Abstract.— Brewer’s waste is one of the promising protein source by‐products for fish diets. A 10‐wk feeding trial experiment involving five different diets with increasing levels of brewer’s waste (32% crude protein) was carried out to evaluate the use of brewer’s waste in tilapia diets in place of fish meal. Growth performance was compared against a control diet formulated to have similar composition to a typical commercial diet. Four experimental diets replaced successively 25, 50, 75, and 100% of the fish meal protein with brewer’s waste. The diets were isonitrogenous and isocaloric. Results indicated that weight gain did not differ significantly (P > 0.05) with up to 50% replacement. Feed intake and utilization were depressed at high levels of brewer’s waste. In addition, methionine of high replacement level diets was low. The results of the digestibility trial demonstrated that the brewer’s waste used in this study has an apparent digestibility coefficient for protein of 70%. It was concluded that 50% of the fish meal protein in a typical commercial diet could be replaced with brewer’s waste with no adverse effect on growth and feed utilization for tilapia.
Tilapia is a warmwater fish and a popular choice for aquaculture. However, cold sensitivity of tilapia is a constraint to expansion of tilapia culture into the colder regions of the world. Tilapia generally require a thermal environment of 25-30 C. Acclimation to cold requires changes in gene expression such as delta 9 desaturase ( 9D) which is widely expressed in many poikilothermic animals in the process of cold acclimation. A major function of 9D is to desaturate membrane lipids in order to sustain membrane fluidity during cold. In this article we examined the effect of acute and chronic cold stress (12-14 C) on the expression of the 9D gene in muscle, gill, heart, and liver of growing Oreochromis niloticus. Despite the relatively cold temperatures, none of the fish were killed by the cold stress. Results indicate that there was no significant change in expression of 9D during acute cold stress. The expression of 9D in liver and heart tissues was not chronically affected by cold (7 d); however, 9D expression of muscle and gill tissue was increased in response to chronic cold stress. Muscle was the most responsive tissue demonstrating greater than 16-fold increase following 7 d of cold exposure. Unlike many other cold tolerant teleost fish, tilapia liver 9D transcription was not affected by acclimation to chronic cold stress. It is possible that upregulation of expression of 9D in muscle and gill tissue reflects the requirement of these tissues in maintenance of a higher metabolism associated with the need to sustain oxygen consumption, mobility, and heat generation. In contrast, reduced expression of 9D in liver may reflect lower overall metabolic rate during cold.
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