NUTRITIONAL STATUS ON STRESS TOLERANCE OF FISHES WITH DIFFERENT FORAGING MODES

To investigate the effects of nutritional status on stress tolerance in fish with different foraging modes, this study selected ambush foragers: largemouth bass (Micropterus salmoides, Perciformes), southern catfish (Silurus meridionalis, Siluriformes), bass carp (Percocypris pingi, Cypriniformes) and active foragers: tilapia (Oreochromis niloticus, Perciformes), yellow catfish (Pelteobagrus fulvidraco, Siluriformes), Qing bo (Spinibarbus sinensis, Cypriniformes) as research subjects, assigned them to starvation group (fasted for 14d), starvation control group (fasted for 24h), digestion group (sampled 1h after satiation feeding), and digestion control group (fasted for 24h), and measured hypoxia tolerance indices, including critical metabolic rate (ṀO_2PCRIT), oxygen supply capacity (α), and critical oxygen tension (P_CRIT), as well as thermal tolerance indices, i.e., critical thermal maximum (CT_MAX) and critical thermal minimum (CT_MIN). The results showed that the effect of nutritional status on hypoxia tolerance mainly depended on foraging mode. Starvation induced parallel decrease in ṀO_2PCRIT and α in all species, with greater decrease in active foragers, ultimately maintaining P_CRIT stable. The two siluriform species, which naturally inhabit slow-flowing or silty bottom environments and frequently suffer from combined hypoxia and food shortage, exhibited a significant decrease in P_CRIT after starvation (P<0.01), indicating enhanced hypoxia tolerance. Digestion caused a larger increase in ṀO_2PCRIT in active foragers, while α remained nearly unchanged, resulting in a higher increase in P_CRIT in active foragers than in ambush foragers, i.e., a greater impairment of hypoxia tolerance after feeding. The effect of nutritional status on thermal tolerance primarily depended on phylogenetic background. When nutritional status changed, siluriform fishes showed the strongest thermal response: both CT_MAX and CT_MIN decreased significantly after starvation (P<0.05), and only CT_MAX of southern catfish decreased significantly after digestion (P<0.001). In perciform fishes, CT_MAX decreased significantly after starvation (P<0.01), while CT_MIN showed significant differences after digestion (P<0.05). In cypriniform fishes, thermal responses were the most conservative, with only CT_MIN showing significant differences after starvation (P<0.05). These findings reveal the physiological adaptation strategies of fishes with different foraging modes in response to food resource fluctuation and environmental stress, providing a theoretical basis for understanding the response potential of fishes with different foraging modes to environmental changes in natural waters.