The Hot-Water Extract of Sargassum sp. as a Feed Ingredient for Spotted Scat (Scatophagus argus Linnaeus, 1766) Reared in Songkhla Lake: Effects on Growth, Feed Efficiency, Hematological Data and Body Composition

Abstract

The growth performance of Scatophagus argus (25.53 ± 0.89 g) reared in Songkhla Lake, a brackish lagoon, was evaluated after feeding isonitrogenous and isocaloric diets containing hot-water extract from a seaweed, Sargassum sp., at 0, 0.25, 0.50, 0.75 or 1 g·kg−1. Triplicate groups of fish were reared in 15 net cages (50 × 50 × 60 cm) at a density of 20 fish per cage, and the diets were fed twice a day at a rate of 5% of fish body weight per day for 8 weeks. The final body weight, weight gain (WG), average daily gain, and feed intake (FI) showed significant positive and quadratic responses to the Sargassum extract level. The highest WG (57.97%) and FI (0.34) were recorded in the fish that received the hot-water extract at 0.25–0.5 g·kg−1 of diet. The protein efficiency ratio showed significant positive linear and quadratic responses to the Sargassum extract level, while the hepatosomatic index showed a significant positive linear response to the Sargassum extract level. The body protein and ash contents showed positive, linear and quadratic responses to the Sargassum extract level, and the highest crude protein (49%) was observed in the 0.5 g·kg−1 diet group. There were no significant effects of the Sargassum extract levels on feed conversion ratio, food conversion efficiency, lipid and moisture contents, survival rate, hematocrit, and white or red blood cell counts. However, hematological data between fish in the control group and the Sargassum extract groups tended to be different. Overall, the optimum level of seaweed-extract supplementation for spotted scat under natural conditions was determined to be approximately 0.5 g·kg−1 diet.