Severe mortality in common sole (Solea solea) at post-weaning stage following environmental stress

Common sole (Solea solea) is one of the most interesting species for diversification of aquaculture production in the Mediterranean area, but production of sole on an industrial scale has not yet begun. In the present study, larval rearing was performed in 1 cubic meter tanks with a re-circulating system, using the “green water” technique. Aer an initial mortality occurred during the first 10 days of larval rearing, no particular mortality was registered during weaning period until 69 dph (day post hatching). On 66 dph, because of technical problems, fish were transferred in a new tank with open system where temperature control was not possible and water temperature increased from 19°C to 24 °C in three days. Four days later and for the following ten days we registered a mortality rate of 84.5%. Microbiological analysis revealed the absence of Betanodavirus and the presence of Vibrio anguillarum O2 and of Tenacibaculum maritimum; the former represents the first isolation on common sole in Italy. Histology revealed necrotic-haemorrhagic lesions in brain, kidney and gut, and severe skin erosions, the laer especially on fish collected at the end of the outbreak. Moreover the pathogens have been detected by immunohistochemistry (IHC). This severe mortality could be interpreted as a multi-factorial event where post-weaning weakness, manipulation, higher temperature and pathogens could have had a synergic effect. The extreme stress susceptibility of S. solea, pointed out in this and previous papers is discussed.