Dietary composition manipulation to enhance the performance of juvenile barramundi (Lates calcarifer Bloch) reared in cool water

Abstract

Barramundi Lates calcarifer reared in cool water (202 2 1C) grow slowly and feed is used poorly compared with ¢sh in warm water (28^32 1C). Two comparative slaughter growth assays were carried out with juvenile barramundi to see if increasing the digestible energy (DE) and/or the n-3 highly unsaturated fatty acid (n-3 HUFA) content of the feed would improve growth of ¢sh raised in cool water. Increasing the DE content of the feed from 15 to 17 or 19 MJ kg À1 while maintaining a constant protein to energy ratio in Experiment 1 brought about signi¢cant improvements in feed conversion ratio (FCR) (from 2.01 to 1.19) and daily growth coe⁄cient (DGC; from 0.69 to 1.08%/day) for ¢sh at 20 1C. For ¢sh at 29 1C, improvements, while signi¢cant, were of a lesser magnitude: from 1.32 to 0.97 for FCR and from 3.24 to 3.65%/day for DGC. Increasing the absolute amount of dietary n-3 HUFA, expressed as the sum of eicosapentaenoic and docosahexaenoic fatty acids, from 0.5% to 2.0% in Experiment 2 improved DGC linearly and FCR curvilinearly for ¢sh at 29 1C whereas at 20 1C, DGC was not a¡ected while FCR improved slightly (from1.83 to 1.68). Feed conversion ratio was optimized with a dietary n-3 HUFA of about 1.5%. Providing barramundi with a feed that is high in DE (viz 19 MJ kg À1 ) and a digestible protein to DE ratio of 22.5 g MJ À 1 is a practical strategy for improving the productivity of barramundi cultured in cool water whereas increasing dietary n-3 HUFA conferred very little additional bene¢t.

Marginal efficiencies of long chain-polyunsaturated fatty acid use by barramundi (Lates calcarifer) when fed diets with varying blends of fish oil and poultry fat

“…In this study, FO substitution with PF covered a range of LC-PUFA inclusion from 22.0 to 4.8 g/kg, theoretically surpassing the reported minimum requirement of 12 g/kg LC-PUFA (Williams et al, 2006). It is noteworthy that this species is a catadromous, obligate carnivore and the reduced levels of LC-PUFA fed in this study should probably have induced a range or EFA deficiency symptoms similar to those previously reported (Catacutan and Coloso, 1995;.…”

“…Until recently, variable responses to fish oil replacement and fatty acid requirement studies have led to further questions being raised about lipid metabolism in this species (Catacutan and Coloso, 1995;Morton et al, 2014;Raso and Anderson, 2003;Williams et al, 2006). The fish in this study achieved a minimum 2.5-fold increase in weight over the twelve week study period.…”

“…The barramundi (Lates calcarifer), also known as the Asian seabass, is an obligate carnivorous fish central to an expanding aquaculture industry in the Indo-Pacific region with a reported long chain-polyunsaturated fatty acid (LC-PUFA) requirement in juvenile fish of around 1.2% (Williams et al, 2006). However, variable responses of barramundi to FO replacement studies have led to questions being raised about the upper limits of FO substitution in this species Morton et al, 2014;Raso and Anderson, 2003;Tu et al, 2013).…”

“…Depletion of LC-PUFA in the diet of barramundi can potentially lead to reduced productivity and the onset of essential fatty acid deficiency symptoms (Catacutan and Coloso, 1995;Williams et al, 2006). Moreover, a lack of dietary LC-PUFA will also likely be reflected in the flesh, diminishing the human nutritional value of the product (Turchini et al, 2009).…”

“…It was hypothesised that barramundi would reach a critical limit of FO substitution when absolute levels of dietary LC-PUFA dropped below estimated requirement of around 1.2% (Williams et al, 2006). Therefore a series of diets were developed to examine the effects of diluting fish oil with poultry fat on the growth and feed utilisation performance of juvenile barramundi and to determine the consequences of this on the fillet fatty acid profiles.…”