Effect of Dietary Lipid Level on Growth Performance of Splittail at 18°C

A 12‐week feeding trial was conducted to study the effect of dietary lipid level on growth performance of juvenile Sacramento splittail Pogonichthys macrolepidotus at 18°C. We selected this temperature to simulate their natural habitats, although an earlier study showed that their optimum temperature was 22–26°C. Six isonitrogenous and isoenergetic purified diets were formulated to contain 2–12% lipid in 2% increments, and dietary lipid was an equal mix of corn oil and cod liver oil. Fish with an average initial body weigh of 9.0 ± 0.2 g (mean ± SE, n = 24) were kept in a 24‐tank, flow‐through system with 15 fish per tank, and each diet was randomly assigned to four replicate tanks of fish. Fish were fed 3.0% of their body weight per day by automatic feeders, which dispensed a small amount of feed every few minutes in daylight hours. Body weight and feed efficiency increased significantly with increasing dietary lipid level up to 8%. Fish fed the diet containing 8% lipid showed significantly higher body weight increase and feed efficiency than those fed the diets containing less than 6% lipid. Dietary lipid level did not affect the hepatosomatic index, condition factor, and intraperitoneal fat ratio. Whole‐body moisture was significantly lower but lipid was higher in fish fed the diet containing 8% lipid than in those fed the diets containing less than 6% lipid. Histological analysis revealed a higher prevalence of hepatocellular fatty vacuolation in fish fed the diet containing 12% lipid. Based on a broken‐line analysis, a dietary lipid level of 8.4% is recommended for juvenile splittail reared at 18°C.