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

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 1.07–1.56 μg/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 6 dph, followed by the spleen at 16 dph, and thymus at 20 dph, and within these organs IgM+ cells were first detected in the HK (12 dph), then the spleen (32 dph) and finally in the thymus and the gastrointestinal tract (45 dph). Low levels of Igμ heavy chain transcripts were detected at 2 and 3 dph and they increased at 9 dph. Igμ expression further increased from day 45 onwards. In juveniles (115 dph), 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.

► Groper eggs contain lysozyme and IgM. Egg IgM is a monomer compared to the polymerized serum forms.
► Groper immune organ development follows the classic pattern described in other marine fish.
► IgM+ cells first populated the HK (12 dph), then the spleen, thymus and GI tract.
► Igμ heavy chain expression began at 9 and 115 dph juveniles had similar HK and blood IgM+ cells than adults.