Variation in reproductive potential and influence on Icelandic herring recruitment

Explaining recruitment variation in fish is essential for successful fishery management and is consequently under constant review, with an increasing focus on how maternal factors, relative to environmental influences, operate at the level of individual female spawners and extend from the spawning stock through to recruitment. We estimate total egg production (E) in Icelandic summer‐spawning herring (Clupea harengus) from 1963 through 1999 by using sequential population analyses (SPA) and their estimates of stock biomass and recruitment, various size and maturity metrics, and individual fecundity estimates that rely on total length and the condition of the spawners. Generalized linear models indicate that maternal effects are of significance in explaining SPA‐based recruitment‐at‐age‐3 (R). The best model explained 64% of the variation in R and incorporates E constrained to the repeat spawners (40%), the NAO winter index (18%) and ocean temperature (6%). The latter two represent the winter and spring periods subsequent to year‐class formation. Recruit spawner contributions to E were of no significance in explaining variation in R despite the fact that they could contribute as much as 55% of E when their contribution to E was consistently underestimated by a factor of ～ 2, based only on their contribution to spawning stock biomass. We conclude that the spawning potential of the repeat spawners should replace total spawning stock biomass for determining recruitment potential in stock assessment. In addition to the incorporation of oceanographic factors, this would provided a more cautious and risk‐adverse approach.     

Chironomid abundance and consumption by juvenile channel catfish in plastic‐lined and earthen culture ponds

In 2004, research was conducted to compare chironomid larvae populations and their use by channel catfish (Ictalurus punctatus) fingerlings in two different culture systems. Over a 4‐month culture period, chironomid larvae densities in plastic‐lined ponds were significantly less than those in earthen ponds. The consumption of chironomid larvae by channel catfish fingerlings was related to chironomid abundance in earthen ponds. The significance of these findings is the possible relationship among pond type, initial consumption of commercial diets and subsequent survival rates of fingerling channel catfish.     

An intensive hatchery rearing protocol for larvae of the bullseye puffer,Sphoeroides annulatus (Jenyns)

In this study bullseye puffer, Sphoeroides annulatus larvae were reared from hatching through to 1 or 2 months after weaning on an experimental scale in three replicate 600 L tanks and on three occasions during the spawning season (nine tanks in total). The rearing protocol used was green water (Nannochloropsis oculata and Isochrysis sp.) 100 000 cells mL^?1 from 0 to 11 days after hatch (DAH), 5–10 rotifers, Brachionus rotundiformis mL^?1 from 2 to 26 DAH, 0.1–1 Artemia mL^?1 from 21 to 34 DAH and weaning from 29 to 34 DAH. Survival to a month after weaning was 1%, a total of 3153 juveniles were produced with an average wet weight of 0.29 ± 0.07 g and a length of 27.5 ± 0.82 mm.     

Reproduction and recruitment of the brown shrimp Crangon crangon in the inner German Bight (North Sea): An interannual study and critical reappraisal

The brown shrimp, Crangon crangon, is the most important target of the coastal crustacean fisheries in the German Bight. In order to evaluate the relation between the abundance of ovigerous females and larvae in spring and the recruitment success in autumn, we first analysed the seasonal appearance of ovigerous females and larvae from weekly samples throughout 2012. The spawning season in the German Bight extends over several months comprising multiple unsynchronized spawning events. The minimum shares of ovigerous females appeared in early autumn, and the highest shares in late winter bearing mostly early egg stages. We defined the putative start of the reproductive cycle for November when the frequency of ovigerous females started to increase. There was no distinct separation between winter and summer eggs, but a continuous transition between large eggs spawned in winter (the early spawning season) and batches of smaller eggs in spring and summer. Larval densities peaked in April/May. Consequently, regular annual larval surveys from 2013 to 2016 were scheduled for April/May and extended to six transects covering the inner German Bight. Ovigerous females were most abundant in shallow waters above the 20‐m isobaths, which also explained regional differences in abundance between the regions off North Frisia and East Frisia. No relation was obvious between the number of larvae in spring and recruited stock in autumn. Due to the short lifespan of C. crangon, the combination of various abiotic factors and predator presence seems to be the principal parameters controlling stock size.     

Effect of dietary DHA/EPA ratio on the early development,antioxidant response and lipid metabolism in larvae of Siberia sturgeon (Acipenser baerii,Brandt)

A 30‐day growth study was conducted to evaluate the impacts of the dietary DHA/EPA ratios on growth performance, antioxidant and lipid metabolism of Siberian sturgeon larvae. Four isonitrogenous and isoenergetic microcapsuled diets were formulated with various DHA/EPA ratios as 0.73 (R_0.73), 1.25 (R_1.25), 1.75 (R_1.75) and 2.33 (R_2.33). The results showed that the final body length, final body weight, specific growth rate and survival in the group R_2.33 were highest (p < 0.05), while there were no significant differences on viscerosomatic index and condition factor among all groups. Visceral catalase activity of groups R_2.33 and R_1.75 was significantly higher than that of groups R_0.73 and R_1.25, but superoxide dismutase, total antioxidant capacity, malondialdehyde, total cholesterol, triglycerides and high‐density cholesterol were not different among groups. The gene expression of PPARα and lipoprotein lipase had no difference among groups, but the expression of hepatic lipase gene in groups R_1.75 and R_2.33 was significantly lower than that in group R_0.73 as a negative feedback of high dietary DHA intake. In conclusion, growth performance was improved but kept stable antioxidant response in visceral mass with increased levels of DHA/EPA ratios from 0.73 to 2.33 for Siberian sturgeon larvae. Improving DHA/EPA ratios is a benefit for larvae to selectively deposit more DHA, then EPA and ARA than MUFA in the body to meet the requirement for early development.     

