Effects of different photoperiods on growth performance and health status of largemouth bass (Micropterus salmoides) juveniles

Abstract

This study investigated the effects of photoperiod duration on growth, heamatological and blood biochemical parameters, and antioxidant capacity of largemouth bass (Micropterus salmoides). Triplicate groups of juvenile fish (33.22 ± 4.68 g) were kept in a recirculating aquaculture system and exposed to five different photoperiods [light/dark (L/D), h] as follows: 8L:16D; 12L:12D; 16L:8D; 20L:4D and 24L:0D. All the fish were fed a commercial diet at a fixed ratio of 1% body mass with daily inspection of the consumed feed. The experiment lasted 16 weeks and fish growth was monitored at 4-week intervals. The results revealed the significant effect of photoperiod duration on growth rate and feed utilization. The constant light exposure (24L:0D) benefited weight gain (WG) only during the first four weeks while thereafter negative impacts were noticed. At the end of the feeding trial, the highest WG and specific growth rate were obtained in the 8L:16D group which significantly differed from those of the 12L:12D and 16L:8D groups. Although fish feed intake was not influenced by photoperiod duration, better feed conversion ratio was found in the 8L:16D group. Moreover, the same group exhibited the highest hepatosomatic and gonadosomatic indices, and haemoglobin concentration. The highest plasma total protein and globulin concentrations were recorded for the 16L:8D group. Plasma glucose concentration decreased by prolongation of light duration while opposite trends were observed for plasma ammonia concentration and creatinine kinase activity. The highest alanine aminotransferase and aspartate aminotransferase activities were found in 20L:4D and 12L:12D groups, respectively. Moreover, plasma alkaline phosphatase activity significantly decreased in 12L:12D and 16L:8D groups. Longer light duration led to remarkable increase of thiobarbituric acid reactive substances (TBARS) concentration in fish liver, brain and gill indicating the incidence of oxidative stress. Likewise, boosted antioxidant responses were found in liver [glutathione (GSH) and glutathione S-transferase (GST)], brain (GST) and kidney (superoxide dismutase) as light duration extended. These findings suggest that 8 L:16D is favouring better growth, organosomatic index and antioxidant capacity of largemouth bass juveniles reared in RAS.