The effect of prey density, prey size and larval density on the first-feeding response of Southern Bluefin tuna and Yellowtail Kingfish larvae

Southern bluefin tuna are subject to fishery management quotas and consumer demand is rapidly increasing. Aquaculture production could meet this demand. Very high early larval mortalities have slowed successful commercialisation. This study is one component of a larger study which will identify the visual ability of southern bluefin tuna from first-feeding through to metamorphosis using a number of techniques including behavioural experiments, histology and microspectrophotometry. The present study investigated the first-feeding performance of southern bluefin tuna and yellowtail kingfish. Yellowtail kingfish were included in this study to establish if they are a useful surrogate model species having similar oceanic larval stages and rapid growth .We investigated feeding performance in three short-duration (4h) experiments exposing larvae to varying prey size, prey density and larval density regimes. Feeding was assessed by the intensity and the proportion of larvae feeding. Increasing prey density significantly increased the number of southern bluefin tuna feeding and while the incidence of feeding in yellowtail kingfish was much lower, there was no significant response and, an increasing trend was observed. Yellowtail kingfish displayed increasing feeding intensity with increasing larval density unlike southern bluefin tuna which was unaffected by larval densities. The effect of prey size was negligible for both species. Clear similarities between the two species were observed reflecting biological similarities in the small and fast growing oceanic larvae and suggesting methodologies developed for yellow tail kingfish can be adapted to southern blue fin tuna. Nonetheless significant differences were detected suggesting established culture technologies for yellowtail kingfish will need to be modified and tested on southern bluefin tuna and these differences are likely to become greater with ontogeny.