Study On The Fishery Biology Of Hexagrammos Agrammus And Hexagrammos Otakii In Lidao Rongcheng

The two greenling species, Hexagrammos agrammus and Hexagrammos otakii,belong to Scorpaeniformes Hexagrammidae Hexagrammos, and are distributedthroughout Northwestern Pacific Ocean, from Japan to the Korean Peninsula, andfrom East China Sea, Yellow Sea to Bohai Sea. The two species are dominantyear-around demersal fish in Lidao Rongcheng and inhabiting rocky reefs or algalareas of shallow coastal waters. Fishery biology of H. agrammus and H. otakii wereinvestigated based on818individuals and499individuals respectively, which werecollected monthly from the shore reef of Lidao Rongcheng between March2010andMarch2011. The main results were as follows:(A) Study on the fishery biology of H. agrammus(1) Age and growth of H. agrammus: The standard length (L) ranged58~236mm and body weight (W) ranged3.2~251.0g. There was no significant differencebetween the females and males in both standard length and body weight distributions.The dominant range of standard length was100~160mm, while the dominant rangeof body weight was3.2~75.0g. Relationship between standard length and bodyweight was W=1.0×10-5L3.1022(R2=0.9640).Sagittal otoliths of H. agrammus were small and thin, and the ring marks wereclear after otoliths had been grinded. Marginal Increment Analyses (MIA) showedthat the annual rings were formed from April to June. Using otolith weight to confirmthe ring marks was reliable, since there was no significant difference between otolithweight distributions and age distributions. The age for females and males ranged both0+~4+year old and the dominant range of age was0+~1+year old. The minimum ageof females and males at the first reproduction were both0+year old, and the minimumstandard length and body weight were measured to be110mm and30.1g for females,and91mm and16.6g for males, respectively. The von Bertalanffy growth equations were Lt=241.4[1e-0.34(t+0.64)] andWt=246.4[1e-0.34(t+0.64)]3.1022. The growth rate was fastest in0+~1+year old, andthen it became slow. The Fulton’s condition factor (K) indicated that the growth ratewas gradually increased in spring, and became fastest in summer, but graduallydecreased in autumn, and became slowest in winter.(2) Reproductive biology of H. agrammus: The sex ratio was1.71:1, andfemales obviously outnumbered males. Gonads were classified into6phases: I~VI.Macroscopic criteria were based on the colours, sizes of ovaries and sizes of eggs forfemales, as well as the colours and sizes of testes and whether the sperm ducts werefilled with milt for males. Different sizes of developing eggs in phase III~V wererecognized by the naked eye. The purple-dark ripe eggs, which were coexisted withgelatinous adhesive material, migrated to the post-ventrally sides of ovaries to beready for spawning in phase V. Histological sections of ovaries showed that differentstages of oocytes in phase II~VI were found at the same time, especially pre-matureoocytes coexisted with empty follicles.Monthly changes of the maturity phases, GSI and HSI determined the spawningseason annually extending from late October to middle January (the watertemperature was5~17°C), and the main spawning period was October and November.The65specimens belonging to the standard length classes from110~203mm andbody weight classes from30.1~152.5g, carried an average number of981±302eggs.Fecundity was significantly correlated with standard length and body weight. The eggdiameter distributions of phase IV~V were0.7~2.2mm, which consisted of threediscontinuous groups. Consequently, H. agrammus appeared to be a multiple spawner.(3) Feeding ecology of H. agrammus: H. agrammus was the demersal-feedingfish. Among the11prey groups, polychaeta was the dominant prey group, and otherprey groups included fish eggs, algae, seagrass, stomatopoda, amphipoda and fish, etc.The dietary composition had obvious seasonal variations: besides polychaeta was theimportant prey group in every season, stomatopoda and decapoda in spring, fish andcrabs in summer, fish eggs and fish in autumn, and fish eggs were mostly in winter.The dietary composition also had obvious ontogenetic variations:<80mm SL preyed on seagrass and algae;80~199mm SL preyed on polychaeta, fish, decapoda andcrabs;>199mm SL preyed on fish, polychaeta and fish eggs. The feeding intensityhad obvious seasonal variations, with highest in summer and lowest in winter. Thefeeding intensity also had obvious ontogenetic variations, reached the highest feedingintensity in <100mm SL, then decreased with increasing standard length, andgradually increased after>180mm SL.The seasonal range of Shannon’s diversity index (H’) for dietary compositionwere1.58~1.91, and Pielou’s evenness index (J’) were0.69~0.86, therefore the dietaryniche breadth was widest in autumn and narrowest in summer. Five samples could beidentified based on DNA barcoding, among which, four samples were identified asspecies, and one sample was identified as genus.