光裸方格星虫繁殖习性的初步观察

2011年6、7、8月每月10日,挑选♀∶♂为5∶1的性成熟光裸方格星虫(Sipunculus nudus)亲体,在水泥池中暂养20 d,观察其产卵习性、产卵量及其体腔中生殖细胞的变化。结果表明,光裸方格星虫雌雄异体、体外受精;卵母细胞分批成熟,分批产卵;产卵时间不固定,昼夜皆可产卵,但夜间产卵次数和产卵量均高于白天;大量产卵时集群游动;6、7、8月的雌光裸方格星虫平均产卵分别为:3.20×104、4.43×104、3.46×104cell,平均受精率达98.3%;6、7、8月日累计产卵量y与时间x的变化方程分别为:y=0.430 5x3-25.971x2+503.39x-582.56(R2=0.982 0)、y=0.583 3x3-33.942x2+659.04x-712.43(R2=0.984 7)、y=-0.31x3+1.4676x2+245.11x-278.22(R2=0.994 3)。6、7、8月成熟卵细胞相对百分含量分别降低4.8%、9.0%、26.0%(P<0.01);6、7月的光裸方格星虫产后具有较好的再繁殖能力。     

福建莆田近海鲻鱼渔业现状及秋冬季产卵群体特点

本文主要根据2010年11月—2011年2月福建莆田近海流刺网作业鲻鱼生产调查资料,分析秋冬季渔获鲻鱼产卵群体组成、性腺成熟度分布等生物学特点及鲻鱼生产基本情况。结果表明:秋冬季(11月至翌年1月)是鲻鱼产卵盛期,也是鲻鱼渔业生产旺季;鲻鱼产卵群体主要为流刺网作业所利用,渔获群体优势叉长450～550 mm;近岸众多的流刺网作业过度捕捞亲鱼是造成鲻鱼资源量不断减少的主要原因之一。为更好地保护和利用莆田近海鲻鱼资源,建议进一步开展流刺网及张网作业对鲻鱼资源合理开发利用的专项调查研究。     

长江中游黄石江段四大家鱼早期资源现状

2015年和2016年每年的5—7月,在长江中游黄石江段对四大家鱼早期资源开展了调查,以了解该江段四大家鱼早期资源及产卵场分布现状。调查期间共采集四大家鱼卵67粒,苗23 948尾,种类以鲢和草鱼为主,分别占四大家鱼卵苗总捕捞数量的77.0%和18.1%。2015年和2016年,估算通过黄石江段的四大家鱼卵径流量分别为0.20×108粒、4.69×108粒,鱼苗径流量分别为19.40×108尾、13.65×108尾。黄石江段四大家鱼产卵场主要分布在团风李家洲、鄂州城区、鄂州戴家洲和黄石道士袱4个江段。与历史资料相比,黄石江段四大家鱼产卵场分布位置没有发生明显的变动。建议开展增殖放流活动,并在航道整治等工程建设中注重保护洲滩等生境。     

Effects of dietary keto-carotenoids (canthaxanthin and astaxanthin) on the reproductive performance of female rainbow trout Oncorhynchus mykiss (Walbaum)

The aim of this study was to clarify further the relationship between dietary keto-carotenoids (canthaxanthin and astaxanthin) and reproductive performance in female rainbow trout. Three experiments were undertaken in three successive breeding seasons. In addition to a control diet, fish were fed a canthaxanthin-supplemented diet (200 mg canthaxanthin kg⁻¹ feed, designated as 6mC200) for 6 months prior to spawning (experiment A); the same diet as in A but for either 3 months (3mC200) or 6 months (6mC200) before spawning (experiment B); diets with one of two levels of astaxanthin supplementation, 50 mg (6mA50) or 100 mg (6mA100) kg⁻¹ feed, or a diet with 100 mg canthaxanthin kg⁻¹ feed (6mC100) fed for 6 months (experiment C).
There was no significant influence of carotenoid supplementation on either the frequency of maturing females or the date of maturation. The number of ova per kg of female body weight averaged 2700 and did not vary significantly among fish fed the different diets. Across experiments A, B and C there was no significant difference in egg and larval survival among fish fed carotenoid-supplemented and control diets. In experiment A, 6mC200 females produced smaller eggs than controls but this result was not confirmed in experiments B and C. In general, eyed egg yield appeared partly dependent upon egg size. Alevin weight was also correlated with egg weight. The growth test conducted on fingerlings from experiment B failed to provide any evidence of an effect of feeding carotenoid supplemented diets to the female parent. Pigment analyses conducted on alevins revealed that canthaxanthin fed to the female parent was transferred into the eggs and therefore to the larvae, although canthaxanthin was metabolized within a few weeks after hatching.     

