The search for alternative protein sources to replace soybean meal (SBM) is crucial for the sustainable development of aquaculture. This study investigated the effects of dietary replacement of SBM with Phaeodactylum tricornutum meal (PTM) on grass carp ( Ctenopharyngodon idella ) (65.00 ± 0.60 g). Five isonitrogenous and isolipidic diets were formulated, in which PTM replaced 0%, 25%, 50%, 75%, and 100% of SBM protein (denoted as PT0 to PT4). Fish fed diets PT2–PT4 showed significant improvements in specific growth rate (SGR) compared to the PT0 group after the 56‐day trial ( p < 0.05). All PTM groups exhibited significantly higher feed efficiency (FE) ( p < 0.05). Skin pigmentation was markedly improved, with significantly higher redness ( a ∗ ) and yellowness ( b ∗ ) values observed in fish fed PTM‐containing diets. Muscle nutritional quality was enhanced, as evidenced by significantly higher levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the PT3 and PT4 groups ( p < 0.05). Notably, nitrogen (N) and phosphorus (P) retention efficiencies were significantly elevated in the PT2–PT4 groups ( p < 0.05), indicating reduced nutrient discharge into the environment. Moreover, whole‐body lipid content decreased with increasing graded levels of PTM substitution, and plasma triglycerides (TGs) and cholesterol levels were significantly reduced in all PTM‐supplemented groups. Mechanistically, dietary PTM supplementation upregulated hepatic mRNA expression of lipolytic genes (peroxisome proliferator‐activated receptor alpha pparα , carnitine palmitoyltransferase 1 cpt1 , hormone‐sensitive lipase hsl , and adipose TG lipase atgl ) and downregulated lipogenic genes (fatty acid synthase fas , acetyl‐CoA carboxylase alpha acc , stearoyl‐CoA desaturase‐1 scd1 , and diacylglycerol O‐acyltransferase 1 dgat1 ), suggesting transcriptional regulation that enhances lipid catabolism and inhibits lipogenesis. In conclusion, PTM can effectively replace dietary SBM protein while simultaneously improving growth performance, skin quality, and nutrient utilization in grass carp and reducing potential environmental pollution. These findings confirm that PTM is capable of improving nutrient utilization and reducing N/P output. PTM therefore represents a promising alternative protein ingredient for developing eco‐friendly aquafeeds.
Qin et al. (Thu,) studied this question.