Rising ambient water temperatures present severe physiological and metabolic challenges to captive teleost, impacting digestive efficiency, energetic demand, and endocrine dynamics. Understanding these temperature-dependent responses is essential for optimizing aquaculture management and conserving species under climate change. This synthesis evaluates the physiological mechanisms of orangefin labeo (Labeo calbasu) and Malabar blood snapper (Lutjanus malabaricus) across thermal regimes ranging from 22℃ to 34 ℃.

Diagnostic X-radiography in hybrib groupers (Epinephelus spp.) demonstrates that elevated temperatures accelerate gastric emptying time, shortening complete gut clearance from 17 h at 22 ℃ down to 13h  at 34 ℃. Respirometry evaluations on juvenile Lutjanus malabaricus parallel this trend: oxygen consumption rates (MO2) and respired energy increase significantly with water temperature, rising from 3.07 ± 0.04  mg O2 h -1 (183.31 ± 12.70 J h-1) at 22 ℃ to 5.56 ± 0.16 mg O2 h -1) (332.17±10.99 J h -1) at 34 ℃. However, hyper-accelerated transit and elevated metabolic maintenance costs at extreme temperatures do not translate to improved digestive or growth performance.

In Labeo calbasu, gastric pepsin activity follows an asymmetric thermal threshold, peaking sharply at 30℃ (8.34 ± 0.71 U 37 mg protein -1) before experiencing thermal denaturation and instability at 34 (5.14 ± 1.09 U 37 mg protein -1). This enzymatic peak mirrors somatic growth

metrics in L. calbasu, where the species exhibits its maximum specific growth rate (SGR: 0.45 ± 0.05% day -1) and weight gain (3.07±0.70 g) at 30℃. Systemic endocrine profiling in L. calbasu further confirms this optimal thermal range: key reproductive hormones—follicle-stimulating hormone (FSH:1.45 ± 0.10 mIU mL -1), luteinizing hormone (LH:1.61 ± 0.04 mIU mL-1), serum testosterone (1.50 ± 0.01 ng dL -1), and estradiol-17β (E2 :54.3pg mL -1) peak at 30 ℃  , but are suppressed at 22 ℃ and 34 ℃ . Correspondingly, temperature quotient (Q 10) analysis for L. malabaricus reveals a marked drop to 0.78 within the 26 – 30 ℃ window, indicating reduced baseline metabolic cost and greater net energy allocation toward growth and reproduction.

These findings establish 26 -30 ℃ as the narrow thermal optimum for both tropical captive teleost species. Uncoupling occurs at 34 ℃ , where rapid gastric emptying coincides with impaired pepsin catalytic capacity in L. calbasu and elevated respiration costs in L. malabaricus. Aligning feeding schedules with X-ray-derived gastric clearance rates and thermal enzyme thresholds provides a critical bioengineering framework for designing temperature-controlled aquaculture systems, reducing energetic waste, and enhancing climate resilience.