| The newly hatched larvae needs to uptake quantity of energy to meet the needs of development and the skeleton related to survival are preferentially developed.Skeletal development is important in fish fry breeding because of its influence on external morphology and functional exercise.Skeletal development in larval fish originates with the formation of cartilage.Skeletal deformity usually occurs in many cultured fishes and results in movement difficulty,growth retardation,even extremely high mortality,and leading to significant finical lose and labor force waste.Scophthalmus maximus（L.1758）belongs to the order Pleuronectiformes,family Scophthalmidae,and category Scophthalmus,and it was suitable to inhabit in cold water and was natural distribution in the coast of Northeastern Atlantic.Epinephelus lanceolatus belongs to the order Perciformes,family Serranidae,and category Epinephelus,and mainly distributed in the Southeast Asia and Australia waters,the islands of South China Sea and Hainan Island.S.maximus and E.lanceolatus are important mariculture species in China with high growth rates and economic values.However,the incidence of skeletal deformities are ubiquitous,particularly the E.lanceolatus,the incidence of abnormalities could up to 96%.In the present study,we systematically investigated the growth characteristics,timing and progression of skeletal development,types and incidence of skeletal deformities during the breeding process of S.maximus and E.lanceolatus.The results are as follows:1.Growth characteristics,timing and process of skeletal development,types and incidence of deformity in larva and juvenile S.maximus.The cultivating temperature of newly hatched larvae maintained at 16±0.5°C until 4 days post hatching（dph）.The temperature was maintained at 21°C from 5 dph to 24 dph and then the temperature was maintained at 23±0.5°C until to the end of the experiment.The culture conditions were as follows:greenwater,dissolved oxygen 7.0–8.5 mg L–1,salinity 30–32,pH 7.7–8.0,and constant aeration were provided.After hatching,the larvae were fed with Brachionus plicatilis from 4 dph to 19 dph,then the larvae were fed with Artemia sp.nauplii from 13 dph to 35 dph,and compounded diet was fed from 25 dph.The total length of larva increased slowly during the pre-metamorphosis stage,during the metamorphosis and post-metamorphosis stages,the juvenile enter into a rapid growth period.During the pre-and early-metamorphosis stage,the development of cranium presented as positive allometric growth,while the vertebral column was negative allometric.These results shows that skeleton related to food ingestion and respiration were preferentially developed.In climax-and late-metamorphosis period,cranium was negative allometric,and the vertebral column was nearly isometric growth.The cranium and vertebral were both nearly isometric growth when the juvenile enter into the late-metamorphosis stage.The cranium elements relevant to food ingestion and inspiration developed preferentially,such as the Michael’s cartilage,hyoid bar,hypohyal and ceratobranchial.The cranium skeletal elements were basically formed before the larva enter into early-metamorphosis stage,then the jaw,dentary and opercle ossified preferentially.Asymmetries gradually presented in some elements of cranium,for example,the sympletic and hyomandibular on the right side became shorter or smaller than the one on the left,the dentary,ectopterygoid and quadrated became wider or longer than the one on the left.And the eye on the right side moved to the left side.Vertebral elements were not observed until the formation of haemal and neural arches in the midriff and anterodorsal regions,respectively.Subsequently,it formed backwards and the ossification of spinal following a similarly pattern.Only the pectoral fin was observed before first feeding,followed by the caudal fin,dorsal fin,anal fin and pelvic fin,however,the pectoral fin was the last fully developed fin.8.15%incidence of deformities were observed during the the breeding process,uncoordinated appearance possed the hightest incidence 4.5%,followed by spinal deformities,its incidence was 2.3%and primarily presented as vertebra fusion,scoliosis,lordosis,and kyphosis,the incidence of cranium deformities was 0.5%and mainly included jaw and operculum deformities,and fin deformities occurred at the lowest incidence 0.85%and mainly included caudal fin,dorsal and anal fins deformities.Spinal and cranium deformities could significantly affected the external morphology and growth.BMP4,Sox9 and Gpc4 participate in a wide range of biological processes,and expressions of them maintain at a certain level in different tissues of adult fish.BMP4,Sox9 and Gpc4 had a higher expression level at the early development stage and gradually decreased,this pattern of gene expression corresponding to their founctions during the process of development.2.Growth characteristics,timing and process of skeletal development and types and incidence of deformity in larva and juvenile E.lanceolatus.The cultivating conditions were as follows:greenwater,the temperature maintained at 29±0.5°C,dissolved oxygen 7.0–8.5 mg L–1,salinity 30–32,pH 7.7–8.0,weak laser and constant aeration were provided.After hatching,from 2 dph to 10 dph the larvae were fed with S rotifers,from 6 dph to 27 dph the larvae were fed with L rotifers,from 16 dph to 40 dph the larvae were fed with Artemia sp.nauplii,and from30 dph to 45 dph the larvae were fed with Artemia sp.The total length of larva increased slowly during the pre-and early-metamorphosis stage,and the juvenile enter into a rapid growth period during the late-and post-metamorphosis stages.During the pre-and early-metamorphosis stage the development of cranium and caudal fin presented as positive allometric,while the vertebral column was negative allometric.In late-and post-metamorphosis period,the cranium,vertebral column and caudal fin complex were nearly isometric growth.Cranium elements relevant to food ingestion and inspiration were preferentially developed,such as the Michael’s cartilage,hyoid bar,hypohyal and ceratobranchial.After the cranium elements fully formed,some skeletal elements undergone a degradation processes,such as hyosympletic,hyoid bar,palatoquadrate and ceratobranchial.The ossification of cranium initiated during late-metamorphosis period,and the maxillary,premaxillary,dentary and opercle were ossified preferentially.The vertebral elements development initiated with the formation of neural arch at the anterior of the spinal,then the neural arch at the center part of spinal was formed accompanied with the formation of haemal arch in the midriff regions,and the haemal arch was formed forwards and backwards.Only the pectoral fin was observed before first feeding,followed by dorsal and pelvic fin.The dorsal and pelvic spine appeared at the time enter into early-metamorphosis stage,it lengthened rapidly and undergone a degenerative process.96%incidence of deformities were observed during the breeding process of E.lanceolatus.The cranium deformities possessed the highest incidence 82%and primarily including jaw and branchial deformities.Followed by vertebral column deformities 12%and mainly including loidosis,kyphosis,scoliosis and vertebra fusion.The fin deformity had the lowest incidence 2%.Cranium and vertebral column anomalies could significantly affected the external morphology and growth,and even high mortality during the pre-and early-metamorphosis stage.In addition,a significant cannibalism were observed in about 20%-30%bigger individuals during the first fry separation,and it maybe another reason leading to lower survival rate during post-metamorphosis stage. |
PDF Full Text Request