Roe enhancement in sea urchin: Effects of handling during harvest and transport on mortality and gonad growth in Strongylocentrotus droebachiensis

Sammendrag

This study addresses effects of handling and air exposure during harvest and transport on mortality and gonad growth of Strongylocentrotus droebachiensis in a proceeding roe enhancement trial. Two experimental factors: (1) handling (gentle and rough) and (2) degree of air exposure (wet and dry) were combined to form 4 different treatments; gentle/dry (GD), rough/dry (RD), gentle/wet (GW) and rough/wet (RW). In the proceeding roe enhancement trial, the highest mortality, exceeding 25%, was observed in the GD treatment. Mortality was 1.5% in RW and RD treatments, whereas no mortality was observed in the GW treatment. Mortality only occurred during the first 4 weeks after harvest. Desiccation appears to be the main cause of mortality. There was a significant increase in gonad index for all treatments during the roe enhancement trial; from 7.6% (median) at the beginning of the trial to 15.7, 14.5, 13.5 and 11.2% (median) at the end for GW, RW, GD and RD respectively. However, the increase in gonad index was significantly lower in the RD compared with the others. The lower gonad growth in RD was probably caused by the high frequency of individuals with visual injuries, a frequency that was an order of magnitude higher than in the other treatments. Overall, there was a clear relationship between visual injuries and gonad index, where individuals with injuries had a significantly lower gonad index at the end of the experiment (median; 10.4%) compared individuals without visual injuries (median; 14.5%). The lower feed consumption and higher feed conversion factor observed in RD indicate that individuals with injuries have a reduced gonad growth caused by a combination of reduced appetite and lower feed conversion efficiency. Regeneration of spines and lesions may have resulted in less resources allocated to gonad growth.