An acute elevation in temperature impacts fish physiology and in turn causes an alteration in growth performance. This study investigated the effect of acute thermal stress on skeletal muscle growth and quality in gibel carp (Carassius gibelio). The gibel carp were randomly assigned to three temperature treatments, 20 °C, 26 °C, and 32 °C, for 168 h. The muscular quality characteristics and the expressions of the genes related to muscle growth were assessed at 0 h, 1 h, 12 h, 24 h, 72 h, and 168 h. The muscle nutrient content was significantly higher in the 20 °C treatment, and the muscle was more tender and elastic. The gene expression levels of the MRFs family were significantly upregulated and then gradually decreased after 1 h. The expression level of MSTN-2 was increased in the 32 °C treatment at 168 h, in support of the slow growth rate under acute thermal stress. It is implied that gibel carp could adapt to acute thermal stress to a certain extent. Acute thermal stress, however, eventually led to a decrease in muscle growth rate and quality.

The land-based recirculating aquaculture system (RAS) has been widely applied to fish farming as a new eco-friendly culture model. This system consists of circular culture tanks on land integrated with water treatment and recycling systems. This study investigated the growth performance of juvenile gibel carp (Carassius gibelio) cultured at high stocking density (HSD, 0.3 kg/m³) and low stocking density (LSD, 0.15 kg/m³) conditions in RAS, and evaluated the comprehensive economic profit of RAS. The body weight, body length, weight gain rate, and condition factor of gibel carp in the LSD group were significantly higher than those in the HSD group (p < 0.05). The feed conversion ratio increased significantly in the HSD group (p < 0.05). A histological analysis revealed a significantly higher density of white muscle fibers in the LSD group (p < 0.05). Relative mRNA expression levels showed that ubiquitin–proteasome system (UPS)-related genes, ub, psma2, and mafbx, were significantly expressed in the HSD group, while the s6k1 expression was elevated in the LSD group (p < 0.05). The mRNA expression levels of keap1 and hsp70 in the dorsal muscle were significantly higher in the HSD group (p < 0.05). Throughout the rearing period, the water temperature remained consistent between the two density groups. The pH value gradually decreased and the dissolved oxygen levels in the HSD group were generally lower than in the LSD group. The nitrite nitrogen (NO₂⁻-N) content was higher in the HSD group. Compared to the LSD group, the return on investment was significantly lower in the HSD group. In conclusion, the water quality and growth rates of juvenile gibel carp were better in the LSD group. An appropriate stocking density improved the growth performance and aquaculture economic efficiency.

This study investigated the effect of a lotic environment on morphological characteristics and energy metabolism in juvenile grass carp Ctenopharyngodon idella. The fish were stocked in the lotic environment and forced to swim for 12 h per day for 4 weeks at three water current velocities of 0.5, 2, and 4 body length s⁻¹ (Bl s⁻¹). The control fish were stocked in the lentic environment with water current velocities of 0 Bl s⁻¹. The results showed that lotic environment significantly increased body weight, body length, and condition factor of grass carp. The first principal component (PC1) characterized by measured overall body size suggested that fish in a lotic environment had body stoutness and wider tail stalk. Standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic swimming performance (U_crit) were elevated with the increased water flow and positively correlated with PC1. The 4 Bl s⁻¹ group showed significantly decreased contents of serum glucose and muscular glycogen, and a significantly increased level of serum lactic acid. The mRNA expression levels of AMP-activated protein kinase-phosphorylate PPAR γ coactivator 1 α-nuclear respiratory factor 1 (AMPK-PGC1α-NRF1) pathway-related genes were significantly upregulated in red muscle of grass carp in the lotic environment. Water flow environment at 4 Bl s⁻¹ significantly increased ratios of metabolic enzymes (lactate dehydrogenase/citrate synthase) and cytochrome c oxidase/citrate synthase) in the muscle. The relationship between morphological characteristics and metabolic capacity suggested that the body size of grass carp in a lotic environment was shaped to promote energy metabolism. The study identified the evidence of the mechanism and relationship of the trade-off between energy and morphology in grass carp.

The impact of the living environments on the intestinal microbiota of Gymnocypris potanini firmispinatus was studied by analyzing intestinal microbiota diversity, composition, and potential function among wild, domesticated, and cultured groups. The results showed that the fish living in the wild environment exhibited the highest alpha diversity of intestinal microbiota. Intestinal microbial communities in the three groups clustered by living environment, with domesticated and cultured groups showing higher similarity. The dominant phylum in the wild group was Proteobacteria, whereas Fusobacteria and Proteobacteria were the predominate bacteria in the domesticated and cultured groups. RsaHF231, Actinobacteria, Fusobacteria, Cyanobacteria, and Firmicutes were the five key bacteria differentially expressed among the groups. Functional prediction revealed significant variation in the L-cysteine degradation III pathway (PWY-5329) between wild and domesticated groups, and in the vitamin E biosynthesis pathway (PWY-1422) between wild and cultured groups (p < 0.05). These findings highlight the differences in microbiota communities between wild and farmed fish, which are essential for enhancing the cultivation of G. p. firmispinatus and for the formulation of specific probiotics and functional feeds.