Usingvertebra And Fin Spine Study Age And Growth Of Bigeye Tunain Thewestern Central Indian Ocean

On the basis of722individuals of bigeye tuna (Thunnus obesus) sampledrandomly from longline fishery in the waters of Western Central Indian Ocean fromOctober2012through April2013, this study measured the biological data of bigeyetuna, such as fork length, weight and fat content, etc. Using the corresponding fin spines,vertebrae as materials, the age of bigeye tuna was identified, the relationship betweenage and fork length was analyzed, and the growth equation was obtained.The results indicated that, the fork length range of bigeye tuna was0.57～1.90m,which dominatedin1.11～1.50m, and the individuals were427, accounting for59.3%of the total. The dressed weight range was2～116kg, which dominatedin21～40kg,and the individuals were252, accounting for34.9%of the total. The relationshipbetween fork length and weigh of bigeye tuna was a power function:The fat content of592bigeye tunawas measured.The range was3.1～55.9%, theaverage was13.4%. The dominated fat content was from11.0%to17.0%, accountingfor52.4%.Comparing the fat content in different age groups, the fat content of age oneto three decreased with the increasing age, the highfat content was in the age four to five,the minimum was in the age six, and there was a rising trend from age seven to nine.By analyzing the relationship between the vertebra length, width, andsidediameterand fork length, the power function was the best regression function. Therelationship between vertebraside diameter and fork length was:After staining of the vertebra,394fish’s age were identified.The result showed thatthe age was from two to nine, and the fish of age4～6were accounting for about66.4%.Theelder female samples were lack, and the young samples were lack, too. Based on themethod of Monastyrsky, and the age of the back-calculated fork length, von Bertalaffygrowth equationwas obtained: Using the age derived from vertebrae, the growth equation for the male and femalewas:After analyzing, there was no significant difference between theoretical fork lengthof male or female individuals and that of the combined male and female individuals inthe α=0.05level (PM=0.98, PF=0.48). Theresultsshowed that von Bertalanffy growthequation can describe the growth of male and female. But the PMwas about twice ofPF.The growth equation can describe the growth of male more consistent.We measured548fish’s length(cm) and width(cm) of spine. By regressionanalyzing, the best equation was:The percentage of vascularized area of the dorsal fin spinecross section increasedwith fork length, the average ratio of the vasculature reached62.9%. When identifyingthe age, based on the mean and standard deviation for each ring radius to predictmissing Physalospora position,the mean ring radius and its standard deviation for thefirst radius were1.59mm and0.17mm, respectively; that of the second radius were2.28mm and0.31mm.The best relationship between fork length FL and spine ring radiusr0was:Using von Bertalanffy growth equation, the theory fork length for ageone to eightfish was62.16cm,80.09cm,96.06cm,110.29cm,121.16cm,134.28cm,144.35cm,and153.33cm, respectively. The parameters of growth equation, namely, L,t0,and Kwas226.80,-1.77, and0.12, respectively.Comparing the growth equation which obtained by vertebra and fin spine, therewas quite difference on limit fork length, which was196.99cm and226.80cm,respectively. There was no significant difference (ANCOVA, P=0.72>0.05) betweenthe fork length estimated by the vertebra and fin spine. The fork length estimated by finspine of young bigeye tuna was larger than that of the vertebra.But the fork lengthestimated by the vertebra and fin spine was coincidedincreasing with the age. This study showed that:(1) vertebra and fin spine can be used to study the age andgrowth of bigeye tuna;(2) bigeye tuna male and female are synchronous growth anddevelopment;(3) fat content may change with the corresponding metabolismin thedifferent life history stage, such as growth, reproduction,and aging;(4) age at sexualmaturity of female is3～4years old, and about one year earlier than that of the male,age at sexual maturity of male is4～5years old;(5)thereis differenceamong the bigeyetuna growth equation parameters in different waters.