The ontogeny of New Zealand groper (Polyprion oxygeneios) lymphoid organs and IgM

Abstract

This study investigates the ontogeny of New Zealand groper (Polyprion oxygeneios) immune system, a new species for aquaculture in the Southern Pacific Ocean. In the eggs, both lysozyme and IgM were detected. Egg IgM was found at 1.07–1.56μg/g wet weight and consisted of monomers compared to the polymerized IgM found in adult serum. In larvae, the head–kidney (HK) was first observed at 6dph, followed by the spleen at 16dph, and thymus at 20dph, and within these organs IgM+ cells were first detected in the HK (12dph), then the spleen (32dph) and finally in the thymus and the gastrointestinal tract (45dph). Low levels of Igμ heavy chain transcripts were detected at 2 and 3dph and they increased at 9dph. Igμ expression further increased from day 45 onwards. In juveniles (115dph), the HK and blood showed similar percentages of IgM+ cells as the adult groper. These results highlight the important maturation steps that occur during the development of the immune system in the marine teleost P. oxygeneios.