Dynamics of sexual development in teleosts with a note on Mugil cephalus

The process of sex determination(SD)and sex differentiation(Sd)with associated sex-specific behaviour in teleosts is brought about by genetic factors and environmental factors under the influence of chemical messengers.SD is initiated by inherited genes,which in turn influence Sd by the production of hormones.To understand the plasticity of SD in fishes,the functional role of genes must be clearly elucidated.During early development,the dimorphic expression of male and female are mediated by the differentially sexualized brain.In mammals,SD region(SDR)on the Y chromosome(SRY)can be considered as male-specific copy of SOX3 and in the absence of SRY in teleosts suggests SD might be regulated by alternate genes.DM(doublesex/mab)-related genes,AMH(anti-mullerian hormone),TGF-b(transforming growth factor beta),GSDF(gonadal soma derived growth factor)and other genes(around 18)located in chromosomes of teleosts are found to be responsible for SD.The SD gene,sdY(sexually dimorphic on the Y chromosome)has been detected in more than 15 salmonid species,and in medaka and tilapia SD system is governed by heterogametic mechanism.In mullet,Mugil cephalus Dor et al.identified 27 SDR genes and suggested to be potential candidate genes for SD.Recently whole-genome sequencing data were produced from mullet and assembled into a draft genome sequence in which>30 loci are potentially associated with SD.Further analysis is required to know the involvement of each sex-biased gene for its functional influence on sex.Investigators attempted to know the sex-linkage group in tilapia and found that 2 linkage group i.e.LG1 and LG22 show SD loci,whereas in mullet it was documented that LG8 is the SD loci.Rigorous study with all male population(YY)or knockout of male marker gene,might give conclusive understanding on SD in future.The review highlights the absence of genomic understanding of SD and SDR genes for futuristic direction of research.

Heavy metal levels in the liver and muscle tissues of the four commercial fishes from Lake Balik,Kızılırmak Delta(Samsun,Turkey)

Objective:To determine the levels of some heavy metals in the liver and edible tissues of four fish species[Mugil cephalus L.,1758(M.cephalus),Cyprinus carpio L.,1758(C.carpio),Perca fluviatilis L.,1758(P.fluviatilis)and Stizostedion lucioperca L.,1758(S.lucioperca)]collected from Lake Balik,Kizilirmak Delta(Samsun)for analysis of Cu,Co,Pb,Zn,Cd,Mn,Ni and Fe.These metals were chosen because at higher concentrations there might be toxic to the fish and by extension humans that depends on such fish as food.Methods:The concentrations of the metals were carried out by the flame atomic absorption spectrophotometer(UNICAM 929).Results:Large differences in heavy metal levels were observed between liver and muscle tissues within each fish.The results showed that the Fe concentrations were the highest and Cd concentrations were the lowest in livers and edible tissues of the four species.The muscles of C.carpio accumulated significant higher levels of Co,Zn and Ni than other species.Cu was higher in the muscles of S.lucioperca than those in other species,while M.cephalus showed more of Mn and Fe levels.The muscles of P.fluviatilis accumulated significant higher levels of Pb and Cd than other species.However,the liver of M.cephalus accumulated significant higher levels of Co,Mn and Fe than other species.The level of Cd was the highest in the liver of P.fluviatilis,while S.lucioperca showed more of Cu and Pb,and the higher levels of Zn and Ni was measured in the liver of C.carpio.Conclusions:The metal levels obtained were compared with the maximum permitted levels in food of the Turkish Food Codex and Commission Regulation(EC).The results of this study showed that estimated daily and weekly intakes of selected metals via consumption of fish were below the permissible tolerable daily intake and provisional tolerable weekly intake values established by Food and Agriculture Organization/World Health Organization.