Spatial Optimization in Recirculating Aquaculture Systems: Cortisol-Mediated Growth Modulation and Polyunsaturated Fatty Acid Enrichment in Carassius Auratus VAR. Pengze

Abstract

This study systematically evaluated the effects of tank volume optimization in a recirculating aquaculture system (RAS) on growth performance, physiological responses, and nutritional quality of Carassius auratus var. Pengze. Three spatial experimental groups (0.3 m3(L), 0.15 m3(M), 0.075 m3(S)), with 4 parallel tanks in each experimental group, and all the rearing tanks are part of one RAS with shared water treatment processes. Juveniles (initial body weight 20.13 ± 0.52 g) were stocked at 2.68 kg/m3 density for 100 days to assess space-size effects on zootechnical parameters and physiological indices. Key findings revealed: (1) Group S exhibited 26.4% higher weight gain rate (209.68 ± 10.16%) and 15.3% greater specific growth rate (1.13%/d) compared to Group L (p<0.05p<0.05), with minimized weight coefficient of variation (14.65% vs. 20.59% in Group L). Ontogenetic analysis identified phased growth patterns, with Group S dominating early-stages (0–60 days) and Group L excelling in later phases (80–100 days); (2) Serum cortisol levels followed a spatial gradient (S: 604.03 ± 28.01 pg/mL < Group L: 1021.57 ± 31.30 pg/mL < Group M:1405.97±60.05pg/mL; p<0.05), while lipid metabolism markers (triglycerides, total cholesterol) peaked in Group S; (3) Proximate muscle composition showed nonsignificant variation (p>0.05) in moisture, ash, and crude protein. Group S demonstrated elevated crude fat content (1.40 ± 0.11%). Muscle lipidomics demonstrated Group S superiority in health-beneficial fatty acids, with 183% higher highly unsaturated fatty acids (HUFAs) and 126% elevated n-3 polyunsaturated fatty acids (PUFAs) versus Group L (p<0.05p<0.05). These findings suggest that restricted culture volume (0.075 m3) optimizes growth performance in juvenile Carassius auratus var. Pengze (∼20 g), while potentially inhibiting development in larger specimens (>40 g). Space constraints appear to modulate cortisol secretion, lipid metabolism, and HPT-axis regulation, providing critical insights for RAS optimization in phased culture systems.

Keywords: Recirculating aquaculture system, Culture volume optimization, Carassius auratus var. Pengze, Growth physiology, Stress biomarkers