(B) Study on the fishery biology of H. otakii(1) Age and growth of H. otakii: The standard length (L) ranged57~245mmand body weight (W) ranged3.0~266.1g. There was no significant differencebetween the females and males in both standard length and body weight distributions.The dominant range of standard length was90~150mm, while the dominant range ofbody weight was3.0~50.0g. Relationship between standard length and body weightwas W=7.0×10-6L3.1832(R2=0.9883).Sagittal otoliths of H. otakii were small and thin, and the ring marks were clearafter otoliths had been grinded. Marginal Increment Analyses (MIA) showed that theannual rings were formed from March to May. Using otolith weight to confirm thering marks was reliable, since there was no significant difference between otolithweight distributions and age distributions. The age for females and males ranged both0+~2+year old and the dominant range of age was0+~1+year old. The minimum ageof females and males at the first reproduction were both1+year old, and the minimumstandard length and body weight were measured to be125mm and30.7g for females,and116mm and25.2g for males, respectively.The von Bertalanffy growth equations were Lt=250.5[1e-0.43(t+0.31)] andWt=302.7[1e-0.43(t+0.31)]3.1832. The growth rate was fastest in0+~2+year old. TheFulton’s condition factor (K) indicated that the growth rate was gradually increased in spring, and became fastest in summer, but gradually decreased in autumn, and becameslowest in winter.(2) Reproductive biology of H. otakii: The sex ratio was1.39:1, and femalesobviously outnumbered males. Gonads were classified into6phases: I~VI.Macroscopic criteria were based on the colours, sizes of ovaries and sizes of eggs forfemales, as well as the colours and sizes of testes and whether the sperm ducts werefilled with milt for males. Different sizes of developing eggs in phase III~V wererecognized by the naked eye. The yellow-gray ripe eggs, which were coexisted withgelatinous adhesive material, migrated to the post-ventrally sides of ovaries to beready for spawning in phase V. Histological sections of ovaries showed that differentstages of oocytes in phase II~VI were found at the same time, especially pre-matureoocytes coexisted with empty follicles.Monthly changes of the maturity phases, GSI and HSI determined the spawningseason annually extending from middle October to middle December (the watertemperature was7~19°C), and the main spawning period was October and November.The60specimens belonging to the standard length classes from125~227mm andbody weight classes from30.7~186.7g, carried an average number of2544±846eggs.Fecundity was significantly correlated with standard length and body weight. The eggdiameter distributions of phase IV~V were0.9~2.4mm, which consisted of threediscontinuous groups. Consequently, H. otakii appeared to be a multiple spawner.(3) Feeding ecology of H. otakii: H. otakii was the demersal-feeding fish.Among the10prey groups, fish was the dominant prey group, and other prey groupsincluded polychaeta, decapoda, algae, crabs and stomatopoda, etc. The dietarycomposition had obvious seasonal variations: besides decapoda was the importantprey group in every season, crabs and polychaeta in spring, fish in summer, fish weremostly in autumn, and polychaeta were mostly in winter. The dietary composition alsohad obvious ontogenetic variations:<80mm SL preyed on decapoda and amphipoda;80~119mm SL preyed on polychaeta, stomatopoda larvae and decapoda;>119mm SLpreyed on fish, decapoda and crabs. The feeding intensity had obvious seasonalvariations, with highest in summer and lowest in winter. The feeding intensity also had obvious ontogenetic variations, reached the highest feeding intensity in <80mmSL, then decreased with increasing standard length, and gradually increasedafter>180mm SL.The seasonal range of Shannon’s diversity index (H’) for dietary compositionwere1.40~1.72, and Pielou’s evenness index (J’) were0.78~0.89, therefore the dietaryniche breadth was widest in autumn and narrowest in spring. Six samples could beidentified based on DNA barcoding, among which, four samples were identified asspecies, and other two samples were identified as genus and family respectively. Thesimplified Morisita’s index showed that there was an intense food competitionbetween H. agrammus and H.otakii in summer and autumn, and the main competitiveprey groups were fish and polychaeta.