Change in nutrient composition of Artemia grown for 3–4 days and effects of feeding on‐grown Artemia on performance of Atlantic halibut (Hippoglossus hippoglossus,L.) larvae

Major challenges in culture of Atlantic halibut larvae have been slow growth during the late larval stages and inferior juvenile quality due to pigmentation errors and incomplete eye migration during metamorphosis. The hypothesis of this study was that feeding on‐grown Artemia would alleviate these problems. Artemia were grown for 3–4 days on Origreen or Origo. The growth and nutrient composition of Artemia nauplii and on‐grown Artemia were analysed, and both Artemia types were fed to Atlantic halibut larvae, on‐grown Artemia from 15 days post‐first feeding (dpff). The body length of Artemia increased with 20%–70% in response to on‐growing. In all experiments, protein, free amino acids and the ratio of phospholipid to total lipid increased, while lipid and glycogen decreased. The fatty acid composition improved in some cases and not in others. The micronutrient profiles were not negatively affected in on‐grown Artemia. All these changes are thought to be beneficial for marine fish larvae. The final weight of Atlantic halibut postlarvae was similar, and 90% of the juveniles had complete eye migration in both groups. It is concluded that the present version of Artemia nauplii probably covers the nutrient requirements of Atlantic halibut larvae.     

黑点青鳉的生长和摄食行为发育

针对黑点青鳉实验室养殖成活率低的问题,对其摄食行为发育进行研究,了解其早期阶段的摄食行为发育状况,为人工养殖提供理论依据。通过单摄像机结合镜面成像的方法,对黑点青鳉胚后发育阶段90 d摄食行为的观察与分析,研究了投喂卤虫无节幼体条件下黑点青鳉的生长特征和摄食行为发育。结果显示,幼体体长平均生长率为2.579%/d,体长与日龄间关系为y=3.132+0.383x-0.004x^2+0.00003x^3,R^2=0.98。通过各项摄食行为指标将其幼体生长发育分为3期6个阶段:仔鱼期(0~10 d)分为前仔鱼期(0~4 d)和后仔鱼期(5~10 d),稚鱼期(11~30 d)分为前稚鱼期(11~18 d)、中稚鱼期(19~24 d)和后稚鱼期(25~30 d),幼鱼期(31~65 d)。黑点青鳉幼体出膜4 d后开始投喂初孵卤虫,至10 d所有鱼苗均能捕食。黑点青鳉仔鱼期幼体死亡率较高,但摄食能力稳步提升,至该期末,摄食成功率提升至45%~55%,摄食效率达0.5~0.6个/min;稚鱼期幼体的各项摄食指标均有大幅度提升,对饵料的响应时间不断缩短,摄食速率提高,响应距离也逐渐增长,摄食量增大,摄食成功率已提升至90%~95%;幼鱼期各项摄食指标已接近成鱼,摄食效率达9个/min以上,摄食功能已趋于完善。研究表明,黑点青鳉在仔鱼期对卤虫无节幼体的响应距离短、摄食速率低下,摄食成功率与摄食效率均处于较低水平,随着其自身的发育以及摄食能力的稳定提升,摄食成功率和摄食效率逐步提高,成活率趋于稳定。养殖期间,通过密切注意黑点青鳉的摄食行为变化,改变投喂的数量和频次,使更多的仔鱼尽快过渡到稚鱼期,可能是提高养殖成活率的一条有效途径。     

基于Bayes判别法的马尾松毛虫一代、二代幼虫发生期的预报

为了提高马尾松毛虫Dendrolimus punctatus(Walker)发生量预测预报结果的准确性,本文运用Bayes判别分析法建立安徽省潜山县1983年-2016年33年的马尾松毛虫一代和二代幼虫发生期的预报模型。一代幼虫发生期的判别函数方程为:f(1)=-15744.058-361.501x1+60.759x2+133.502x3+511.368x4;f(2)=-16854.938-375.596x1+70.405x2+132.608x3+529.690x4;f(3)=-17645.295-384.956x1+73.601x2+134.955x3+541.782x4;f(4)=-18179.639-382.408x1+71.342x2+135.234x3+549.655x4对1983年-2018年一代幼虫发生期预报结果历史符合率为97.06%,二代幼虫发生期的判别函数方程为:f(1)=-134898.483+559.235x5+113.112x6-250.033x7+1461.350x8;f(2)=-138908.622+573.572x5+118.340x6-252.691x7+1474.569x8;f(3)=-141430.680+577.358x5+125.727x6-254.610x7+1483.336x8;f(4)=-143185.175+578.968x5+129.628x6-256.102x7+1491.257x8对二代幼虫发生期的预报结果的历史符合率为100%。对2017年和2018年的验证回报,与实况结果一致。筛选出对预报量有密切关系的预报因子是本方法预报准确性的关键,该方法是一种简便准确性高的预报方法。