A team of Australian researchers found that cultivated large yellowtail kingfish (YTK, Seriola lalandi) perform better on 25% lipid diet at summer temperatures. The study, published in Aquaculture, shows an optimized diet design for both lipids and protein that can improve the YTK commercial production.

Seriola lalandi is a pelagic fish appreciated in the global fish market because of its excellent flesh quality. It is also a fast-growing species which makes it very suitable for aquaculture. YTK is also a thermosensitive fish, meaning that growth and feed efficiency can be affected outside the optimal thermal range between 20-25°C. 

Australian researchers, together with Ridley, assessed the optimum dietary protein and lipid levels for large YTK during a summer growing season. The team tested two series of diets with 25% and 30% lipids. Each series included three different diets with three different amounts of protein: 40, 44 and 48%. The six diets were tested in an 84-day experiment using 360 fish with an individual initial weight of approximately 2 kg. 

Results from final weight, biomass gain, SGR, and FCR indicated that fish fed the 25% lipids diets grew better than those fed the 30% lipids diets. Furthermore, the significant higher growth in fish fed on diet 1 (40% protein and 25% lipids) and on diet 2 (44% protein and 25% lipids) showed a better combination for large YTK raised in the summer.

Based on the combined results for 2-3.5 kg YTK from the trial, researchers suggested that the diet should contain at least 42.9% protein and 25.3% lipids. According to their results, the authors do not recommend using diet lipid levels of approximately 30% over summer periods. They emphasized that it would be uneconomical to formulate and manufacture diets containing higher protein and lipids levels.

Check out the study here.