Can varying photoperiod regimes alter the growth response, behaviour and physiology of Clarias gariepinus?

Abstract

To understand the welfare implication of photoperiod manipulation on Clarias gariepinus, fingerlings (n = 108) and juveniles (n = 108) of C. gariepinus with a mean weight of 3.75±0.03 g and 21.7±2.88 g were exposed to zero light (0L:24D)-T1, average light (12L:12D)-T2 and continuous light (24L:0D)-T3 in triplicates for 35 days. The highest mortality rate was recorded in T2 and T3 for the fingerlings (13.9%) and juveniles (22.2%). T1 recorded a significantly higher (p = 0.03) weekly growth rate and mean weight gain (MWG). Specific Growth Rate (SGR) and Feed Conversion Ratio (FCR) were highest in T1 for both fingerlings and juveniles. Lowest average swimming rate was observed in T1 while the highest aggressive act, bruises, and scars were recorded in T3 for fingerlings and juveniles. The highest (58.6 mg/dl and 56.9 mg/dl) plasma glucose was found in T3 for both fish categories. There were no significant differences (P = 0.11) among the average cortisol levels of both categories of fish at the different photoperiod regimes. Fingerlings and juveniles exposed to 24-hour darkness had a higher MWG, survival rate, SGR and FCR without any physiological stress. A photoperiod regime of 24-hour darkness is recommended for the culture of fingerlings and juveniles of C. gariepinus to boost fish production in the Aquaculture sector.