Preliminary Study On Heterosis Of Hybrid Yellow Catfish "Huangyou 1"

As an important aquaculture species in China,Pelteobagrus fulvidraco is popular among consumers due to their excellent meat quality and high commercial value.In recent years,due to environmental changes,overfishing and other factors,the individual miniaturization of yellow catfish has intensified,and the germplasm resources have declined seriously.On the other hand,the inbreeding caused by the expansion of the yellow catfish seedling breeding industry has resulted in the low quality of the fish,the weakening of disease resistance,and which have caused huge economic losses to farmers.Therefore,the emergence of new varieties is urgently needed in the yellow catfish breeding industry.The utilization of hybrid advantages has become one of the important ways to improve fish production and improve fish quality,and has been applied in production,showing good application prospects.The hybrid yellow catfish“Huangyou-1”was obtained from third generation of female P.fulvidraco and the second generation of male P.vachelli.Our study first explored the optimal breeding temperature and density.Secondly,the hybridization advantages of hybrid yellow catfish"Huangyou-1"were initially analyzed,including the comparison of growth situation,nutritional analysis,genetic diversity and disease resistance,which provided reference data for understanding the excellent traits of hybrid yellow catfish"Huangyou-1".The main results are shown as follows:1. Comparison of growth performance of hybrid yellow catfish"Huangyou-1"and its parentsFirstly,the optimal breeding temperature and density of hybrid yellow catfish"Huangyou-1"were explored by indoor circulating aquaculture system.The results showed that when the water temperature was higher than 39?,the mortality of the fry exceeded 75%.Meanwhile,the fish entered a state of torpor and hardly ingested food when the water temperature was lower than 11?.In the range of 14?35?,the weight gain rate and specific growth rate of hybrid yellow catfish“Huangyou-1”increased first and then decreased at each breeding temperature;the final weight and day weight gain and specific growth rate decreased significantly with increasing aquaculture density.By regression fitting analysis,the maximum growth rate of the fish was 28.95?;the stocking density was 1.927 kg/m³ to achieve maximum productivity.Next,the growth comparison of hybrid yellow catfish"Huangyou-1"and its parents was investigated,after 90 days of homogenization.The results showed that the hybrid yellow catfish"Huangyou-1"had the highest final body length and final body weight,the daily weight gain rate and daily growth rate of the hybrid catfish"Huangyou-1"were significantly higher than that of the female P.fulvidraco,and there was no significant difference of the daily growth rate between male P.vachelli and hybrid catfish"Huangyou-1".By calculation,H_MP of body length and body weight of hybrid yellow catfish"Huangyou-1"was 10.67%and 29.16%,respectively;the H_BP was 4.37%and 18.13%,respectively.The hybrid yellow catfish"Huangyou-1"showed obvious growth heterosis.2. Comparison of nutrient content of hybrid yellow catfish"Huangyou-1"and its parentsThe nutrient components of the muscle of the hybrid catfish"Huangyou-1"was measured and compared with the parents.The results showed that the moisture content was 76.90%,the crude protein was 18.40%,and the crude fat and crude ash content was 3.70%and 1.10%,respectively.Furthermore,the crude protein content was higher than its parental P.fulvidraco?15.37%?and P.vachelli?17.15%?.The hybrid catfish"Huangyou-1"contained 17 kinds of amino acids,the amino acid content was 16.16%,the essential amino acids were 6.9%,the umami amino acids were 6.14%,and the essential amino acid index was 72.18.The ratio of essential amino acids to the total amount of amino acids was as follows:hybrid catfish"Huangyou-1"?42.70%?>P.fulvidraco?41.37%?>P.vachelli?39.42%?,indicating hybrid yellow catfish"Huangyou-1"belongs to high quality nutrition.3. Comparison of genetic diversity of hybrid yellow catfish"Huangyou-1"and its parentsIn this study,we developed 40 microsatellite markers for P.vachelli from expressed sequence tag sequences.After 32 out of 40 markers were effectively amplified in P.fulvidraco and the hybrid yellow catfish"Huangyou-1".The genetic diversity and genetic relationship of the hybrid yellow catfish"Huangyou-1"and their parents were analyzed.The results showed that the hybrid catfish"Huangyou-1"showed a relatively high genetic diversity when compared with their parents,with an average allele number of 5.75,the largest observed heterozygosity?0.62?,and the largest PIC?0.59?.The genetic distance of the hybrid catfish"Huangyou-1"and P.vachelli?1.23?was higher than that of the hybrid catfish"Huangyou-1"and P.fulvidraco?1.20?,lower than the genetic distance from P.fulvidraco to P.vachelli?1.68?.UPGMA cluster analysis indicated that the hybrid catfish"Huangyou-1"inherited more genetic information from female parent.4. Comparison of disease resistance of hybrid yellow catfish"Huangyou-1"and its parentsThe hybrid catfish"Huangyou-1"and the parental offspring of juveniles"Huangyou-1"and its parents'disease resistance,including the survival rate,immune-related enzyme activity and gene expression were compared and analyzed after challenged with A.hydrophila or E.ictaluri.Results showed that hybrid population possess higher survival rate than P.fulvidraco,and no significant difference with P.vachelli after A.hydrophila injection.The hybrid population showed higher survival rate than parental populations after E.ictaluri injection.The activity of each immune-related enzyme activity in the liver tissues of three kinds of fish was basically the same,and both showed a trend of increasing first and then decreasing.The hybrid catfish"Huangyou-1"processed higher fold change ofSOD,CAT,GSH-P_X,ACP,AKP and LZM than its parental populations after challenged with A.hydrophila;the expression levels of AKP,GSH-P_X and Cu/ZnSOD at m RNA and the expression levels of Cu/ZnSOD and MnSOD at protein were higher than those of the parents,and the others were only higher than P.fulvidraco.The hybrid catfish"Huangyou-1"showed higher fold change ofSOD,CAT,GSH-P_Xand LZM compared with that of the parents after challenge with E.ictaluri.The fold change of ACP and AKP was higher than that of P.fulvidraco,and there was no significant difference with P.vachelli.The expression levels of AKP,LZM,GSH-P_Xand Cu/ZnSOD at m RNA and Cu/ZnSOD and MnSOD at protein levels were higher in the liver than in the parents,and the others were not significantly different from P.vachelli.The comprehensive satisfaction rate of hybrid yellow catfish"Huangyou-1"was calculated,result showed the H_MP was 43.54%,and the H_BP was 24.21%,indicating that the hybrid yellow catfish"Huangyou-1"was superior to the parents in comprehensive disease resistance,especially the female parent.