The effects of high plant-based proteins (PP) used as alternative protein sources in aquafeeds on muscle cellularity and myogenic factors of rainbow trout, Oncorhynchus mykiss, remain unclear. This study explored muscle fibre growth phases and the impact of two additive mixtures (A) in high-PP diets on muscle physiology. Over a seven-month trial, 2000 fish (2·22 g) were divided into four groups (five replicates each) and fed isonitrogenous (fry, 46 %; fingerling, 44 %; and grow-out, 42 % crude protein) and isolipidic (20 % lipid) diets: control (30 % fishmeal), PP, PP + A1 (krill meal, taurine, selenium) and PP + A2 (proline, hydroxyproline, vitamin C). Sampling for muscle histology and myogenic gene expression was conducted at ten sampling points from Day 0 to Day 214. Muscle histology (fibre distribution: small, 0–20 μm; small-medium, 20–60 μm; large-medium, 60–100 μm and large, ≥ 100 μm diameter) revealed four growth phases: hyperplasia (2·2–15 g), hypertrophy (15–50 g), hyperplasia (50–150 g) and hypertrophy (150–350 g). MyoD2 and myogenic regulatory factor 4 (MRF4) were upregulated during hyperplasia, while myostatin 1 (MSTN1)/myostatin 2 (2) and reduced Paired box 7 indicating growth inhibition and fewer satellite cells. The PP diet without additives altered fibre recruitment, while PP + A2 enhanced hypertrophy, increasing large (> 100 μm) fibres. Additive mixtures modulated myogenic gene expression, with PP + A2 promoting MyoD2, myogenin and MRF4 and reducing MEF2A/C, contrary to known hypertrophy markers. PP + A1 and PP + A2 diets reduced MSTN1 expression, potentially mitigating growth inhibition. Additive supplementation in PP diets alleviates negative impacts on muscle cellularity and myogenic regulation. The identified growth phases provide insights for precision nutrition, supporting improved feeding strategies for sustainable aquaculture.

To alleviate the growth inhibition, and intestinal damage of Chinese mitten crab (Eriocheir sinensis) induced by low fishmeal diets (LF), an 8-week feeding trial was conducted to evaluate the addition of dietary soybean-derived bioactive peptides (SBP) in LF diets on the regulation of growth, digestion and intestinal health. The crabs were fed isonitrogenous and isoenergetic conventional diet and LF diets (10 % fishmeal replaced by soybean meal, LF) supplemented with 0, 1 %, 2 %, 4 % and 6 % SBP, respectively. The results showed that LF diet inhibited growth while inclusion of SBP quadratically remitted the growth inhibition induced by LF. For digestive function, increasing addition level of SBP quadratically improved the α-amylase and trypsin activities. For antioxidant function, LF group significantly increased the malondialdehyde content, while SBP linearly decreased the malondialdehyde level and cubically increased the anti-superoxide anion activity and total antioxidant capacity level. For intestinal health, the peritrophic membrane (PM) almost completely separated from the inner wall of the intestinal lumen, the epithelial cells reduced, the muscularis became thinner and the apoptotic signals increased in LF group; with SBP addition, the intestinal morphology was improved, with the PM adhering to the inner wall of the intestinal lumen, an increase in the number of epithelial cells and an increase in the thickness of the muscularis. Additionally, there was a decrease in apoptotic signals. Dietary SBP also increased the expression of PT and Crustin1 quadratically and decreased the expression of ALF1 linearly, ALF3 and ILF2 quadratically.

The present study investigated the effect of black soldier fly (Hermetia illucens) larvae meal (BSF) on haemolymph biochemical indicators, muscle metabolites as well as the lipid and glucose metabolism of Pacific white shrimp Litopenaeus vannamei. Four diets were formulated in which the control diet contained 25 % of fishmeal (FM) and 10 % (BSF10), 20 % (BSF20), and 30 % (BSF30) of FM protein were replaced with BSF. Four hundred and eighty shrimp (0·88 ± 0·00 g) were distributed to four groups of three replicates and fed for 7 weeks. Results showed that growth performance of shrimp fed BSF30 significantly decreased compared with those fed FM, but there was no significant difference in survival among groups. The whole shrimp crude lipid content, haemolymph TAG and total cholesterol were decreased with the increasing BSF inclusion. The results of metabolomics showed that the metabolite patterns of shrimp fed different diets were altered, with significant changes in metabolites related to lipid metabolism, glucose metabolism as well as TCA cycle. The mRNA expressions of hk, pfk, pk, pepck, ampk, mcd, cpt-1 and scd1 in hepatopancreas were downregulated in shrimp fed BSF30, but mRNA expression of acc1 was upregulated. Unlike BSF30, the mRNA expressions of fas, cpt-1, fbp and 6pgd in hepatopancreas were upregulated in shrimp fed BSF20. This study indicates that BSF20 diet promoted lipid synthesis and lipolysis, while BSF30 diet weakened β-oxidation and glycolysis as well as affected the unsaturated fatty acids synthesis, which may affect the growth performance and body composition of shrimp.

The present study aimed to measure tissue protein synthesis in sea bream fed isonitrogenous diets that contained 63, 55 and 50 % fishmeal; in the latter two diets, 16 and 27 % of the fishmeal protein was replaced with plant protein. Over a 35 d period, there were no differences in feed intake, growth or feed efficiency among the three diets. Protein metabolism was then measured in the liver and white muscle tissue as rates of protein synthesis and as the capacity for protein synthesis before feeding (0 h) and at different times after feeding (4–48 h). Diet did not have a significant effect on protein synthesis or on the capacity for protein synthesis in either tissue. The capacity for protein synthesis was not affected by time after feeding, and overall mean values were 81·02 (se 1·68) and 4·07 (se 0·94) mg RNA/g protein for the liver and white muscle, respectively. Liver and white muscle fractional rates of protein synthesis were significantly higher at 4–8 h, intermediate at 12 h and were not different among pre-feeding (0 h), 24 and 48 h. Overall, the indices of protein metabolism measured at various times over 48 h following feeding were closely aligned with measurements of feeding, growth and growth efficiency established over a longer time scale.