Year‐round natural spawning,early development,and the effects of temperature,salinity and prey density on captive ornate goby Istigobius ornatus (Rüppell, 1830) larval survival

Natural spawning, early development and larviculture of the ornate goby Istigobius ornatus in captivity were studied for the first time. I. ornatus spawned 46 times from 31 October 2013 to 31 October 2014. Fecundity ranged from 246 to 10,214 eggs per clutch, with an average hatching rate of 77.8% ± 9.9% (M ± SEM). Fertilized eggs (1.31–1.54 × 0.46–0.50 mm in diameter) were adhesive demersal and oval‐shaped. Embryonic development lasted 84 hr at 27.5 ± 0.5°C. Newly hatched larvae [2.12 ± 0.04 mm in total length (TL)] transformed to the juvenile stage completely when TL was 7.79 mm. Effects of different water temperatures (24, 28 and 32°C) and salinities (10, 15, 20, 25, 30, 35 and 40 g/L) on per cent survivals (%) and survival activity indices (SAIs) were tested. Survival was not significantly different under different temperatures; SAIs was significantly higher at 28°C. Larvae showed the significantly higher survival and SAIs at salinities 10–30 g/L than at 35 and 40 g/L. Effect of different prey densities on survival was significantly higher in 7 days post hatch larvae fed 20 and 30 rotifers/ml. These findings could guide future programs in captive breeding technology development and commercial production of other marine ornamental gobies.     

赣江下游丰城江段鱼类早期资源现状调查

对赣江鱼类早期资源的调查,可为赣江鱼类资源保护以及水利工程生态调度提供科学依据.2017年5-7月,在赣江丰城段使用圆锥网采集鱼卵和弶网采集仔鱼,对鱼类早期资源种类组成、产卵规模和产卵场进行分析.结果显示,调查期间共采集鱼卵11215粒,仔鱼12645尾,隶属于4目、8科、36种,其中产漂流性卵鱼类24种.估算调查期间通过丰城段卵苗径流量为66.66×１０^８粒(尾),其中鱼卵径流量63.84×10^8 粒,鱼苗径流量2.82×10^8 尾;“四大家鱼”卵苗径流量为0.11×10^8 粒(尾),其中鱼卵径流量0.07×10^8 粒,鱼苗径流量0.04×10^8 尾.调查期间出现3次产卵高峰,集中在6 月上、中旬.各类群鱼卵数量呈现出不同的时间动态,银鮈(Squalidusargentatus)产卵高峰期主要出现在5月,银鲴(Xenocyprisargentea)、鳊(Parabramispekinensis)、赤眼鳟(Squaliobarbuscurriculus)以及“四大家鱼”则主要出现在6月.研究表明,峡江水利枢纽运行后,邻近峡江水利枢纽的巴邱“四大家鱼”产卵场消失,但其下游的仁和、新干产卵场保存较完整,在离坝较远的大洋洲镇江段新调查到一处“四大家鱼”产卵场.建议开展生态调度及增殖放流活动,以保护赣江鱼类资源.     

Embryonic and larval developments of brackish water catfish,Mystus gulio (Hamilton and Buchanan, 1822) induced with human chorionic gonadotropin and consequent larval rearing

Mystus gulio, the long whiskers catfish, is a popular food fish and potential candidate species for aquaculture in Sundarban area of India and Bangladesh. Recently, catch of this species has declined due to overfishing and various ecological changes. In the present study, mature fish was induced to spawn in captivity through intramuscular injection of human chorionic gonadotropin at the doses of 10 IU/g to female and 5 IU/g to male. Photomicrographs of all developmental stages of live embryo and larvae were documented with the aid of a light microscope. Results demonstrated that morula, blastula, gastrula and neurula and organogenesis ended at 1:30‐, 3:00‐, 5:30‐, 7:30‐ and 17:15‐hour post‐spawning (hps) respectively. Heartbeat and muscular contraction of embryo commenced at 8:30 and 11.15 hps respectively. Hatching of embryo started after an incubation period of 17:30 hour at an ambient temperature of 29 ± 1°C. The newly hatched larvae measured 2.17 ± 0.29 mm in total length with a yolk volume of 0.165 ± 0.03 mm³ started feeding 36 hr after hatching. The present study, on induced breeding and chronological development of M. gulio embryo, will have significant implications on conservation and seed production for aquaculture.     

