Growth and protein digestibility of tambaqui, Colossoma macropomum, Cuvier 1818, fed diets based on fish silage

Bezerra, Andrea (2002) Growth and protein digestibility of tambaqui, Colossoma macropomum, Cuvier 1818, fed diets based on fish silage. Masters thesis, Memorial University of Newfoundland.

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Abstract

It is recognized that the cost of artificial fish feed makes a significant contribution to the costs of an aquaculture operation. In order to decrease the dietary costs an alternative protein source to traditional fish meal is needed. Silage is often used, however there is a lack of research on the utilization of silage as a main source of protein in fish diets in the Northeast of Brazil. Hence, this thesis was undertaken to determine the growth and apparent protein digestibility of tambaqui, Coiossoma rnacropomun, when fed diets based on formic acid and biological fermented silage compared to a control fishmeal diet. -- Fish silage was obtained by the addition of formic acid to minced tilapia, Oreochromis niloticus. Lactobacillus plantarum was used as inoculum and molasses as the carbohydrate source. Chemical composition, pH, total and free amino acid of the silages were determined. Formic acid and biologically fermented silage stored for 4 and 30 days were co-dried with wheat bran and incorporated into the diet of juvenile tambaqui as the main source of protein. The control diet was formulated using fishmeal as the main source of protein. The 5 experimental diets and the control diet were isocaloric and isonitrogenous. -- The growth experiment used fifteen round concrete tanks (3 for each diet) with 15 fish per tank. Fish were fed twice a day at a rate of 3% of body weight. The fish were weighed every 15 days to determine the amount of food to be given, and to calculate growth parameters such as; average daily gain, specific growth rate, feed conversion rate and protein efficiency rate. Fifteen aquaria were used for the digestibility experiment. Each aquarium was stocked with 5 juvenile tambaqui. Chromic oxide was used as a marker and feces were collected from the bottom of the water column twice daily. -- Results showed that both acid and biological silages had good storage properties. The variations in moisture, protein, lipid and ash between the four silages (formic acid silage stored for 4 and 30 days and biological silage stored for 4 and 30 days), that were included in the fish diets, did not induce any significant change in the amino acid profile of silage diets and the amino acids requirements for tambaqui were met. Although formic acid silage, stored for 4 and 30 days, showed higher protein solubilization and higher levels of free amino acid at the end of the 30 days storage period compared to the biologically fermented silage, there was no significant difference in growth and digestibility between treatments. -- Based on the excellent acceptability of all diets tested by juvenile tambaqui, good protein digestibility and the satisfactory growth performance obtained in this study, we concluded that co-dried tilapia fish silage could be successfully utilized as an alternative protein source for fishmeal in fish diets. In this way, it is possible to utilize processing wastes for producing valuable animal protein and, furthermore, make a contribution to the protection of the environment.

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