Water temperature induced interannual variation in spawning of Japanese Spanish mackerel Scomberomorus niphonius in the northern Yellow Sea

Japanese Spanish mackerel Scomberomorus niphonius is a pelagic,neritic species that occurs in the Yellow Sea in high commercial value.The spawning period of this fast-growing species is controlled by water temperature.Based on microstructural analysis of otoliths from 145 young-of-the-year(YoY)S.niphonius collected by trawl in 2017,2018,and 2020,and the temporal variation in the spawning period in the northern Yellow Sea,and its relationship to water temperature were examined.We found that the spawning lasted from late April to late June but differed in year:in 2017 it occurred from April 23 to June 1 and peaked in early May,in 2018 it extended later from May 7 to June 29,and in 2020 from May 6 to June 22 and peaked later from late May to mid-June.The highest temperature in 2017 corresponds with the earliest end of the spawning period and a lower growing degree-day(GDD,℃·day)of 383℃·day.In 2018,slower warming corresponds with a longer spawning period,and a GDD spawning period of 506℃·day.Rapid warming in late 2020 corresponds with a spawning peak,and a GDD spawning temperature of 448℃·day.Despite differences in spawning period,the water temperature when spawning commenced was 10-12℃.Therefore,water temperature is the major determinant of the spawning period,affecting both the starting and the ending of spawning.This study improved our understanding of the spawning dynamics and environmental adaptation of S.niphonius,and how these might change in environments subject to increased warming.

Reproductive characteristics of Psilorhynchus homaloptera Hora and Mukerji,1935 (Cyprinidae: Psilorhynchidae) in the lower Yarlung Zangbo River,Tibet

Psilorhynchus homaloptera mainly inhabits turbulent waters in the lower reach of the Yarlung Zangbo River,Tibet,China,and it is the only species of Psilorhynchus in China.However,many important aspects of its biology remain poorly documented,which hinders the conservation eff orts.Therefore,we studied its reproduction using 801 specimens from the Motuo sector of the lower Yarlung Zangbo River from December 2015 to November 2016.The sex ratio was 0.68꞉1(male꞉female)for the overall population.Females reached a larger total length and weight(134 mm and 18.6 g)than males did(113 mm and 12.2 g).Lengths at maturity were estimated 80.0 mm for males and 93.1 mm for females.Our analyses of gonad development and the size distribution of oocytes suggest that P.homaloptera is a single spawner with the peak spawning period between September and October.Furthermore,the estimated mean absolute fecundity was 557±204 eggs per fish,and mean relative fecundity was 50.9±10.9 eggs per g of female weight.The fecundity of P.homaloptera increased linearly with increasing total length,total weight,ovary weight,and age.This study on the reproductive biology of P.homaloptera demonstrates that the fish was in a vulnerable state due to the increasing anthropogenic activities in the lower Yarlung Zangbo River.

Age,growth and reproduction of Sarcocheilichthys nigripinnis from the Qingyi Stream in the Huangshan Mountains

Identifying the life-history strategies of fish and their associations with the surrounding environment is the basic foundation in the conservation and sustainable utilization of fish species.We examined the age,growth,and reproduction of Sarcocheilichthys nigripinnis using 352 specimens collected monthly from May 2009 to April 2010 in the Qingyi Stream.We found the sex ratio of this study population was 0.58:1(female:male),significantly different from expected 1:1.Females and males both comprised four age groups.The annuli on the scales were formed during February and March.No obvious between-sex difference was observed in length-weight and length-scale-radius relationships.The total length in back-calculation significantly increased with age for both sexes,but did not differ significantly at each age between the two sexes.An inflection point was observed in the growth curves given by the von Bertalanffy growth function for total weight.At this inflection point,fish were 3.95 years.Both sexes reach their 50%sex maturity at age 2,when females and males were 94.7 mm and 103.0 mm total length.The temporal pattern of the gonado-somatic index corresponded to a spawning period that occurred from April through July.The non-synchronicity of egg diameter in each mature ovary during the breeding period suggested these fish may be batch spawners.The absolute fecundity increased significantly with total length and weight,whereas no significant correlation was observed between the relative fecundity and body size.

Reproductive biology of largehead hairtail(Trichiurus lepturus)in south-eastern Australia

Knowledge of reproductive biology and life-history traits of populations exploited by fisheries is important for their sustainable management.We investigated the life-history traits of Trichiurus lepturus(largehead hairtail)in south-eastern Australia;a region of low exploitation for this otherwise heavily exploited circumglobal species,to investigate whether there were differences in the reproductive biology and life-history traits in the south-east Australian population compared with those in other regions.We also used histological sections to examine male and female gonads at a microscopic level.Trichiurus lepturus in south-eastern Australia had a greater maximum length(193 cm total length(TL)),matured at a larger length(108 cm TL at 50%mature)and had a spawning period(March to September,Austral winter)that was inconsistent with other regions.The overall sex ratio of 1:0.4 females:males was consistent with a female dominant sex ratio observed in other regions,particularly in larger length classes.However,females in the current study dominated samples from both estuarine and coastal habitats,as well as during the spawning and non-spawning periods,which is not consistent with the patterns found in other regions.Differences in south-eastern Australia may relate to limited fishing pressure,genetic variation,or differences in environmental factors that influence reproductive development,including temperature,trophic resources and habitat.

Reproductive aspects of the coastal trevally,Carangoides coeruleopinnatus in Terengganu Waters,Malaysia

This study describes for the first time the reproductive biology of the coastal trevally(Carangoides coeruleopinnatus)(Ruppel,1830)caught from Terengganu waters,Malaysia.Monthly sample collection from April 2019 to March 2020 was done at Pulau Kambing fish landing port in Terengganu,Malaysia.A total of 687 individuals comprise of 362 males(52.69%)ranged from 6.3 cm to 26.6 cm(mean±SD:13.2±3.84 cm)and 325 females(47.31%)ranged from 9.0 cm to 26.4 cm(mean±SD:13.9±3.34 cm)were observed.The sex ratio significantly deviated in favor of males(1:0.90)(χ^(2)=1.99).However,there are significant differences between sexes over months in June(χ^(2)=10.89),July(χ^(2)=11.91),August(χ^(2)=6.10)and September(χ^(2)=4.41).The monthly variation of the gonadosomatic index(IG)peaked between February and April for males and females,indicating its spawning period.The interpretation between condition factor(K)and hepatosomatic index(IH)showed that the energy mobilization from the body assists the gonad maturation.The batch fecundity of 42 mature females ranged from 15.7 cm to 21.4 cm,and mass was 142.6 g-333.0 g giving 20,438 to 121,829 eggs.The length at first maturity of males and females were 12.45 cm and 15.78 cm,respectively.The male reached earlier maturity than the female.This study increases the understanding of reproductive aspects of C.coeruleopinnatus for future formulation of rules and regulations for suitable fishery management in Terengganu waters.