First feed matters: The first diet of larval fish programmes growth, survival, and metabolism of larval ballan wrasse (Labrus bergylta)

The use of cleaner fish, such as the ballan wrasse (Labrus bergylta), is important for combatting the sea lice problem in salmonid cage farming. Ballan wrasse is the only wrasse species that is cultivated, though only about 50% of the approx. 3 million ballan wrasse used in 2020 was produced by aquaculture. The major obstacle for large scale cultivation of ballan wrasse is the difficult first feeding phase and a lack of functional feeding protocols. Like most pelagic marine fish larvae, ballan wrasse do not accept inert diets as first feed, and feeding regimes based on rotifers and Artemia (brine shrimps) usually lead to mixed results and are far from being optimal nutrition for the larvae. In a 48-day start feeding experiment, we studied the feasibility of replacing rotifers by an Experimental cirriped diet or copepod nauplii (Acartia tonsa) and replacing Artemia by nauplii of the cirriped Semibalanus balanoides. Later, all treatments received the same formulated diets. We sampled larvae at each feed transition to analyze different response variables such as growth, morphometry, gene expression, lipidomics, histology, and microbiology. We found significant differences in survival rates and growth. Larvae fed copepods as the first diet had significantly higher survival rates than larvae start-fed on either rotifers or small experimental cirripeds, and this pattern was also reflected in early growth and bone development. Gut histology at the end of the experiment (48 days after hatching) showed a more developed intestinal tissue in the larval group fed copepods first and cirripeds as the second diet compared to the other larval groups. Gene expression at day 48 post hatch still revealed pronounced differences between the larval group first fed on rotifers and larvae from the other three feeding regimes which received natural, unenriched diets. Even weeks after receiving the same formulated diets, lipidomics analyses revealed that several lipid species correlated either negatively or positively with larval growth rates or mortality. Our results are a clear indication for nutritional programming, pointing towards the importance the first diet has for the further life of a fish.publishedVersio

Can lipidomics help identifying egg quality in ballan wrasse?

Ballan wrasse (Labrus bergylta) is in the limelight of aquaculture research due to the species role as cleaner fish in salmon aquaculture. A major drawback is that the salmon industry still depends on wild caught fish as there are still many unsolved challenges in ballan wrasse aquaculture, amongst them the determination of egg quality. We measured a range of different egg quality markers on 6 different batches of eggs from ballan wrasse. Additionally, we performed lipidomics on these eggs to test whether their lipid profiles relate to, and can be thereby used as, a predictor for egg quality. We identified relationships between several lipid species and physiological and morphological egg quality markers, and the lipids grouped into two groups. The first group consisted of a diverse blend of 32 lipids, and was positively correlated with size related measures while it was negatively related to measures describing metabolic activity. It consisted of phosphatidylcholines (PC), lysophosphatidylcholine (lysoPC), and triacylglicerids (TAG) and three different sphingomyelins (SM). The second group consisted of 24 lipid species, and showed the inverse pattern, positive relationships with metabolic activity and negative relationships to size related measures. This group of lipid species contained several phosphatidylethanolamines (PE) and free fatty acids. These lipid species may be proposed as key egg quality markers which ultimately can be used by the aquaculture industry to select high quality egg batches in hatcheries.publishedVersio