Functional morphology and feeding behaviour of barramundi Lates calcarifer (Bloch) larvae in intensive aquaculture

High operating costs are identified as a problem with the intensive larval culture of barramundi Lates calcarifer (Bloch). One solution to reduce these costs is to decrease the time the larvae spend in the hatchery being fed live rotifers and brine shrimp nauplii. The overall aim of this study was to describe developmental morphology and feeding behaviour of the larvae under present rearing conditions in order to examine areas where growth and survival can be improved. Larvae displayed diurnal feeding behaviour and consumed prey during daylight hours from day 4 to 10. Prey availability became limited after day 12 with all prey being consumed from the tanks from day 13 onwards. By day 16, all prey were consumed, digested and excreted by larvae within 4 hours after addition of prey to tanks. The ability of larvae to start consuming brine shrimp nauplii was predicted to occur between 2.55 and 4.55 mm TL using measurements of mouth gape and prey size. Larvae actually began consuming brine shrimp nauplii at 3.28 mm TL. The majority of larvae began to consume brine shrimp nauplii between 3.99 and 4.33 mm TL. Larvae reared under continuous lighting had the best growth rates during the rotifer feeding stage (day 2 - 10). However, larvae reared in 16 hour light and 8 hour dark had the best growth rates for the brine shrimp feeding stage (day 8 - 20). Survival was not significantly different (P>0.05) between treatments during the rotifer feeding stage but was higher for larvae reared in 8 hour light and 16 hour dark from day 8 - 20. Larvae reared in the black containers grew more quickly than larvae reared in white and transparent containers for the rotifer feeding stage (days 2 - 10). However, tank colouration had no effect on growth or survival of larvae for the brine shrimp feeding stage (days 8 - 20). Brine shrimp nauplii availability levels to obtain maximum growth and survival of larvae was investigated between days 8 - 23. Brine shrimp nauplii availability levels increased from 120 individuals/larva/feed from day 8 - 15 to 750 individuals/larva/feed from day 15 - 20. This research showed that the rearing conditions presently used for barramundi larvae can be modified to substantially improve growth and survival. Recommended changes to photoperiod and tank colour would reduce the rotifer feeding stage by 4 days, representing a significant reduction in overall production costs.