Effect of different photoperiods on the growth and physiology of rohu (labeo rohita)

Abstract

The Cunent study was aimed to investigate the effect of diverse photoperiods on the growth performance, physiological indices and general morphology of indigenous fish . ?' species Rohu(Labeo rohita}. Three hundred healthy fingerlings of L. rohita having ~,,, ". average initial body weight 6.95 ± 0.53 g were stocked in 12 glass aquaria, well ';, equipped water heater, aerators and overhead fluorescent tube lights, at a stocking density of 4gL-1 (22-23 fish! aquarium).Completely randomize experiment was designed consisting of four groups PI, P2, P3 and P4 exposed to four different photoperiod 6L118D, lOLl14D 14L110D, 18L16D respectively for 90 days. During experimental duration, all water quality parameters i.e., temperature (26.5±0.5°C), total ammonia «0.25 mg L- 1 ) , and DO (6.0 ± 0.8 mg L-1 ) , levels were kept at optimum level while requisite photoperiods were maintained by fluorescent light tubes instalied 13cm above the surface of the aquaria. At the completion of study, PI group of fish showed significant (P<0.05) increase in the growth performance as compared to other experimental groups. Similarly, Feed conversion efficiency was comparatively higher in PI group of fish reared under long day photoperiod. Manipulation of photoperiod also affects the circadian pattern and concentration of cortisol. Fish of PI group exposed to 18L: 6D, showed a circadian-like pattern, highest levels of water-borne cOliisol during· 18-24 hIS with peak at 20:00 hr. A shift of peak level from 20 to 24hrs was observed in others groups exposed to different photoperiods. However, the maximum cortisol level was in a group of fish exposed to 18 hI prolonged scotophase. Similarly, significantly high glucose level was detected in the P4 group of fish exposed to prolong dark exposure compared to PI exposed to continuous 181u' light duration. Similarly, complete blood count (CBC) indicated significantly higher (P< 0.05) values of HB (g dL-') MCV (fL), MCH (pg), L YM%, RBCs (l0\tL-1 ) and MCHC (%) in a Plgroup and Hct (%) in a P4 group of fish as compared to other groups. However, WBCs did not show any significant difference (P>0.05) among all experimental groups. Prolong scotophase also caused darker body colorations, deep yellowish spots on the body, damaging of skin and scales as well as narrowing the body structure. The results of this study indicate the negative' impact of prolong scotophase and suggest long day photoperiod for gaining more production per unit area of this species.