Dietary starch level affects nutrient digestibility, faecal waste production and characteristics in yellowtail kingfish (Seriola lalandi) depending on the level of fish meal replacement

Yellowtail kingfish have a poor faecal integrity when fed with pelleted diets which may be due to the presence of dietary starch. Moreover, whether dietary starch interacts with plant protein ingredients, is not known. In this study, we investigated the effect of dietary starch level, protein source and their interaction effect on faecal waste production and characteristics (visual appearance, faecal removal efficiency and particle size distribution (PSD)). Four diets were formulated according to a 2 × 2 factorial design (starch level × protein source). The effect of starch level was tested by either including 0% (LS - low starch, 4% starch) or 20% gelatinized wheat flour (HS - high starch, 20% starch). FM diets contained fish meal as protein source, whilst at FM/P diets approximately 65% of the fish meal was replaced by plant protein ingredients. Twelve tanks were stocked with 21 fish (mean initial weight 53 g) and fish performance, nutrient digestibility, faecal waste production and characteristics were evaluated over a 36-day experimental period. Both starch level and protein source affected the organic matter digestibility (p 0.05). Growth was similar between the FM and FM/P at low starch diets (p