Studies Of Molecular Responses Of Lined Seahorses,Hippocampus Erectus,to Essential Foods And Environmental Factors

Seahorse(Hippocampus spp.)is a small marine bony fish.The aquarium market and the Chinese herbal medicine market have great demand for seahorses and have considerable potential economic value.However,overfishing and habitat destruction have caused a sharp decline of seahorse resource worldwide in recent years.Rearing of seahorses in captivity has become a palliative activity to curb unsustainable seahorse trade.Food and water environments are key factors affecting its survival and reproductive ability in seahorse aquaculture.At present,the coastal areas of China have formed two main types of seahorse breeding models with obvious differences between north and south due to differences in geographical environment and natural resources.Seahorses in North China were commonly fed Artemia in indoor containers with a stable water environment,while most seahorses in South China were fed copepods in outdoor concrete ponds.Although outdoor farming can greatly save costs,the unstable water environment leads to low survival rate of seahorses.These two breeding models have caused major differences in the efficiency of seahorse breeding in the north and south of China.Seahorse are extremely sensitive to the environment,and the water used for breeding is mostly inshore seawater.In recent years,coastal waters have been seriously polluted,and highdose endocrine disruptors(EDCs)have been reported in the water environment.Studying the response mechanism of seahorses to endocrine disruptors can help reduce the potential harm of pollution to seahorse breeding.Based on the current hot issues in the field of international seahorse breeding,combining the characteristics of actual seahorse breeding in China,this paper innovatively discusses the study of the differences between southern and northern seahorse breeding models and their impact on seahorse breeding efficiency.This study promotes the development of the seahorse aquaculture industry in China,and provides important scientific data for the systematic analysis of the environmental adaptation mechanism of seahorse and other offshore biological resources.This research paper takes the lined seahorse(H.erectus)as the research object,reasearching and comparing the two main seahorse breeding models in northern and southern China.Firstly,we compared the effect of two main seahorse diets(Artemia in the north and copepods in the south)on the growth and physiology of juvenile seahorses based on a 30-d feeding experiment.Second,the potential effects of salinity(15 and 30 ppt)and ammonianitrogen(0,5,and 15 mg/L)on juvenile seahorse physiological stress were studied through a 5-d orthogonal experiment.Finally,through a 60-day experiment with Flutamide,an EDCs,on sexually mature male seahorse,the response characteristics and potential molecular mechanisms of the seahorse brood pouch and testis to EDCs were systematically revealed.The main research progress obtained is as follows:1.Feeding Artemia and copepods had no effect on seahorse body length.However,the insulin-like growth factor 1(igf-1)gene expression was significantly higher in the liver of seahorses fed copepods than in the lever of seahorses fed Artemia,suggesting that copepods promoted better growth.Lower leptin gene expression in the liver of seahorses fed Artemia than in those fed copepods proved that Artemia was better for satiating the juveniles.A high expression of stress-related genes,namely,heat shock proteins 70(hsp70)and Mn superoxide dismutase(Mn-sod),in the liver of the seahorses that were fed copepods suggested that copepods might cause more stress on juveniles.2.Both lower salinity and higher ammonia-nitrogen increased the ventilation rate of seahorse significantly.Significant changes in the m RNA expression of genes,including Na+: K+:2Cl-cotransporter 1(nkcc1)and Na,K-ATPase(nka)in the gill,hsp70,Mn-sod,glutamate dehydrogenase(gdh),and glutamyl synthase(gs)in the liver,indicated that seahorses are sensitive to acute salinity decline.In addition,high ammonia-nitrogen exposure significantly changed the expression of genes(i.e.,Mn-sod,gdh,and gs)in seahorses exposed to low salinity level,while no significant variation was observed in seahorses exposed to normal salinity,suggesting that salinity decline might increase the negative effects of ammonia-nitrogen stress.3.Flutamide causes malformation of the seahorse’s testis and causes atrophy of the brood pouch.In addition,the seahorse’s androgen level rise in the hippocampus rises and hormonerelated genes are affected.Analysis of the transcriptome results shows that Flutamide mainly affects steroid hormone biosynthesis,retinol metabolism,apoptosis and other pathways,as well as affecting regulation of organ growth,regulation of p H and positive regulation of immune system process,leading to the function of brood pouch is impaired and interferes with spermatogenesis and development-related pathways and affects biological functions such as striated muscle cell differentiation.,suggesting that flutamide reduces the fertility of seahorses.In summary,this study expounded the effects of main diets and environmental factors of lined seahorse on its growth and reproduction from the perspective of behavior,physiology and molecular level,and explored the molecular regulation characteristics of endocrine disruptors on the development of seahorse brood pouch and testis based on transcriptome data.