Entry of adult Atlantic salmon into a tributary of the Aberdeenshire Dee,Scotland

Upstream counts of adult salmon in a tributary to the River Dee during autumn and winter were examined over a 13‐year period using an optical fish counter. Statistical analysis indicated that salmon were mainly primed to enter the tributary at a particular time of year, peaking at early December. However, environmental factors also had a large influence. Entry of salmon was initiated by high flow rates in the main stem of the River Dee. Increases in water level in the tributary itself were not needed to stimulate the entry of salmon. Moreover, a change in flow from 1 day to the next did not result in a response from salmon. Rather, they reacted only after more than a day of flow increase. There was no consistent threshold level of flow that triggered tributary entry. The upstream passage of salmon was reduced at low temperatures (below 3°C). The numbers of salmon migrating upstream showed a gradual increase as the temperatures increased up to 11°C, and then sharply decreased at higher temperatures. Female salmon migrated earlier by about 2 weeks on average than males. Increasingly, counters and traps are being installed on spawning tributaries to examine the state of salmon stocks. Caution should be exercised, however, in using upstream entry data from individual tributaries to provide an overall assessment of salmon abundance, as local conditions in the tributaries may affect the salmon counts in particular years.     

黄渤海蓝点马鲛繁殖群体渔业生物学特征研究

利用2016年4-5月、2017年4月在黄、渤海调查采集的350尾蓝点马鲛(Scomberomorus niphonius)繁殖群体的生物学数据,对该繁殖群体的生物学特征进行了分析研究。结果表明:该繁殖群体的叉长范围为406～1010 mm,体重范围为533～7245 g,年龄组成为1～10龄,其中1龄与2龄个体分别占总数的39.2%与33.7%。采用Von Bertalanffy生长方程表示其生长特性,生长参数分别为L_∞=1246.9mm,K=0.11;雌雄性比为1:1.49,3龄前雄性个体数占优势,3龄后雌性个体数占优势。蓝点马鲛的产卵期在4～6月,产卵盛期为4～5月;其绝对繁殖力范围为9.2～127.5万粒/尾,平均50.5万粒/尾;绝对繁殖力随着年龄、叉长的上升逐渐增大,7龄后出现衰退现象。蓝点马鲛的优势饵料生物为玉筋鱼(Ammodytes personatus)、细鳌虾(Leptochela gracilis)。与历史记录比较,蓝点马鲛低龄化、小型化现象更加突出,摄食结构改变,繁殖期提前,繁殖力水平有减小的趋势。     

注射LHRH-A2对刀鲚的催产效果及其雌鱼血液生化指标的影响

为了丰富刀鲚人工繁殖理论,探明LHRH-A2对刀鲚的催产效果及其雌鱼血液生化指标的影响,本研究以2冬龄人工养殖刀鲚为研究对象,通过注射LHRH-A2进行人工催产,并分析催产效果;同时应用放射性免疫、化学发光等方法,对人工催产过程中刀鲚雌鱼的血液生化指标进行了系统研究。结果显示,按照雌鱼30μg/kg、雄鱼减半的剂量注射LHRH-A2,刀鲚亲鱼死亡率为16.67%±3.34%;存活刀鲚亲鱼群体中,效应时间为21~24 h,催产率为83.33%±3.34%,受精率为75.06%±6.19%。注射催产素21 h内,血浆中17β-雌二醇(17β-estradiol,E2)、催乳素(prolactin)、甲状腺素(thyroxine,T4)、皮质醇(cortisol)、总蛋白(total protein,TP)、乳酸(lactate)在人工催产过程中表现出先上升后下降的规律;三碘甲腺原氨酸(three iodine thyroid,T3)、甘油三酯(triglyceride,TG)、Cl–呈现持续下降趋势;谷丙转氨酶(alanine transaminase,ALT)、谷草转氨酶(aspartate transaminase,AST)、渗透压(osmotic pressure)、K+、Na+呈现持续上升的趋势。比较以上血浆指标在产卵组和未产卵组的实验结果,产卵组形成高皮质醇、TP、TG、渗透压、Na+、K+的血浆环境和低E2、催乳素、乳酸、T4、T3、Cl-、ALT、AST的血浆环境,而未产卵组的这些指标与产卵组相反。结果表明,人工催产过程对肝脏、肾脏等正常功能造成了影响,从而抑制催产素LHRH-A2对卵子的正向调控作用。本研究初步揭示了人工催产应激对刀鲚雌鱼成功排卵的影响机制,为进一步优化刀鲚的规模化人工繁殖提供科学依据。     

