The nutrition and feeding of a native Thai species, the marble goby (Oxyeleotris marmoratus), involving on-farm and experimental studies

Abstract

In Thailand, culture and production of a high value freshwater fish, the marble goby, is dependant upon farm-made feeds using marine and freshwater trash fish as primary ingredients. However, there is lack of nutritional research regarding the use of such farm-made feeds and their impacts on the nutritional status, growth and health of marble goby. The aims of the present study were to evaluate the effects of farm- made feeds on slaughter indices, fish lipid classes and fatty acid profiles, nutrient composition and digestibility. In addition it was intended to improve on-farm feed quality for both current practical feeds as used by farmers and alternative feeds using rice bran and tilapia with reference to biochemical composition, growth performance and haematology of marble goby.

Nutritional evaluation of farmed fish compared to their wild counterparts indicated that fatty acid composition of farmed marble goby was markedly influenced by diet. Marble goby appeared to utilize MUFA preferentially as an energy source compared to SFA. Fish muscle was characterised by higher n-6 PUFA; arachidonic acid (20:4n-6, AA) and docosapentaenoic acid (22:5n-6, DPA). Eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22: 6n-3, DHA) comprised the majority of n-3 PUFA found in fish muscle and can potentially be enriched into marble goby muscle through the diet. The significantly higher ratios of neutral liver lipid to polar lipid (NL/PL) indicated the imbalance of dietary lipid and energy of on-farm feeds. Moreover, findings on slaughter indices and lipid peroxidation of farmed fish; higher HSI, VSI, liver TBARS and the pale lipid-rich liver of farmed fish indicated problems with the nutritional quality of lipid in farm-made feeds.

Experiments aimed to improve farm-made feeds using supplemental vitamin E in the form of α-tocopherol. These demonstrated that supplementation of α-tocopherol to oxidised diets, both mackerel and tilapia based, did not result in a significant beneficial effect in reducing mortality, and improving growth and haematology in marble goby. However, dietary α-tocopherol supplementation helped in reducing fish muscle peroxidation but was not related to muscle α-tocopherol levels. In mackerel based diets containing lipid peroxidation up to 250-300 µmols MDA g-1, α-tocopherol supplementation appeared not to help in reducing liver peroxidation.

The alternative use of tilapia as a feed for marble goby resulted in growth and survival rates similar to those of fish fed mackerel based diets. Tilapia contained intrinsic α-tocopherol levels that appeared to be sufficient to reduce marble goby tissue peroxidation. The synergic effects on antioxidant activities between α- tocopherol supplement and natural E vitamer contained in rice bran helped to reduce tissue TBARS and improve haematology in fish fed combination diets of oxidised tilapia and rice bran.

The inclusion of rice bran in farm based diets resulted in decreased tissue peroxidation, an adverse affect on dry matter and protein digestibility; and lower fish feed intake, growth and survival rate when 25% of rice bran was added into practical mackerel based diet. Overall, formulated feeds showed promising growth and survival rate in marble goby but more research on dietary nutrients and energy balances are required.