by
HANS MANN
Bundesforschungsanstalt für Fischerei
Hamburg, Federal Republic of Germany
Abstract
The utilization of protein and of cellulose by tilapia was determined by using the aquatic plants, Spirodela polyrrhiza and Elodea canadensis. The utilization of protein was between 42 and 57 percent and that of crude fibre between 43 and 68 percent.
L'UTILISATION DES ALIMENTS PAR LE TILAPIA MELANOPLEURA, DUM.
Résumé
La capacité d'assimilation des protéines et de la cellulose des tilapia a été déterminée au moyen d'expériences avec les plantes aquatiques Spirodela polyrrhiza et Elodea canadensis. L'assimilation des protéines varie entre 42 et 57 pour cent et celle des fibres brutes entre 43 et 68 pour cent.
EL APROVECHAMIENTO DEL ALIMENTO POR TILAPIA MELANOPLEURA, DUM.
Extracto
El aprovechamiento de proteínas y celulosa por la tilapia ha sido determinado utilizando las plantas acuáticas, Spirodela polyrrhiza y Elodea canadensis. El aprovechamiento de proteína fué del 42 al 57 por ciento, y el de fibra bruta entre el 43 y el 68 por ciento.
Species of tilapia are widely cultivated in many countries of the world. Two of the more commonly used species are Tilapia mossambica and T. melanopleura. T. mossambica is omnivorous, whereas T. melanopleura feeds on plants. Examination of stomach contents has shown the nature of food consumed by them, but this information alone is not sufficient to designate the value of each food item. It is of great importance to know how the consumed food is being utilized. To solve such questions many experiments have been conducted (Chimits, 1957; Huet, 1960), but unfortunately we do not have evidence to show to what extent each food component is being digested and utilized by the fish.
The most important component of food is protein, which makes it possible to assess the nutritive value of foodstuffs to a certain degree by the measurement of its content of digestible nitrogen. Vegetable foodstuffs always consist to a certain degree of cellulose, and this component too is of importance for estimating nutritive values. Therefore in the present work the utilization of protein and of cellulose by Tilapia are the main points considered.
The species chosen for the experiments was Tilapia melanopleura Dum. and each speciman was kept separately in a glass aquarium at 27°C. The water was well oxygenated. Based on previous experience of how much food the fish is able to eat, a weighed quantity of food was given to the fish. About one hour later the rejected food was removed and weighed, and the faeces were gathered for analysis. As the chemical composition of the food, mainly protein and cellulose, was known it was possible to tell the nutritive value of the consumed food from the quantity of these constituents in the faeces.
The analysis of crude protein was done by the procedure of Kjeldahl. The conversion of nitrogen to crude protein (in milligrams) was done by multiplying by the factor 6.25 (Mann, 1935). Crude fibre was determined by the well known Weender procedure.
Tilapia melanopleura feeds on plants. From the fry stage to a size of 3 to 5 cm it feeds on phytoplankton and unicellular algae, after which it prefers plants such as Sparganium, Chara, Potamogeton, etc. It eats artificial food only after having reached the size of 4 cm.
As it was not possible to conduct a quantitative feeding experiment with phytoplankton the study was limited to the higher plants. Spirodela polyrrhiza and Elodea canadensis were used for the experiments and their composition is given in Table I.
Table I
Composition of the aquatic plants used for feeding Tilapia melanopleura
| water % | protein % | fat % | crude fibre % | |
| Spirodela polyrrhiza | 96.7 | 0.6 | 0.008 | 1.03 |
| Elodea canadensis | 90.9 | 2.1 | 0.02 | 3.09 |
The fish digested its food rapidly because of the high water temperature (27°C). The last faeces appeared after 24 to 27 hours. The most abundant defaecation was noticed after 12 to 15 hours. When examining the faeces under a microscope one could still recognize the structure of the cells. The utilization of protein from both plant foods was between 42 and 57 percent (average 53 percent). The digestion of crude fibre, however, differed; the tilapia using 52–68 percent (average 64 percent) of the crude fibre from Spirodela, but only 43–55 percent (average 49 percent) of that from Elodea (Table II).
Table II
Utilization of food by Tilapia melanopleura
| protein % | crude fibre % | |
| Spirodela polyrrhiza | 42 – 55 | 52 – 68 |
| Elodea canadensis | 43 – 57 | 45 – 55 |
In previous experiments it had been found that carps and other cyprinids utilized from 80 to 95 percent of the nitrogenous material in their food (Mann, 1935; 1948). The digestion of lupin protein by carp was extremely high, 95 to 98 percent (Mann, 1938) compared with the 53 percent utilization by tilapia.
The utilization of crude fibre by carp from maize, lupin or rye varied from 20 to 90 percent according to the nature of the foodstuff.
Chimits, P., 1957 The tilapias and their culture. A second review and bibliography. FAO Fish. Bull., 10(1):1–24
Huet, M., 1960 Traité de pisciculture. Bruxelles, Ch. de Wyngaert. 369 p.
Mann, H., 1935 Untersuchungen über die Verdauung und Ausnutzung der Stickstoffsubstanz einiger Nährtiere durch verschiedene Fische. Z.Fisch., 33:231–74
Mann, H., 1938 Der Futterwert verschiedener Lupinenarten (Bitterlupine und Süsslupine). Allg.Fisch.-Ztg., 64:3–7
Mann, H., 1948 Uber die Rohfaser-Verdauung des Karpfens. Arch.FischWiss., 1:1–11