Efficacy of 17 α‐methyl testosterone and letrozole on sex reversal of protogynous grouper,Epinephelus tauvina (Forskal, 1775) and spawning performance of sex‐reversed males

This study aimed to test the efficacy of 17 α‐methyl testosterone (17 α‐MT) alone and in combination with letrozole, an aromatase inhibitor, for the induction of sex reversal in protogynous greasy grouper, Epinephelus tauvina. Further, the long‐lasting effects of these treatments and spawning performance of sex‐reversed males were also investigated. Greasy grouper with oocytes in the perinucleolus stage were implanted with 5 mg 17 α‐MT kg^?1 body weight (T₁), 5 mg 17 α‐MT and 0.2 mg letrozole kg^?1 body weight (T₂) and 5 mg 17 α‐MT with 0.4 mg letrozole kg^?1 body weight (T₃) and no androgens/enzyme inhibitor implanted (C). The 17 α‐MT alone and in combination of letrozole‐induced sex reversal in greasy grouper, whereas untreated control fish (C) showed normal ovarian development. However, T₂ and T₃ group showed 100% sex reversal and completion of spermatogenesis up to functional male phase in 2 and 3 months, respectively, whereas T₁ group resulted in only 66.67% functional male with motile spermatozoa after 4 months. Sex‐reversed males successfully fertilized the eggs during induced spawning. There were significant differences on fertilization and hatching rates between T₂ group (79.00 ± 4.36%; 77.67 ± 2.87%, respectively) and T₁ group (57.67 ± 3.17%; 63.87 ± 2.91%, respectively). The result suggested that 17 α‐MT (5.0 mg kg^?1 BW) in combination with letrozole (0.2 mg kg^?1 BW) has the potential to produce 100% sex‐reversed male in short period in greasy grouper, which might greatly help in seed production of greasy grouper.     

Implications of using small meshed gillnets for the sustainability of fish populations: a theoretical exploration based on three case studies

The study explores the impacts of varying gillnet mesh size and fishing level on yield per recruit (Y/R), escapement spawning stock (ESS) and mega‐spawners (MS) of three widely distributed freshwater fishery target species. Y/R is maximised when the optimal length of capture (L_cap) is above the size of maturity (L₅₀). However, the unimodal shape of gillnet selectivity results in lower impacts to ESS and MS with both smaller and larger mesh sizes. Under conditions of moderate exploitation, the fraction of MS was significantly larger if small meshed gillnets were used. This is due to the relatively smaller cumulative vulnerability from small mesh sizes through time, as they target a smaller size range of fish, which also grow more quickly through the vulnerable window due to higher growth rates. Therefore, unlike trawls and beach seines, which select all size classes beyond the minimum length of capture (L_c), small meshed gillnets are not necessarily destructive and may rather promote sustained production by allowing a higher proportion of the spawning biomass to remain in the stock. The work also helps to explain the observation of sustained fish production in many developing countries despite the persistent use of gillnets of small mesh size that target small, under‐sized individuals.