Genetic ontogeny of pancreatic enzymes in Labrus bergylta larvae and the effect of feed type on enzyme activity and gene regulation
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In the later years increased interest in the use of Labrus bergylta (ballan wrasse) as a cleaner fish on Salmo salar (Atlantic salmon) has caused the emergence of commercial farming of L. bergylta. In order to cultivate such a species, knowledge about its digestive physiology and its nutritional requirements is important, especially in larvae. It has therefore been suggested that a thorough investigation of digestive enzymes related to the pancreas in larvae could be valuable. There were two separate aims of the study. A descriptive part regarding the ontogeny of genes coding for pancreatic enzymes in larvae prior to metamorphosis were performed. Here, the aim was to investigate the effect of age on the relative expression of genes which are related to pancreatic digestion of proteins (trypsin), lipids (Cyp7 A1, BAL, sPLA2 1B) and carbohydrates (amylase, chitinase). Larvae were sampled from the age of 2–55 dph in weekly intervals. In addition to this, an experimental part was performed where the aim was to investigate the effect of different diets on pancreatic enzyme activity in the larvae. We also wanted to investigate the possibility of exogenous enzyme contribution by rotifers (B. plicatilis). Samples of successfully weaned larvae were compared to rotifer fed larvae, including larvae with no gut content. A sample of enriched rotifers was analyzed for comparison. Enzyme activity assays were performed on trypsin, neutral lipase, sPLA2, amylase and chitinase. Our results suggest a consistent feed- dependency in larval L. bergylta at a transcriptional level, where rotifers somehow stimulate upregulation and the formulated feed has the opposite effect. The regulation of BAL was the only exception, where an upregulation was observed as a result of weaning both in the ontogeny series and the experimental part. We did not observe an effect of diet on enzyme activities of neutral lipase, chitinase and sPLA2 in the experimental part. Trypsin and amylase activity assays showed a trend towards a higher activity in rotifer fed larvae, but these values were below the manufacturers LOD (limit of detection).