Sex organ extracts and artificial hormonal compounds as sex pheromones to attract broodfish and to induce spawning of Chinese black sleeper (Bostrichthys sinensis Lacépède)

Ovarian, testicular and seminal vesicle extracts of mature Chinese black sleeper (Bostrichthys sinensis Lacepede), synthetic steroids 17α‐progesterone (17α‐P), 17α,20β‐dihydroxy‐4‐pregnen‐3one (17α,20β‐P) and prostaglandins PGE₂ and PGF_2α were used in an attempt to attract broodfish and to induce spawning. Furthermore, 17α‐P, PGE₂ and PGF_2α levels were determined in extracts, and PGE₂ and PGF_2α levels were determined in holding and spawning waters. The results showed that ovarian extracts attracted more males than females to enter artificial nests, while testicular and seminal vesicle extracts attracted more females than males. The highest percentage of spawned nests were found when 17α,20β‐P and PGE₂ were administered to the nests, while the largest egg numbers and the mean highest fertilization rate were observed when PGE₂ was added. In ovarian extract, 17α‐P level was higher than levels in testicular or seminal vesicle extracts. The PGE₂ levels were significantly (P<0.05) higher than PGF_2α in the ovarian, testicular and seminal vesicle extracts. The PGE₂ and PGF_2α levels in spawning waters were higher than those in holding waters. The PGE₂ levels were greatly significantly (P<0.01) higher than PGF_2α in spawning and in holding waters. The results suggest that the sex organs of B. sinensis contain 17α‐P, 17α, 20β‐P, PGE₂ and PGF_2α and that 17α‐P, 17α,20β‐P and PGE₂ may act as sex pheromones in this species, attracting both male and female conspesifics to spawning sites and inducing spawning. Among the compounds tested, PGE₂ was the most effective sex pheromone for induction of spawning in B. sinensis.     

Reproductive performance of gilthead seabream (Sparus aurata L., 1758) fed two combined levels of carotenoids from paprika oleoresin and essential fatty acids

Despite carotenoids and essential fatty acids seem to play important roles in fish reproduction, no studies have yet been conducted to determine the effect of dietary carotenoids on gilthead seabream broodstock performance and their relation as antioxidants with dietary n‐3 highly unsaturated fatty acid (HUFA) levels. In addition, the high cost of synthetic sources of carotenoids is leading to the search for new natural carotenoid sources such as paprika oleoresin. Four experimental diets containing two combined levels of carotenoids from paprika oleoresin (40 and 60 mg kg^?1) and n‐3 HUFA (25 and 40 g kg^?1) were respectively fed to triplicate groups of gilthead seabream (Sparus aurata) broodfish. Elevation of n‐3 HUFA dietary levels from 25 to 40 g kg^?1 significantly improved gilthead seabream broodstock performance in terms of egg viability, hatching rates and fecundity. Besides, it markedly increased egg contents in HUFAs which play important energetic and structural roles and improve embryo development. Both arachidonic acid and eicosapentaenoic acid (20:5n‐3) egg contents were more readily affected by dietary n‐3 HUFA than docosahexaenoic acid. HUFA levels did not caused any negative effect suggesting an optimized content of antioxidants in broodstock diets. Increase in dietary carotenoids from 40 to 60 mg kg^?1 increased carotenoid contents in eggs and significantly improved egg fertilization rates suggesting an important sperm cell’s protective role by reducing the risk of lipid peroxidation which is detrimental for sperm motility. The increased inclusion of dietary paprika oleoresin enhanced egg carotenoid deposition and improved fish reproductive performance, denoting the high nutritional value of this product as a source of carotenoids for broodstock of this species.     

