Increased water temperature interrupts embryonic and larval development of Indian major carp rohu Labeo rohita

Temperature is among the critical determinants of the physiology of fishes and other heterotherms throughout the life history. Temperatures outside of the optimal range distress embryonic and larval development with untoward consequences later in life. To understand the effect of high temperature on embryogenesis and organogenesis, the commercially important rohu carp (Labeo rohita) was chosen. Rohu embryos and larvae were reared at four different temperatures (30, 32, 34, and 36 degrees C), and indices of their hatching, development, and mortality were observed throughout early development. Embryos exposed to 30 and 32 degrees C showed normal development with highest rates of hatching success. Embryos at 34 degrees C displayed evidence of damaged zygotes, cellular deformities, damaged yolk sac coupled with shortest incubation time, and the lowest rates of hatching success. No hatching was observed at 36 degrees C, and these embryos displayed coagulated organs, dark yolk sac, irregular segmentation, and pustules. Larvae of rohu exposed to 34 and 36 degrees C showed developmental deformities (fusion in the eye, axial curvature, yolk sac ulceration, blood coagulation, tail shortening, and ulceration) and minimal survival. Our results suggest that optimal temperature of rohu embryo and larvae is 30-32 degrees C or lower; higher temperatures disrupt embryonic metabolism and physiology, resulting in aberrant and unsuccessful early development.