Growth and fatty acid composition of discus fish Symphysodon haraldi given varying feed ratios of beef heart, duck heart, and shrimp meat

Abstract

A 56 days experiment was carried out to examine the effects of nine different diets on the growth and biochemical composition of discus fish Symphysodon haraldi tissues. Nine different types of diets were created using three main ingredients (beef heart, duck heart, and shrimp meat) in varying proportions, i.e., 10:0:0 (F1), 9:0:1 (F2), 8:0:2 (F3), 6:2:2 (F4), 4:4:2 (F5), 2:6:2 (F6), 0:8:2 (F7), 0:9:1 (F8) and 0:10:0 (F9). As the proportion of beef heart within the diet decreased, the specific growth rates (SGR), length growth rates (LGR), and height growth rates (HGR) of S. haraldi first decreased (F1-F3), then increased (F4-F6), and thereafter decreased (F7-F9), while the feed coefficient rates (FCR) showed the opposite trend. No significant differences in SGR, LGR, HGR, and FCR between the F1 and F6 groups were observed. The survival rates decreased with lower beef heart levels. Dietary inclusion of beef heart and/or shrimp meat often resulted in a decrease of crude protein and ash content. Dietary fatty acids (FA) associated with the F3, F8, and F9 groups showed significantly lower concentrations of 18:3n-3 and 20:5n-3 relative to the other groups. Similarly, the F7 and F9 diets and the S. haraldi these diets were fed to demonstrated low and high 20:4n-6 levels, respectively. While the F1 and F9 diets were both poor in 22:6n-3, the F1 group showed significantly higher 22:6n-3 content than the F9 group, indicating the more efficient retention and/or bioconversion of this FA by S. haraldi in the F1 group. The results of this study suggest that shrimp meat might not necessarily be added into moist feed for S. haraldi culture. Diets with up to 60% duck heart could be achieved without affecting growth, but showed some negative influence on survival rates. Keywords: Symphysodon haraldi, Beef heart, Duck heart, Growth, Fatty acid