Effects of photoperiod manipulation (24L:0D) on somatic growth and endocrine responses in juvenile Barramundi (Lates Calcarifer)(Bloch)

Photoperiod manipulation is a widely used technique in commercial aquaculture to influence endogenous rhythms in fish, which enables industry to control events such as reproductive timing, maturation and growth. The ability to use photoperiod manipulation to influence these events has benefited commercial industry by improving production of fish, thereby generating increased economic benefits. The majority of photoperiod manipulation research has being applied to temperate species, whereas recently these techniques have also been successful in sub-tropical and tropical species. Photoperiod manipulation research on barramundi has demonstrated conflicting results, and clarification is required as to whether using extended day length is effective in enhancing growth of juvenile barramundi. This thesis confirms photoperiod manipulation to be effective at enhancing growth of juvenile barramundi. In the majority of experiments, continuous light (24L:0D) significantly increased wet weight, total length and SGR weight and length of juvenile barramundi when compared to rearing fish under 12L:12D. In addition, growth increases observed in fish reared under 24L:0D occurred without significant increases in feed intake, demonstrating higher feed conversion efficiencies compared to fish reared under 12L:12D. As the Australian barramundi industry currently only uses photoperiod manipulation to manipulate spawning events, this research enables commercial farmers to use this technique to improve growth as well. To confirm photoperiod manipulation techniques were applicable and effective in commercial conditions, a commercial scale experiment was undertaken, with juvenile barramundi demonstrating significant increases in growth when reared under 24L:0D supplied by artificial lighting.