Substrate composition determines emergence success and development of European nase larvae (Chondrostoma nasus L.)

European nase (Chondrostoma nasus) is a specialist riverine fish, characterised by a complex life cycle making it vulnerable to habitat degradation. Recent findings indicate that, analogously to salmonids, the interstitial zone quality may pose a serious bottleneck for successful recruitment of this species. In this study, nase eggs were exposed to different substrate qualities. First, standardised substrate mixtures with differing fine sediment additions were used. Second, we tested different homogenous gravel fractions for their influence on egg development and emergence success. In both setups, substrate composition significantly affected emergence success, timing of emergence and larvae size at emergence. In the substrate mixtures, emergence was most successful in substratum with no fine sediment addition (98%) and decreased to 55% in substratum with 20% fine sediment addition. Emergence was most successful in the coarsest fraction (93%) and decreased to 47% in the finest fraction. Over all treatments, the time between hatching and emergence from substrate differed by up to 156 degree days, thereby indicating that free embryos of nase use the shelter of the interstitial zone for early ontogeny. These results suggest that a loose and porous stream bed can positively contribute to the development success of eggs and larvae and thereby potentially improve the recruitment of nase populations. It is thus important to consider the substrate and interstitial conditions in the conservation and restoration management of this rheophilic cyprinid.     

Factors Influencing Early Survival and Growth of Laboratory‐reared Pacific Bluefin Tuna,Thunnus orientalis,Larvae

The collection of fertilized eggs for mass culture of Pacific bluefin tuna (PBT) relies on the spontaneous spawning of broodstock in captivity, and the spawning season of the broodstock is generally from mid‐May to September. The diameter of fertilized eggs from the broodstock decreases during the spawning season. To investigate the influence of three potential factors, the egg diameter (larger or smaller), the rearing water temperature (25 or 28 C), and the aeration rate during the night (strong or weak), on early survival and on growth of PBT larvae, replicate trials were conducted to assess these three factors until 7 d after hatching (d.a.h.). At 7 d.a.h., survival rates of larvae reared with strong nighttime aeration were found by a three‐way ANOVA to be significantly higher than for larvae reared with weak aeration. Furthermore, growth rates of PBT larvae hatched from larger eggs were significantly faster than those from smaller eggs. However, a significant difference in the survival rate was not detected for the factors, egg diameter and rearing water temperature. The results indicate that rearing with strong nighttime aeration significantly improved the early survival of PBT larvae and the egg diameter (a proxy for egg quality) and influenced growth.     

Predation on native fish eggs by invasive round goby revealed by species‐specific gut content DNA analyses

1. Conservation of riverine fish often aims to improve access to spawning grounds and restore longitudinal connectivity by removing migration barriers, and involves substantial investments. However, these investments also enable non‐native predators to invade upstream into spawning areas and potentially adversely affect the recruitment of threatened freshwater fish through egg or fry predation.
2. Detecting egg predation is often challenging. Visual inspections of fish gut contents may underestimate predation of soft materials such as eggs and fry, which limits the discovery of predators preying upon these life‐stages. DNA‐based detection assays may offer a more sensitive tool to assess predation of soft materials.
3. A conservation issue was confirmed by developing and applying a species‐specific DNA‐based detection assay: invasive round goby (Neogobius melanostomus) prey on the eggs or fry of the threatened common nase (Chondrostoma nasus) in Switzerland.
4. DNA‐based detection assays were also developed for five other valuable native fish species, including endangered salmonid and cyprinid river spawners. The applicability of the assays was confirmed in a series of laboratory and field feeding experiments involving eggs and fish tissue. In addition, this work provides a guiding framework for conservation managers regarding the use and applicability of different DNA‐based detection approaches for gut content analysis.
5. The results of this study could inform local conservation measures – such as temporary reductions in the density of round goby at spawning sites prior to spawning – and demonstrate how targeted application of species‐specific molecular markers may advance freshwater fish management.

     

Egg drift and hatching success in European river lamprey Lampetra fluviatilis: is egg deposition in gravel vital to spawning success?

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GnRHa‐induced Multiple Spawns and Volition Spawning of Captive Spotted Rose Snapper,Lutjanus guttatus,at Mazatlan,Mexico

Sexual maturation and induced spawning treatments were carried out with captive spotted rose snapper, Lutjanus guttatus. A total of 3013 × 10⁶ eggs (64.7% were floating) were produced from eight treated females in 42 spawns induced with GnRHa implants during the course of the present study. GnRHa ethylene‐vinyl acetate copolymer effective doses were 204 ± 11 µg/kg in June 2005, and 224 ± 13 µg/kg in July 2005. General fertilization was 50.9 ± 34.5% and 12–14 h after spawning, viability of floating eggs was 90.4 ± 12.4%. Mean incubation period at 29–31 C was 18–20 h, and mean hatching was 94.4 ± 8.2% (73–100%). Newly hatched larvae were 2.18 ± 0.15 mm in total length (TL). One month after the last hormone experiment, previously GnRHa‐treated and untreated fish began spawning voluntarily. Hormone‐treated breeders had higher fecundity than untreated fish, producing 72.5 million eggs versus 13.9 million eggs for the untreated fish, over the following 11 mo. Combined data of volitional spawning for total egg fertilization, viability, hatching, and larval TL were 77.7 ± 1.8%, 90.3 ± 1.3%, 87.9 ± 2%, and 2.50 ± 0.12 mm, respectively. These results can ensure the sustainability of a commercial hatchery.     

