| Micropterus salmoides,commonly known as "California bass",belong to Perciformes,Percoidei,and Micropterus.They originated in the freshwater bodies of the Americas and were introduced in Guangdong Province in 1983.The breeding output has continued to expand because of its delicious meat,short breeding cycle,strong adaptability,and easy fishing.In 2020,the national breeding output reached 478,000 tons,and the farming area was about 18,700hm2.It has become an important freshwater economic fish in China.In this study,the traditional morphological detection method was used to collect the proportional traits data of head length,body length,tail peduncle length,body height,and body width of 122 male and female M.salmoides individuals.Then,sex molecular markers were used to identify the sex of juvenile M.salmoides,where the growth curves of male and female M.salmoides were plotted.Finally,sex-specific molecular markers of M.salmoides were screened based on resequencing technology.The main research contents are as follows.1.Comparison of male and female shapes of M.salmoidesIn this study,122 male and female M.salmoides samples were collected,and 13 measurable proportions of male and female M.salmoides were measured for 13 traits of total length,body length,snout length,head length,tail peduncle length,and body height by traditional morphological measurements:detection and analysis.The one-way ANOVA results showed no significant differences in the 13 groups of morphological variables between females and males of M.salmoides.The discriminant function of male and female M.salmoides was established using the stepwise discriminant analysis method,and the results showed that the overall accuracy of the discriminant function was 61.5%.The results of the principal component analysis demonstrated that the first main component dominates the traits related to the head and tail axis of the fish body.The second principal component is for the characteristics of the dorsal and ventral axis of the fish body.The third component plays a key role in the relationship between traits and fish body movement.The cumulative contribution rate of the three principal components is 58.589%.This study shows there is no significant difference in external morphology between male and female M.salmoides,and the difficulty in identifying the sex of M.salmoides by external morphology,which a more accurate identification method needs to be found.2.Development of sex-specific molecular markers for M.salmoidesTen males and ten females of M.ides were selected for resequencing at a depth of 10X.Using SOAPnuke to process the raw data of the selected samples,the average Clean Reads per individual is 68,170,069bp,and the average Clean Bases of each individual is 10,225,510,350bp.The quality value Q20 ranges from 94.10%to 95.57%,with an average of 94.82%.The proportion of bases G and C(GC Content(%))ranges from 41.62%to 42.37%,with an average of 42.03%.Comparing the filtered genome with the published M.salmoides genome,the single nucleotide polymorphisms and insertion/deletion sites used for primer design can be obtained,including 289 SNP differential sites and 36 In/Del differential sites.The sex-specific molecular markers of M.salmoides were screened according to the InDel differential sites.The marker was validated by PCR using 36 male and 36 female fish of known gender,and the results show that all males had one band,and none of the females had a band.This study provides support for rapid identification of the genetic sex of M.salmoides,control of sex ratios in breeding populations,and selection of breeding parents.3.Comparison of growth performance of male and female M.salmoidesIn this study,M.salmoides samples of different ages were collected,the gender of the samples was identified by the sex-specific molecular markers screened,and the morphological data of female and male fish were recorded,respectively.One-way analysis of variance was performed on the body weight and body length of male and female M.salmoides.The experimental result shows that at 120 days of age,the average body weight of male fish was 36.82±12.93g,and the average body weight of female fish was 30.55±9.03g,where the difference is extremely significant(p<0.01).The body lengths of male and female fish were 11.64±1.28cm and 11.12±1.13cm,respectively,where the difference is significant(p<0.05).At 270 days of age,the average body weight of male fish was 438.42±48.85g,and the average body weight of female fish was 415.69±59.59g,with a significant difference(p<0.05).According to the experimental result,the absolute weight gain rate of male and female M.salmoides showed an increasing trend,where the rate of male fish was slightly higher than that of female fish during the same period.The absolute growth rate of the body length of male and female M.salmoides first increased,rising continuously from 0 to 180 days and then decreased from 180 to 270 days.From 0 to 120 d,the absolute growth rate of the male M.salmoides was higher than that of the female fish,from 120 to 180 d,the absolute growth rate of the female fish exceeded that of the male fish,and from 180 to 270 d,the absolute growth rate of the female fish body length was higher than that of the male fish.The plumpness of male and female fish first decreased and then increased,and there was no significant difference during the whole period.The body weight and body length of male and female M.salmoides were fitted using power functions W=0.0248L2.9884(R2=0.9939)and W=0.0218L3.0374(R2=0.9947).The growth equations of male and female M.salmoides are all close to 1,and the fitting degree is high.The plumpness of male fish attained the maximum at 180 days of age,which is 2.5489±0.2175g/cm3.The amount of accumulated weight of Male and female M.salmoides increased first,then decreased,where the weight of female fish attained the maximum at 180 days of age,which is 0.2752(g·cm)/d.At the age of 180 days,the body length of the female fish gradually became larger than that of the male fish.At the age of 180-270 days,the absolute growth rate of the female fish was higher than that of the male fish,which was consistent with the results of the growing volume and plumpness of the male and female M.salmoides.To sum up,for M salmoides that have been reared within one year,the growth performance of male fish is higher than that of female fish. |
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