DNA barcoding reveals clear delineation between spawning sites for neritic versus oceanic fishes in the Gulf of Mexico

We combined research‐vessel cruises of opportunity with DNA barcoding to survey planktonic, percomorph fish eggs at 40 stations distributed across and around the Gulf of Mexico (GoM). The objectives were (a) to determine whether eggs of fishes that are potential candidates for the daily egg production method (DEPM) can be readily barcoded, (b) to identify taxa that are spawning in the GoM, (c) to determine encounter rates for eggs of economically valuable taxa, and (d) to characterize individual egg taxa as being primarily neritic, primarily oceanic, or primarily mixed (i.e., both neritic and oceanic). Of the 1,144 eggs that were individually barcoded, 709 (62%) were definitively identified to species (62 species from 42 families), with an additional 20 taxa identified to genus or subfamily level. The eggs of 15 economically important species were identified, most of which had intermediate encounter rates and moderately dispersed spatial distributions, as indicated by an index of aggregation. SIMPROF analysis of stationwise cluster analysis identified eight significant groups within the 35 stations that yielded percomorph eggs; a corresponding specieswise analysis identified six groups of stations as having a neritic egg community and two groups as having an oceanic community, with a community transition located at the shelf break. Although the neritic and oceanic stations did not share important species, it remains possible that coastal pelagic species have mixed neritic–oceanic distributions. Together, these results indicate DEPM fish‐egg surveys based on DNA barcoding are feasible at the large marine ecosystem scale.     

Seasonal movements of silver kob, Argyrosomus inodorus, (Griffiths and Heemstra) in Namibian waters

A seasonal migration pattern for silver kob, Argyrosomus inodorus (Griffiths & Heemstra) is elucidated based on tag-recapture data. Spawning adults start migrating southwards against the north-westerly surface currents at the beginning of the austral summer from the northern end of their distributional range to their spawning grounds, Sandwich and Meob Bays, at the southern end of their distributional range. It is suggested that after spawning larvae drift north with the current to the nursery areas, the West coast Recreational area (WCR). When juveniles reach the age of approximately 2 years they will gradually move north towards the adult feeding ground, the Skeleton Coast Park (SCP) waters. At the end of the spawning season when the surf-zone water temperature decreases to about 15 °C adult silver kob complete their spawning cycle by returning to the adult feeding ground, probably moving slightly offshore and with the current.     

Linking cod (Gadus morhua) and climate: investigating variability in Irish Sea cod recruitment

How climatic variability and anthropogenic pressures interact to influence recruitment is a key factor in achieving sustainable resource management. However, the combined effects of these pressures can make it difficult to detect non‐stationary interactions or shifts in the relationships with recruitment. Here we examine the links between climate and Irish Sea cod recruitment during a period of declining spawning stock biomass (SSB). Specifically, we test for a shift in the relationship between recruitment, SSB and climate by comparing an additive (generalized additive model, GAM) and non‐additive threshold model (TGAM). The relationship between recruitment success, SSB and the climatic driver, sea surface temperature, was best described by the TGAM, with a threshold identified between recruitment and SSB at approximately 7900 t. The analysis suggests a threshold shift in the relationship between recruitment and SSB in Irish Sea cod, with cod recruitment being more sensitive to climatic variability during the recent low SSB regime.     

Density‐dependent egg production in chub mackerel in the Kuroshio Current system

A paradigm of proportionality between spawning stock biomass (SSB) and total egg production (TEP) has been largely untested at multidecadal scales mainly because of difficulty in estimating annual TEP. Recently, this paradigm was directly tested for sardine (Sardinops melanostictus) and anchovy (Engraulis japonicus) at a multidecadal scale to reveal that SSB–TEP proportionality was partially distorted by intraspecific (sardine) and interspecific (anchovy) density dependence in total egg production per spawner individual (TEPPS) or unit weight (TEPPSW). In the present study, we demonstrate intraspecific density dependence in TEPPS/TEPPSW for chub mackerel (Scomber japonicus) in the Kuroshio Current system, using a proxy for TEPPS/TEPPSW, calculated from snapshot abundance data based on fishery‐independent egg surveys in combination with fishery‐dependent stock assessment data, at a multidecadal scale (38 years). TEPPS/TEPPSW exponentially declined with SSB, indicating a strong intraspecific density dependence in TEPPS/TEPPSW in chub mackerel. The observed phenomenon for chub mackerel was similar to that for sardine. Hence, intraspecific density dependence in TEPPS/TEPPSW may be a phenomenon that is generally applicable for species with a high maximum biomass and large population fluctuations. Lastly, we recommend the application of a TEP‐based framework to studies on recruitment mechanisms of fish.