Ontogeny of lymphoid organs and mucosal associated lymphoid tissues in ballan wrasse and the effect of different diets

Ballan wrasse (Labrus bergylta) is used as a cleaner fish in Norwegian aquaculture to control sea lice. Thus, knowledge on the digestive physiology and nutrient requirements, as well as the ontogeny of the immune system is important. In this study, two different diets were tested; diet 1 was used as control diet consisting of artemia and rotifers cultivated and enriched in the in-house facility at IMR, Austevoll, Bergen (Norway). Diet 2 consists in plankton which has successfully been used before in cod larvae generating more robust individuals. Sampling was done according to the standard length of the larvae rather than age (dph). Sampling point 0 (BW0) (4 mm), sampling point 2 (BW2) (4,5 mm), sampling point 3 (BW3) (5,7 to 6 mm), sampling 4 (BW4) (7 to 7,5 mm), sampling point 5 (BW5) (10 to 10,5 mm), sampling point 6 (BW6) (16 to 16,5 mm), and sampling point 7 (BW7) (25 to 30 mm). Ontogeny of lymphoid organs and mucosal associated lymphoid tissues in ballan wrasse and the effect of different diets were investigated. Overall design: Brood stock ballan wrasse (30 females and 6 males) were kept in tanks for a year under optimal conditions before the spawning season (beginning of April 2020). After spawning, eggs were collected and placed in incubators until hatching. At 4 dph, 30 000 to 34 000 individuals were transferred into 6 different tanks (B5 – B10) for the feeding trial were three tanks (B6, B8, and B 10) were fed with control diet (rotifers and artemia) and three tanks (B5, B7, and B9) were fed with plankton (2 diets in experimental triplicates). Formulated feed (dry feed) was given at 40 dph for first time in a co-feeding regime until 56 dph were only dry feed was supplied to all the tanks. A total of 6 sampling points was undergone according to the 6 developmental stages in ballan wrasse. Sampling was done according to the standard length of the larvae rather than age (dph). Sampling point 0 (BW0) (4 mm), sampling point 2 (BW2) (4,5 mm), sampling point 3 (BW3) (5,7 to 6 mm), sampling 4 (BW4) (7 to 7,5 mm), sampling point 5 (BW5) (10 to 10,5 mm), sampling point 6 (BW6) (16 to 16,5 mm), and sampling point 7 (BW7) (25 to 30 mm). At each sampling point a series of pooled larvae were collected from the tank, rinsed with distilled water and immersed in RNA later at 4°C overnight and further kept at -20°C until further extraction.