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

Abstract

Critical thermal maxima (CTmax), lethal temperature maxima (LTmax), opercular respiration
rate (ORR - movement of operculum per minute), temperature quotient (Q10) and stress
markers of Osteobrama belangeri (Pengba), a high-value medium carp endemic to
hilly ecosystems of North-east India, were examined with the aim of understanding its
aquaculture 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 the
fish significantly increased. Regression analysis indicated a strong positive correlation
between 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 of
CTmax and LTmax and analysed for serum alkaline phosphatase (ALP) activity. The results
indicated 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 suggested
that a water temperature increase above 30°C can impair the physiology of O. belangeri and
consequently, their reproductive competence. Therefore, in such events, proper management
and additional care are necessary to protect them from extinction.

Keywords:
Critical thermal maxima, Lethal temperature
maxima, Osteobrama belangeri, Thermal limit,
Temperature quotient