Mortality reduction in yellowtail kingfish (Seriola lalandi) larval rearing by optimising Artemia feeding regimes

Mortality is a major concern in larval fish rearing during exogenous feeding. An important cause of mortality of larval yellowtail kingfish (Seriola lalandi) during the rotifer - Artemia weaning period was hypothesised as being due to larval sinking response after satiated feeding prior to dusk. This paper documents the effect of larval body density change under different Artemia feeding regimes and adds to the understanding of the cause of mortality of yellowtail kingfish larvae. The change in body density was used as a tool to determine the time of last feed in a day to ensure larvae were neutrally buoyant at dusk. An adaptive Artemia feeding regime was implemented, in which the amount of feed applied to the larvae was modified based on the body density. Larvae were denser than the seawater in which they were reared when fully satiated with Artemia. The time required to return to pre-feeding density significantly decreased with larval age. At 12days post hatch (dph), the peak in body density of larvae fed Artemia to satiation was 1.0320gcm -3 and they did not return to a pre-feeding body density (1.0260gcm -3), for approximately 10h. By 19dph, larval body density only increased to 1.0275gcm -3 when larvae were fully satiated and they were neutrally buoyant again by 4h. The decrease in larval body density when fully satiated at 16dph demonstrated that overfeeding larvae with Artemia should be avoided prior to dusk before this age to maintain neutral buoyancy. The use of the adaptive regime reduced mortality by 20% compared with the control, from 13 to 17dph, without sacrificing larval growth. Transition to Artemia feeding is a critical stage for yellowtail kingfish larvae and mortalities can be significantly reduced during this period by managing the timing of Artemia feeds throughout the day. The strategy of an adaptive feeding method may be considered a novel management tool to prevent larval sinking and associated mortality during the period of weaning from rotifers to Artemia during larval rearing.