.14

* Data from Table 1 .

The test fishes were rainbow trout of 10.6-13.5cm in body length, starved for

48 hours at 14•Ž. They had empty stomachs at the time of dissecting their abdomen . As shown in Table 2, the stomach volume treated with the chemicals was almost equal to that of unfed fish and was less than that of the untreated stomachs of fed fish. Therefore, these chemicals are not considered to be effective for the purpose of expanding the starved stomach.

Critical volume of stomach in 52 species of fishes. Stomach measurements were 33

carried out with 52 species belonging to 25 families, except rainbow trout. Of these, marine fishes were obtained at the fisheries market in Shiogama City, Miyagi Pref. Besides, the ayu-fish, Plecoglossus altivelis and sardine, Sardinops melanosticta were attempted to test in vain, because rubber sacs for measurements were unable to insert into their stomachs without bursting their alimentary canals owing to their weakness. Several fresh individuals were used for each species. Table 3 shows the highest value in each species. The critical ratio of stomach ranged from 3% of the lowest value to 160% of the highest, the ratios of 37 species being 5-15%. As compared with the results of rainbow trout, the critical ratio seems to be underestimated in some cases. For example in the common mackerel, the highest satiation rate of feeding has been reported to be 23%1) and 23.9%4), and the mean group satiation rate to be 15%1), whereas the ratio of stomach volume observed in this experiment was 13.2%. There fore, the value of satiation rate obtained in this experiment shows the mean group satiation rate. In Table 3, it is also seen that the fishes having larger stomach volume were catfish, mirror perch, angler fish, and elf sculpin, and the last two showed their stomach volume to be 80% and 160% respectively. These fishes are commonly known as the fish having larger stomachs and voraceous feeding habits. As for the fishes having smaller stomachs, blenny and flatfishes are typical ones, most of their stomach ratios being less than 8%. The observation that the flatfishes have a smallest stomach coincides with the results of investigations of stomach content of the species in the sea and those of rearing experiments in which their feeding rate was domonstrated to be at lower levels6). Atheresthes evermanni among the flatfishes, however, showed the largest stomach ratio which amounted up to 20%. This coincides with a report in which Mikawa7) described that this fish is voracious and has a very stretchable stomach. As mentioned above, the critical ratio of stomach volume varies with different species of fish. Clearly this characteristics may reflect the differencies in feeding habits and feeding capacity of stomach of fish.

References

1) T. KARIYA: Suisan-zoshoku (Aquiculture), 4, 1-8 (1956). 2) I. KUBO: This Bull., 27, 1063-1065 (1961). 3) M. INOUE: Suisan-zoshoku (Aquiculture), 11, 143-147 (1963). 4) N. ISHIWATA: ibid., 9, 106-109 (1961). 5) M. HATANAKA,M. KOSAKA,and Y. SATO: Tohoku J. Agr. Res., 7, 151-162 (1956). 6) Y. SATO and Y. ISHITO: Bull. Tohoku Reg. Fish Res. Lab., 20, 106-113 (1962). 7) M. MIKAWA: ibid., 4, 136-146 (1955). Table 3. Critical volume of stomach in fishes of 52 species. 34

Family Species Japanese name Body in length cm Body in weight g Stomachin cc volume Stomachin volume° °

_ ------~_ Osmeridae Hypomesus olidus Wakasagi 10.4 13.1 1.3 9.5 Siluridae Parasilurus asotus Namazu 33.5 294.3 52.5 24.8 Anguilldae Auguilla japonica Unagi 48 144 11.2 7.8 Congridae Astroconger myri.aster Maanago 21.0 153 14.0 17.0 Rhynchocymba mystromi mystromi Ginanago 33.3 64 3.9 6.1 Zeidae Zenopsis nebulosa Kagami-dai 25.7 332 79 54.0 SphyraenidaeSphyraena japonica I Yamatokamasu 25.3 127.6 13.2 10.3 Channidae Channa maculata Taiwan-dojo 22.8 126 15.0 11.9 Scombridae Pneumatophorus japonicas Masaba 15.8 37.8 5.0 13.2 Serranidae Lateolabrax japonicas Suzuki 18.5 90.0 9.0 9.9 Sciaenidae Nibea argentata Ishimochi 14.5 62.2 6.5 10.5 Sillaginidae Sillago sihama Kisu 13.5 28.1 2.1 7.5 Sparidae Evynnis japonica Chidai 10.6 36.0 2.0 5.6 Pomadasyidae Hapalogenys kishinouyei Shimasetodai 12.7 92.2 10.3 11.1 Pholidae Enedrias nebulosus Ginpo 9.1 12.5 0.4 3.2 Stichaeidae Stichaeus nozawai Tauegaji 39.3 312 53 17.0

Scorpaenidae Sebastes owstoni Hatsume 20.8 191 9.7 5.1 S. thompsoni Usumebaru 19.0 182 7.0 3.8 S. taczanonskii Ezomebaru 22.9 287 48.6 17.0 S. inermis Mebaru 17.2 143 10.0 7.0 S. schlegeli Kurosoi 16.6 144 13.7 9.5 S. longispinis Koraiyoroi 19.0 225 37.0 16.4 Sebastiscus marmoratus Kasago 15.0 106 12.0 11.3 Helicolenus hilgendorfi Yumekasago 13.5 66.7 8.0 12.0 Sebastolobus macrochir Kichiji 14.9 64.1 8.1 12.6

Hexagrammidae Pleurogrammus azonus Hokke 32.2 507 75 14.8 Hexagrammos otakii Ainame 19.8 156 19.8 12.7 Platycephalidae Platycephalus indicus Kochi 26.4 168 18.0 10.7 Cottidae Alcichthys alcicornis Nijikajika 22.2 216 29.0 13.4 Hermitripterus villosus Tobetsukajika 18.8 179 284 159 Agonidae Occa iburia Saburo 14.4 26.3 1,6 6.1 Triglidae Chelidonichthys kumu Hobo 22,9 178 23.5 13.2 Lepidotrigla micropterus Kanagashira 14.3 55.5 5.8 10.4

Pleuronectidae Atheresthes evermanni Aburagarei 32.2 306 60 19.6 Hippoglossus stenolepis Ohyo 35.5 455 44.0 9.7 Eopsetta grigorjewi Mushigarei 21.0 176 28.2 16.0 Verasper variegatus Hoshigarei 23.1 231 24.7 10.8 Pleuronichthys cornutus Meitagarei 12.6 52.5 3.0 5.7 Lepidopsetta mochigarei Asabagarei 24.6 279 18.7 6.7 Limanda herzensteini Magarei 15.6 71.1 5.0 7.0 Limanda yokohamae Makogarei 16.9 95.7 5.5 5.7 Dexistes rikuzenius Medamagarei 13.0 39.0 2.4 6.2 Pleuronectes pallasii Tsunogarei 30.9 750 45.0 7.3 Platichthys stellatus Numagarei 22.6 214 15.5 7.2 Kareius bicoloratus Ishigarei 20.5 153 10.0 6.5 Clidoderma asperrimum Samegarei 23.7 290 18.0 6.2 Tanakius kitaharai Yanagimushigarei 18.2 66.6 3.3 5.0 Microstomus achne Babagarei 20.3 142 4.5 3.2 Moridae Lotellamaximowiczi Ezoisoainame( 25.6 188 38.0 20.2 Gadidae Gadus macrocephalus Madara 39.1 645 90 14.0 Theragra chalcogramma Suketodara 35.8 314 31.0 9.9 Lophiidae Lophius lituton Kianko 34.8 732 585 79.9

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