| In recent years,the potential evolutionary consequences of fishing have received considerable attention.More and more experimental studies have shown that commercial fishing,especially size-selective fishing,may lead to changes in the life history of the exploited species,including the effects on body size,growth and maturity.Changes in phenotypic traits can take place in a relatively short period of time,and have heritable genetic variability.Therefore,this study chose the marine model species-Oryzias melastigma as the target species,set up 90% big-size high-intensity fishing(H-B),90%random-size high-intensity fishing(H-R),75% big-size middle-intensity fishing(M-B),75% random-size middle-intensity fishing(M-R),50% big-size low-intensity fishing(LB),50% random-size low-intensity fishing(L-R)and 75% small-size middle-intensity fishing(M-S),seven different selective fishing strategies.We studied the effects of different selective fishing strategies on the growth and reproduction of F1,F2 and F3 generations,and analyzed the expression of GH-IGF1 growth axis and related genes in different tissues of F2 generation under different selective fishing strategies.The specific results are as follows:(1)Effects of different selective fishing strategies on early survival: Under different selective fishing strategies,egg diameter of O.melastigma was significantly different among different generations(P<0.01),and the egg diameter from F1 to F3 showed an increasing trend.Among different generations with the same fishing strategy,egg diameter of F2 generation was larger than that of F1,among which 90% random fishing strategy had the largest difference,followed by 75% large individual fishing strategy.The egg diameter of the high-intensity fishing strategy group increased the most,and the difference gradually increased from F1 to F3 generation.90% fishing strategy group has a significantly higher hatching rate than other fishing strategy groups,and the 75% and50% fishing strategy groups have relatively small differences between the two generations.Larvae(1-9 days old)have extremely significant differences(P<0.01)between different generations in full length(P<0.01).Under the same fishing strategy,the 75% fishing strategy group has the largest difference among different generations,and the 50% fishing strategy The differences in egg diameter and larvae length were the smallest.(2)Effects of different selective fishing strategies on growth: The growth rate of larvae in the 90% fishing strategy group is slightly lower than that of other fishing strategy groups,and the growth rate of larvae decreases with increasing age,especially in the 90%fishing strategy group,while the growth rate of other fishing strategy groups has relatively little change.The 50% fishing strategy group has a higher growth rate of juvenile fish in different generations in 40-60 days than other fishing strategy groups.With the increase of generations,the limit body length of the 90% fishing strategy group gradually decreases,ranging from 25-26 mm in F1 generation to 18-19 mm in F3 generation;the body length of fishing small individual strategy group gradually increases,and the k value is from F1 generation to The F3 generation gradually increased,and the 50% fishing strategy group had a small difference in the limit body length and k value from the F1 generation to the F3 generation.The F2 generation of the 90% and 75% fishing strategy groups differed greatly in fatness,and the F1 and F3 generations of the 90% fishing strategy group had smaller fatness indexes.The dominant body length group of F1 generation in each fishing strategy group is 20 cm,and the difference between groups is small;F2-F3 generation,the dominant body length group of 90% fishing strategy group has changed from 20 mm to 18-19 mm,showing miniaturization,50% fishing strategy group The dominant body length of the fishing small individual strategy group did not change much in the F2 generation,but in the F3 generation,the dominant body length of the fishing small individual strategy group was 21-22 mm.(3)The impact of different selective fishing strategies on reproduction.The sex ratio of different fishing strategy conditions has also changed significantly.F1 generation,each random fishing strategy group and 75% fishing small individual strategy group have a male-male ratio greater than 1;F2 generation,only 75% random fishing strategy group and 75% fishing small individual strategy.The ratio of male to female in the group is greater than 1.In the F1 generation,the body length,total length and weight of each fishing strategy group were significantly different(P<0.01).Among them,the 90%fishing strategy group and the small individual fishing strategy group were significantly different from other groups(P<0.01);75 % The absolute fecundity and gonadal maturity coefficient of the small individual fishing strategy group are significantly higher than those of other fishing strategy groups.In F2 generation,the body length,total length and weight of the 75% fishing strategy group were significantly different from other strategy groups(P<0.01).The ovarian weight of the 90% fishing strategy group was slightly higher than that of the 75% fishing strategy group and the 50% fishing strategy group.The number of eggs in the small individual strategy group was significantly higher than that of other fishing strategy groups.The fecundity and fatness of the F2 generation were lower than those of the F1 generation,and the small individual fishing strategy group was significantly different from other fishing strategy groups(P>0.05).(4)Expression of GH-IGF1 axis and related genes in different tissues of F2 generation under different selective fishing strategies.In liver tissues,the expression levels of GH,GHR,IGF1 and IGF1-b in the L-B and M-S strategy groups were relatively high,but the expression levels of GHR and IGF1-b in the H-B strategy group were significantly higher than those in other fishing strategy groups;in brain tissue,GH,GHR,IGF1 and IGF1-b are the highest expression levels in the L-B strategy group,and the MS strategy group is second only to the L-B strategy group;in muscle tissue,the four genes have higher expression levels in the L-B strategy group.According to the comparison of morphological measurement data and gene expression levels,H-B,M-B,L-B and M-S strategy groups have significant differences in body length,full length and weight(P<0.05).GH expression level is the highest in the M-S strategy group,and The length of the M-S policy group is also at the maximum.In summary,under the condition of small individual fishing strategy,it can stimulate the secretion of growth hormone of medaka,accelerate growth and increase body length. |
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