Health status evaluation of striped bass (Morone saxatilis) exposed to low temperature in sea cage culture during the grow‐out

Striped bass (Morone saxatilis) is a species with high production potential for human consumption. However, like any other cultured species, they are prone to be exposed to adverse climate conditions, compromising their health status until a certain degree compromises the success of reaching commercial size. It is proposed that haematological parameters testing during the whole growing out season represents a useful tool to assess the overall fish health status. Information on M. saxatilis haematology is limited. Therefore, the present study aimed was to provide the haematological and blood chemistry values for commercial striped bass grow‐out. Fish from three different group sizes and under low sub‐optimal temperature (16 to 18°C) were sampled in correlation to copepods (Peniculus sp.) present attached to the fins. Thirty fish from each group (sized 0.17, 0.54 and 1.17 kg, corresponding to different ages and batches) were all sampled (blood and external parasites count) during the spring (5 June, June 12 and June 16, 2019). The results show that differences in blood parameters were only observed according to the weight of striped bass such as the haematocrit (HCT), haemoglobin, mean corpuscular haemoglobin concentration (MCHC), white blood cells (WBC) count, total protein, globulin, ratio A/G, cholesterol, triglycerides and glucose. In contrast, the copepods present showed a preference for the caudal fin of the striped bass, followed by the first dorsal and pectoral fin. The smaller fish (0.179 kg) were the most susceptible to Peniculus sp., compared to the largest fish (1.174 kg). So far, it can be concluded that at this stage, the copepod does not show any adverse effect on the fish health since the condition factor and blood parameters were statistically similar along with the different copepod infestation levels (intensity ranged from 7 to 109). However, this new copepod, here registered for the first time in the Morone saxatilis, was registered during the sunset to increase environmental temperature. Even if no signs of a harmful relationship between parasites between young and old organisms, it will be necessary to be further monitored. The copepod incidence and the blood parameters should be analysed along the year (different temperatures), aiming to detect any correlation to the copepods present or, in any case, the overall health status or another parasite present under the seabass culture conditions.