To compare the quality and nutritional differences of crayfish under freshwater and saline-alkali water aquaculture conditions, this study systematically analyzed the biochemical composition, physical properties, and nutritional evaluation of crayfish (Procambarus clarkii) cultivated in saline-alkali water (PC-SW) and freshwater aquaculture (PC-FW), respectively. The results showed that crayfish from PC-SW had higher crude protein, crude fat, water content, and ash content. At the same time, PC-SW had a higher meat yield (16.18 ± 0.74%) than PC-FW (p < 0.05), with no significant changes in the head weight ratio or hepatopancreas weight ratio, indicating superior crayfish quality. The trace element content of PC-SW differed significantly from that of PC-FW (p < 0.05), with the exception of Cu. To some extent, the amino acid and fatty acid compositions were similar. The no essential amino acids content of crayfish cultivated under freshwater and saline-alkali conditions was higher than the essential amino acids content. The total branched-chain amino acids (BCAAs) content was higher than the total aromatic amino acids (AACs) content in both groups; however, the BCAA to AAC ratio was similar, at approximately 2.14. The essential amino acid index results were 69.01 and 68.02, respectively. Finally, betaine and nucleotide concentrations increased and geosmin content was significantly reduced in PC-SW (3.13 ± 0.09 μg/kg) compared to PC-FW (4.32 ± 0.09 μg/kg) (p < 0.05), implying that PC-SW crayfish had a better flavor. Our findings revealed that cultivating crayfish under saline-alkali conditions can significantly improve the nutritional quality and flavor of muscle.

Salinity is one of the most critical environmental factors for fish, influencing their reproduction, growth, and physiological and metabolic activities. Lateolabrax japonicus is a major commercially important marine fish that has been widely cultured in China. However, there are few reports on the growth tolerance of fish juveniles of different species under various salinity conditions. In this study, we investigated the effects of acute low-salt stress on the survival, plasma osmolality, blood ion concentration, and Na⁺/K⁺-ATPase (NKA) activity in L. japonicus juveniles of two size groups. Our findings revealed no significant difference in survival rates between 5 cm and 10 cm juveniles at salinities of 0.2, 1, 3, 5, 10, 15, and 25. Plasma osmolality and blood ions exhibited a “decrease-increase-stabilization” pattern; 5 cm juveniles stabilized at 6 h at all salinities, whereas 10 cm juveniles required 48 h to stabilize at a salinity of 1, with isosmotic points of 10.91 and 11.00, respectively. Gill and kidney NKA activity followed an “increase-decrease-stabilization” pattern, with 5 cm juveniles achieving stability 12–24 h earlier than 10 cm individuals under low salinities (1, 3, 5). In conclusion, 5 cm L. japonicus juveniles exhibited superior low-salinity tolerance, accelerated osmoregulatory responses, and enhanced adaptation compared to 10 cm juveniles. These findings strongly support the prioritizing of smaller-sized L. japonicus for low-salinity aquaculture practices.

Free amino acids (FAAs) are important low-molecular-weight metabolites involved in osmotic regulation, acid–base balance, and nitrogen metabolism in fish exposed to saline–alkaline environments. To characterize tissue-specific FAA responses in mandarin fish (Siniperca chuatsi), 10 cm juveniles were exposed for 96 h to freshwater control (FW), salinity stress (S, salinity 8), alkalinity stress (A, alkalinity 20 mmol/L), or combined saline–alkaline stress (SA, salinity 8 + alkalinity 20 mmol/L). The contents of 19 FAAs were compared among plasma, muscle, liver, brain, and kidney. FAA profiles showed clear tissue specificity. Total FAA (17) decreased in plasma under all stress treatments, increased in muscle under S and SA but decreased under A, increased in liver and kidney, and decreased under single stress but increased under combined stress in brain. Distinct tissue distribution patterns were observed for functional FAA groups. Under salinity stress, osmoregulation-related FAAs, particularly Ala and Pro, showed higher contents mainly in muscle, liver, and kidney. Under alkalinity stress, kidney showed concurrent increases in multiple FAAs, including Ala, Pro, Glu, Gln, Val, Ile, and Leu, whereas brain was characterized by a high Gln content. Under combined saline–alkaline stress, liver was the main tissue in which multiple functional FAA groups increased simultaneously, kidney maintained elevated levels of several FAAs, and brain showed treatment-specific high levels of Gln and Tau. Redundancy analysis (RDA) indicated weak constrained explanatory power of salinity and alkalinity for the overall FAA profile, whereas tissue-specific differentiation was evident. Glu, Gln, and Pro showed directional consistency with the salinity vector, whereas Val and Leu tended to align with the alkalinity-related ordination direction. Overall, acute saline–alkaline exposure induced a functional and tissue-specific distribution pattern of FAAs rather than a uniform whole-body shift in mandarin fish.

To evaluate the nutritional enrichment effects of Euphausia superba meal on Moina mongolica Daday, different concentrations of krill meal (26, 39, 52, and 65 mg·L⁻¹) were applied as enrichment supplements, with non-enriched M. mongolica serving as the control. After a 6 h enrichment period, the compositions and contents of amino acids and fatty acids in M. mongolica were analyzed, and the astaxanthin content was simultaneously determined. The results showed that, compared with the control group cultured on a mixed diet of photosynthetic bacteria, yeast, and Nannochloropsis, enrichment with Antarctic krill meal at appropriate concentrations (26–39 mg·L⁻¹) markedly altered the fatty acid profile of M. mongolica. In particular, the levels of highly unsaturated fatty acids (HUFAs), including ∑ω6-PUFA and ∑ω3-PUFA, were significantly enhanced, with a pronounced increase in eicosapentaenoic acid (EPA). Furthermore, the total amino acid content, as well as the contents of six flavor-enhancing amino acids and ten essential amino acids for fish, were significantly higher in the enriched groups than in the control (p < 0.05). However, excessive supplementation of krill meal inhibited the growth of M. mongolica, suggesting a concentration-dependent effect. In addition, enrichment with whole Antarctic krill meal for 6 h did not significantly increase the astaxanthin content in M. mongolica, which may be related to the limited assimilation efficiency within the short enrichment duration. Overall, enrichment of M. mongolica with Euphausia superba meal at appropriate concentrations (26–39 mg·L⁻¹) effectively improves its fatty acid and amino acid composition, thereby enhancing its nutritional value as live feed for aquaculture larvae.

Saline and alkali aquaculture offers a sustainable strategy to alleviate pressure on freshwater resources and ecologically ameliorate saline and alkali environments; however, information regarding the quality of aquatic products from such conditions remains scarce. This study evaluated the nutritional components, color, texture, and flavor profiles of grass carp cultured under three representative saline and alkali conditions in China: carbonate (CB), chloride (CR), and sulfate (SF), with a freshwater-cultured grass carp (Ctenopharyngodon idellus) serving as a control (CK). The results obtained in our study showed that the CB group exhibited the lowest muscle water content (68.96 ± 0.04%). Crude fat and sodium levels were significantly elevated in all treatment groups compared to the CK group (p < 0.05). Conversely, the CK group displayed superior springiness and higher concentrations of geosmin, adenine, and uracil. Notably, the CR group exhibited the highest L* and whiteness values, whereas the CB and SF groups possessed significantly higher collagen content and enriched EPA and DHA levels. These findings demonstrate that saline and alkali conditions distinctly modulate the nutritional and flavor profiles of grass carp, highlighting their potential for producing value-added aquatic products under saline and alkali conditions.