Startfeeding of ballan wrasse (Labrus bergylta) larvae using different feeding regimes (NTNU)

There is an increasing demand for cleaner fish by the salmon industry to combat the sea lice problem. To reduce the use of wild caught ballan wrasse there is an ongoing effort to produce ballan wrasse in captivity. To date there are no standard procedures, and e.g. mortality rates vary from hatchery to hatchery and also between years. Ballan wrasse larvae are tiny and not very developed when they hatch. Their first feed has to be live feeds, as larvae of this species cannot digest pelleted feeds. The current 'industry standard' feed used to rear larvae in Norway are rotifers at the onset of external nutrition, followed by a transition to artemia nauplii, before the fish can be weaned on dry diets. Both, rotifers and artemia are known to be feeds of inferior food quality, which often results in high mortality rates, low growth rates and low disease resistance of larval fish (Hamre et al., 2013; Nielsen et al., 2017; Øie et al., 2017), and the use of these feed items is solely owed to the ease of accessibility and application. To reduce mortality and deformation in larval rearing of ballan wrasse we aim at developing feeding regimes using natural plankton (larval stages of copepods and barnacles) which are known to be of superior compared to rotifers and artemia. These have only recently become commercially available and are hence underutilized at present. The experiments will be conducted in flow through systems in 200 L tanks in triplicates. We will test 3 novel, size adaptive feeding regimes against a 'state of the art' industrial feeding regime. Larvae will be analysed for growth, prey selectivity, biochemical composition, as well as gene expression. The experimet includes 120 000 larval ballan wrasse from start-feeding. We do not expect that the fish will suffer more during the experiment than under normal production strategies.