Study On Biological Characteristics,sagittal Otolith Morphology And Microchemistry Of Trichiurus Lepturus In The Gulf Of Oman

Trichiurus lepturus is one of the main catches in bottom trawling in the Gulf of Oman and one of the main fishing targets in China’s trans-oceanic fishery.Therefore,the study of hairtail in this sea area and the supplement of biological data of hairtail in this sea area can provide data reference for further study of population structure,resource development and utilization and spatial distribution of hairtail in this sea area.Based on the biological data and sagittal otolith samples collected during fishing exploration in the Gulf of Oman from June to August 2017 and May to September 2018,the biological characteristics and sagittal otolith morphology of Trichiurus haumela in the Gulf of Oman were preliminarily studied.The population composition of Trichiurus haumela in the Gulf of Oman,morphological characteristics of sagittal otolith of Trichiurus haumela,growth pattern of sagittal otolith and determination of trace elements in sagittal otolith of Trichiurus haumela were analyzed.The main results show that:(1)1560 samples were measured from July to August 2017.The anal length ranged from 110 mm to 552 mm(SD = 58.74,SE=1.49),with an average anal length of 241.01mm;1051 samples were tested from May to July 2018.The anal length ranged from 125 mm to 580 mm(SD = 66.59,SE= 2.05),with an average anal length of 233.7 mm ANOVA analysis showed that there was a significant difference in anal length distribution between 2017 and 2018(F= 8.71,p = 0.003 < 0.01)(2)894 female samples and 666 male samples were tested in 2017.ANOVA analysis showed that there were significant differences in the distribution of female and male fork lengths in 2017(F=9.37,p = 0.006 < 0.01);618 female samples and 433 male samples were tested in 2018.ANOVA analysis showed that there was a significant difference in the distribution of female and male fork length in 2018(F=11.03,P=0.0009<0.01)(3)The weight range of 1560 samples measured in 2017 is 10.3-1756.1g(SD=169.05,SE=4.28),and the average weight is 201.72 g;The 1051 tail weight measured in 2018 ranged from 15.5 g to 1909.2 g(SD = SD = 204.61,SE=6.31),with an average weight of 201.90 g g.According to ANOVA analysis,there was no significant difference in weight distribution between 2017 and 2018(F=0.0006,p = 0.98 > 0.05).(4)The ratio of male to female measured in 2017 is 1.34(SD=0.04,SE = 0.03);The ratio of male to female measured in 2018 is 1.43(SD=0.11,SE=0.06).The ratio of male to female measured in 2018 is 1.43(SD=0.11,SE=0.06).ANOVA analysis showed that there was no significant difference in the distribution of sex ratio between 2017 and 2018(F=1.25,P=0.34>0.05)(5)The proportion of gonadal maturity II and III is the largest in 2017,accounting for 40.7% and 25.8% respectively.Gonadal maturity in 2018 is also mainly distributed in phases II and III,with percentages of 55.4% and 20.5% respectively.Compared with 2017,the proportion of phases II and IV increased in 2018,but decreased in phases I,III and V.(6)Power function regression analysis results of anal length and body weight of 1560 samples measured in 2017:Overall: relationship between anus length and body weight:W = 2.2322× 10-5L2.8967(R 2= 0.9695,n=1560)Female: relationship between anal length and body weight:W = 2.7854× 10-5L2.8544(R 2 = 0.9777,n=894)Male individual: relationship between anal length and body weight:W = 2.3725× 10-5L2.8852(R 2 = 0.9559,n=666)Power function regression analysis results of anal length and body weight of 1051 samples measured in 2018 are as follows:Overall: relationship between anus length and body weight:W = 2.1282× 10-5L2.8965(R 2 = 0.9074,n=1051)Female: relationship between anal length and body weight:W = 2.4131× 10-5L2.8817(R 2 = 0.9785,n=618)Male individual: relationship between anal length and body weight:W = 1.8544× 10-5L2.9319(R2 = 0.9515,n=433)(7)The variance analysis was used to compare the difference between age and anal length and between age and body weight between 2017 and 2018.The results showed that there was no significant difference in the age of the samples measured between the two years(p=0).Therefore,Von Bertalanffy growth equation analysis was carried out for the samples measured in the two years.The expression is:The results show that the theoretical maximum anal length of hairtail in the Gulf of Oman is 957.32 mm and the theoretical maximum body weight is 3596.76 g g.The anal length and body weight of hairtail in the Gulf of Oman have been increasing with age,the growth rate of anal length has been decreasing with age,and the growth rate of body weight has been increasing with age.It can be clearly seen from the figure that the acceleration of body weight increase shows a decreasing trend.(8)Observation shows that the sagittal otolith of hairtail in the Gulf of Oman can be divided into four main parts: Anterior,Posterior,Dorsal and Ventral.The overall bending is long fusiform,the surface is uneven and uneven,there are obvious main interstices,the reverse side of the main interstices has obvious ridgelike uplift,the back side is thicker than the ventral side,the base leaf is longer than the wing leaf and is more prominent than the wing leaf.Principal component analysis was carried out on 20 morphological parameters of hairtail in the Gulf of Oman.The results showed that the contribution rates of the first,second and third factors to explain morphological parameters were 71.963%,13.725% and 5.575% respectively,with a cumulative of 91.263%.According to the factor load factor,Determining the total length of sagittal otolith(TST),the height of sagittal otolith(TSH),the length from the center of sagittal otolith to the front end(DCR),the length from sagittal otolith basal leaf to the moment orifice(DRI),the length from sagittal otolith basal leaf(TRL)and the length from sagittal otolith wing leaf to moment orifice(DAI)can represent 20 morphological parameters to describe the morphological characteristics of hairtail sagittal otolith.TST,TSH and DCR describe the changes of sagittal otolith as a whole,DRI,TRL and DAI describe the changes of sagittal otolith basal lobe and pterygoid lobe.(9)By analyzing the relationship between the main morphological parameters of the sagittal ear and the size of the fish body such as the sagittal otolith area(OA)and otolith weight(OW),it is shown that the growth of otolith continues the whole growth process of hairtail in Iranian waters.The results show that the growth pattern of each part of the sagittal otolith shows allometric growth: the long axis and short axis of the sagittal otolith all grow allometric with time.On this basis,the growth rate of the front and back of the otolith is greater than that of the back and ventral of the otolith.The base blade and the wing blade also become more and more obvious with the increase of time.The increasing speed of the wing blade is greater than that of the base blade,and the outward protrusion of the wing blade becomes more and more obvious.At the same time,under the condition that there is no significant difference in the increase rate of OA with the growth of fish body,the relative difference in the increase of OW results in more and more obvious concaveconvex flat characteristics on the sagittal otolith surface.(10)A total of 47 trace elements were detected in all otolith samples by laser ablation inductively coupled plasma mass spectrometry.Except Ca,there are 9 kinds of major trace elements,namely Na,Sr,Fe,Mg,Ba,Li,Zn,Mn and Cr.In different age stages of Trichiurus lepturus otolith,there are significant differences in Na,Fe,Sr,Mg,Li,but no significant differences in Ba,Zn,Cr,Mn.In different age stages,there is no significant difference in Ba/Ca(p = 0.55 > 0.05),Mg/Ca(p = 0.28 > 0.05),Mn/Ca(p = 0.070 > 0.05),Sr/Ca(p = 0.86 > 0.05).