Investigation of possibilities of using distiller's dried grains with solubles in feed of juvenile rainbow trout (Oncorhynchus mykiss Walbaum, 1792)

In this study, two different feeding trials was performed to investigate inclusion levels of distillers dried grains with solubles (DDGS) as a fish meal and soybean meal replacement for juvenile rainbow trout (Oncorhynchus mykiss). In scope of this research; growth, feed assessment, economic assessment, chemical composition of fish meat, digestibility rates of nutrients of experimental diets, histology of liver and intestine are studied. In the first trial, four different experimental diets are prepared which have equal protein (45.47% crude protein) and energy (4164 kcal/kg digestible energy) values, by using DDGS feed in rates of 0%, 10%, 20% and 30% (Control, DDGS10, DDGS20 and DDGS30) in stead of the reducing fish meal. Fish whose starting weights are 19.88 began to be fed with the prepared experimental diets for 84 days. At the end of trial, the highest live weight increase, percentage live weight increase, specific growth rate and thermal growth coefficient values are found in DDGS30 group. While feed conversion and protein efficiency rate values are similar among the experimental groups, it is seen that DDGS30 group has the highest feed consumption values and there is no significant difference between the other groups. Feed price reduces significantly depending upon DDGS increase in feed. While economic efficiency ratio reduces depending upon DDGS increase in feed, economic profit index increases; these intergroup reduce and increases are found important statically (P<0.05). Difference is insignificant between values of nutrient digestibility rate of intergroup experimental feeds and chemical composition of fish meat. At the end of histological analyses, it is seen that there is no significant difference in diameter of cell nucleus in liver however there is an amount of vacuolization in hepatocyte cell cytoplasm of fish in DDGS20 and DDGS30 groups and some of hepatocyte cell nucleuses are not in central position. As a result of histomorphometric measurements, it is detected that DDGS used in feed has no significant effect on villus heights in the distal intestines of fish, submucosa, stratum compactum and muscular layer thicknesses however DDGS caused by expansion of the lamina propria. In the second trial, it is examined the effects on fish of using DDGS in stead of reducing soybean meal in feed. Two different controls are prepared as of Control-1 diet containing only fish meal as a protein resource in Trial-2 and Control-2 diets containing fish meal and soybean meal. The other experimental diets, totally five different diets are prepared (Control-1, Control-2, DDGS33, DDGS66 and DDGS100) which have equal protein (45.47 crude protein) and energy (4164 kcal/kg digestible energy) values by using DDGS in stead of 0%, 33%, 66% and 100% of soybean meal amount in Control-2 diet. Fish whose starting weights are 20.46 began to be fed with these prepared experimental feeds for 84 days. At the end of trial, the highest live weight increase, specific growth rate and thermal growth coefficient, feed conversion rate, protein efficiency rate are found in fish of DDGS66 group that DDGS is used in rate of 20% in diet in stead of reducing soybean meal. No statistically significant difference is seen between the value of intergroup survival rates, condition factor, hepatosomatic index and visserosomatic index. With the reduce of soybean meal rate and increase of DDGS in diet, feed price cost reduces significantly. The best economic efficiency ratio and economic profit index values are seen in DDGS66 and DDGS100 groups among them. A similarity is found between the values of nutrient digestibility rates of experimental diets and the values of chemical composition of fish meat. As a result of histological analyses, it is detected that there is no statistically significant difference in diameter values of cell nucleus in liver however there is an amount of decrease in diameter of cell nucleus in liver with the increase in usage of plant protein resource in diet. It is detected that there is an amount of vacuolization in hepatocyte cell cytoplasm of fish from groups except for Control-1 and some of cell nucleuses are not in central position. As a result of histological analysis, it is detected that there are visible negative changes in other groups in comparison to villus form of fish from Control-1 group. As a result of histomorphometric measurements, it is detected that there is an increase in lamina propria, submucosa and muscular layer thicknesses of fish fed by Control-2 and DDGS33 diets in comparison to DDGS66 and DDGS100 groups (P<0.05). At the end of this thesis study, it is concluded that DDGS can be used up to the rate of 30% in diet of juvenile rainbow trout as per the result of trial-1 and it can be used in stead of the whole soybean meal as per the result of Trial-2.