Assessment of Osteobrama belangeri (Pengba), a high-value medium carp endemic to North-east India for thermal tolerance limits

Critical thermal maxima (CTmax), lethal temperature maxima (LTmax), opercular respirationrate (ORR - movement of operculum per minute), temperature quotient (Q10) and stressmarkers of Osteobrama belangeri (Pengba), a high-value medium carp endemic tohilly ecosystems of North-east India, were examined with the aim of understanding itsaquaculture potential and management requirements in the event of a temperature rise.Fish (7.82±0.35 cm/4.64±0.36 g) were acclimatised at 20, 25 and 30°C in insulated tanks(10 fish per tank) for 30 days. They were then exposed to a water temperature increase(@ 1°C day-1) using a locally-fabricated thermostat and assessed for CTmax, LTmax and ORR.As the acclimation temperature increased from 20 to 30°C, CTmax, LTmax and ORR of thefish significantly increased. Regression analysis indicated a strong positive correlationbetween acclimation temperatures and CTmax (y = 0.22x + 33.55, R² = 0.97) and LTmax(y = 0.27x + 32.86, R² = 0.99). Fish blood samples were collected at the endpoints ofCTmax and LTmax and analysed for serum alkaline phosphatase (ALP) activity. The resultsindicated that the fish experienced maximum stress at an acclimation temperature of 30°C(ALP: 38.7 U l-1), followed by 25°C (35.6 U l-1) and 20°C (31.7 U l-1). The results suggestedthat a water temperature increase above 30°C can impair the physiology of O. belangeri andconsequently, their reproductive competence. Therefore, in such events, proper managementand additional care are necessary to protect them from extinction. Keywords:Critical thermal maxima, Lethal temperaturemaxima, Osteobrama belangeri, Thermal limit,Temperature quotient