OBSERVATIONS ON THE COMPARATIVE EFFICIENCY OF THE ALLOCHTHONOUS AND AUTOCHTHONOUS FOOD OF FISHES BASED ON THEIR BIOCHEMICAL ANALYSIS CIENTIFIC NOTE

Trabajo recibido el 22 de mayo de 1984 y aceptado para su publicación el 28 de septiembre de 1984.

RESUMEN

INTRODUCCIÓN

Though considerable amount of work has been carried out on the biology and artificial propagation of a number of freshwater fishes, chemical estimations of their flesh in relation to the types of food they feed are limited. This is, however, very important, because, that would help to determine the conversion efficieney of different species, which has a key role to play in the artificial propagation of fighes. Qasim (1972), Qasim and Jacob (1972), Das (1978) and Jacob and Rajagopal (1980) have already stressed the importance of the chemical analysis of the stomach contents of fishes.

The present paper reports the chemical composition of a typical allochthonous and autochthonous food and their comparative efficieney as food as revealed by Rasbora daniconius and Puntius amphibius, their respective consumers.

Nearly 155 specimens of R. daniconius and 150 specimens of P. amphibius collected wild during a three month period between May and July, 1982 were used for the studies. For the chemical analysis whole fish including the ahmentary canal, but without its contents, was used. The gut contents of the two species were separately pooled and put to chemical analysis.

The crude protein was estimated by the miero-kjeldhal method as modified by Horwitz (1970); the nitrogen value was multiplied by the factor 6.25. Fat extractions were done by 1:1 (v/v) chloroform-.-nethanol mixture and 3:1 (v/v) ethanol-ether mixture at 60°C for six hours (Gradwohl, 1963). Carbahydrate (as glycogen) was estimated caloflmetrically, and the ash contents is a muffle furnace at 500-550°C.

Calorie values of both food and fish were obtained by burning 65-135 mg pelleted samples with a 1107 semimiero bomb calorimeter (Parr, Manual number 1421, 1981).

The results are presented in Table 1, which will show that the autochthonous food was richer than the allochthonous food in moisture content. The protein and carbohydrate contents of the allochthonous food were higher than that of the autochthonous food. However, in the fat content the autochthonous food was better than the allochthonous food. The ash content of the autochthonous was three times higher than that of the allochthonous food.

True to the richer contents of protein and carbohydrate, the caloric value of the allochthonous food was 6297.06 cal/g dry weight and that of the autochthonous food, 4178.49 cal/g dry weight, highlighting that the allochthonous food of R. daniconius is more efficient: that the autochthonous food of P. amphibius.

Nevertheless, the calorie value of the flesh of both R. daniconius and P. amphibius was more or less matching, 5694.52 cal/g dry weight in the former and 5560.98 cal/g dry weight in the latter. This is suggestive that the inferior quality of the food of P. amphibius is being compensated by better conversion efficieney.

The levels of the chemical constituents in the food and the flesh of the respective fishes also give some interesting insights into the physiology of the two species. The moisture contents of the flesh of R. daniconius was 72.74 %, whereas that of P. amphibius was 68.20 %, in spite of the lesser moisture content of the food of the former, suggesting that the excretory activity of R. daniconius is not so efficient as that of P. amphibius. Another reason that can be attributed to the higher moisture content: of R. daniconius is the larger quantity of water going down the pharynx into the gut while swallowing the food. R. daniconius has more thickly set gill filaments than that of P. amphibius. This would lead to a lesser amount of water which has been taken into the mouth along with the food, being able to escape through the opercular chamber of R. daniconius than in P. amphibius, resulting in its eventual swallowing.

In both the species the level of protein was greater than that in the food, suggesting that the efficieney for converting protein in both the species is equally good. The lesser fat content of the body than in the food in both the species also highlights a parity of conversion efficieney of fat in both the species. Possibly the lower level of the fat: content in both the species may be due to the synchronisation of spawning activity in both the species, because aceording to Muddanna (1971) and Prem Kumar (1979) the spawning season of both R. daniconius and P. amphibius respectively, coincides with the monsoon season i. e., from May to July.

TABLE 1 DATE OF COLLECTION, LENGTH, WEIGHT AND BIOCHEMICAL CONSTITUENTS OF THE BODY AND INGESTED FOOD OF R. DANICONIUS AND P. AMPHIBIUS.

The more or less equal content of carbohydrate in both the species, even though the autoclithonotis food of P. amphibius was doubly richer in the carbohydrate content than that of R. daniconius, is indivative of the better efficieney of P. amphibius is the utilization of carbohydrate.

Eventhough the ash contest of the food of P. amphibius was nearly three times higher than that of R. daniconius (30. 00 % and 9.33 % respectively) the same in the body of the two species was almost similar. The high ash percentage of the food in P. amphibius was probably due to the high percentage of bottom detritus, sand and mud paricles in the diet which, however, do not from the actual food of the fish. Jacob and Rajagopal (1980), too, found a large percentage of ash content in the food of Sardinella longiceps which ingested the bottom sediments.

One of the authors (K.P.K.) is highly grateful to U.G.C. authorities for awarding a Senior Research Fellowship during the tenure of which the present work is carried out.

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