The Effect of Size-Selective Harvesting on the Growth and Probabilistic Maturation Reaction Norms of Marine Medaka(Oryzias melastigma)

Many commercial fish species show miniaturization, under ageing and early maturation under long-term selective harvesting pressure. In order to investigate the effect of selective harvesting on the growth and probabilistic maturation reaction norms of fish populations, the present study was carried out using experimental ecological methods to design three harvesting strategies, namely, large-harvesting, random-harvesting and small-harvesting, with a harvesting pressure of 50%. After six generations of selective harvesting, the growth and probabilistic maturation reaction norms of the seventh generation of Oryzias melastigma were investigated. The results showed that the maturity of the population of the large-harvesting strategy group was advanced after a long-term of selective harvesting, day-age and length for 50% probability of maturity decreased. The small-harvesting strategy group was opposite. The slope of PMRN in large-harvesting strategy group is positive, and the mature length increased with the increase of age. The slope of PMRN in the groups of random-harvesting strategy and small-harvesting strategy was negative. The mature length decreased with the increase of age. The 55-day-old mature length of the group of small-harvesting strategy was always higher than that of the group of large-harvesting strategy. At the same time, the probabilistic maturation curves of the random-harvesting strategy group were concentrated with smaller differences in the lengths of mature individuals. The probabilistic maturation curves of the small-harvesting strategy group were the most dispersed with larger difference in the lengths of mature individuals. Our findings will provide a reference for the rational development and management of fishery resources.