The influence of rearing temperature on early development and growth of spotted wolffish Anarhichas minor (Olafsen)

Temperature influenced the developmental rate, survival and early growth of eggs and embryos of spotted wolffish, Anarhichas minor (Olafsen), an interesting candidate for cold water cultivation. The total incubation period decreased from 220 days at 4 °C (880 daydegrees), to 177 days at 6 °C (1062 daydegrees) and 150 days at 8 °C (1200 daydegrees) in these experiments. The proportion of normal embryos and survival of eggs until hatching were highest when the eggs were incubated at 6 °C. During the incubation period, the embryo and yolk sac size at 280 daydegrees was not significantly different but at 850 daydegrees the embryo size was inversely related to temperature and the remaining yolk sac size positively correlated with the incubation temperature. The transformation of yolk to body mass during incubation appeared to be most efficient at 4 °C, and the embryos hatched with a larger visible yolk sac at 6 and 8 °C. The largest larvae (wet‐weight) hatched from the largest eggs and the egg groups incubated at the lowest temperature (4 °C). There was no effect of temperature on meristic characters. During 6 weeks post‐hatching, all larvae from the three temperature groups were fed formulated dry feed in excess at 8 °C in low water‐level raceway systems. During startfeeding, the larvae from eggs incubated at the lowest temperature (4 °C) showed the highest growth rates (SGR). Best survival of larvae was noted among batches incubated at 6 °C.     

Factors influencing the success of salmonid egg development in river substratum

Interstitial water conditions in the hyporheic zone of the stream bed are determinants of salmonid egg hatching success. We used standardised egg exposures to develop and validate discriminant analysis and generalised linear model models linking the hatching success of brown trout (Salmo trutta) with physicochemical factors of the interstitial zone (e.g., oxygen, specific conductance, nitrate, nitrite, ammonium, pH and redox potential). Interstitial water quality was identified as a limiting factor for egg development (median of relative hatching rates = 0.23). Hatching success was unimodal in hatchery and field references incubated in free‐flowing water, but bimodal (very high or very low hatching success) in natural sediment exposures. The effects of physicochemical factors on the hatching success of Salmo trutta strongly depended on both the time and spatial scale analysed. The variables retained in the models differed between the macroscale (over all rivers), the river‐specific scale (within a river) and the microscale (at different sediment depths). Egg hatching success decreased with increased substratum depth (decrease of 26% in 150 mm compared with 50 mm). Increasingly more variable interstitial water conditions (e.g., oxygen) throughout the egg incubation period suggest progressive degradation rates in the stream substratum during the incubation period at the microscale level. Consequently, consideration of different spatial and temporal scales is necessary for the evaluation of habitat quality in salmonid conservation and catchment management plans.     

盐度对杂交石斑鱼受精卵孵化和卵黄囊仔鱼形态及活力的影响

为了研究盐度对褐点石斑鱼(Epinephelus fuscoguttatus)♀×清水石斑鱼(Epinephelus polyphekadion)♂杂交后代(简称杂交石斑鱼)受精卵孵化、卵黄囊仔鱼形态及活力的影响,将杂交石斑鱼受精卵置于不同盐度水体中,观察盐度胁迫下卵径、油球径、孵化率及畸形率,以及孵化后卵黄囊仔鱼形态变化和活力状况。结果表明,在本研究条件下,受精卵卵径随盐度降低而增大,油球径不随盐度变化而变化。在盐度18~36范围内均能孵化仔鱼,但因盐度不同孵化率和初孵仔鱼畸形率有显著差异(P0.05);随盐度升高,孵化率呈先升后降的变化,初孵仔鱼畸形率则相反。盐度24~36组孵化后3 d仔鱼卵黄囊几乎完全消耗,组间无显著差异(P0.05)。在盐度24~36范围内,随着盐度的增加,仔鱼的不投饵存活系数(SAI值)呈先升后降的变化曲线;盐度30~33范围内,初孵仔鱼SAI值大于5;5日龄仔鱼全部死亡,半数死亡时间出现在孵化后3.5 d。综上分析表明,该杂交石斑鱼受精卵孵化及仔鱼培育的适宜盐度范围为24~36,最适盐度范围为30~33。     

温度、盐度对条石鲷胚胎发育影响及初孵仔鱼饥饿耐受力

研究了盐度、温度对条石鲷胚胎发育的影响和初孵仔鱼对饥饿的耐受力。结果表明,胚胎发育的适宜盐度范围为20～35,最适盐度范围为25～30,孵化率都在89%以上,盐度低于20或高于35,孵化率都降低。盐度对孵化时间有一定影响,盐度高于35或者低于15条件下孵化时间都延长。胚胎发育的适宜温度范围为21～27℃,孵化率都在77%以上,最适温度范围为23～25℃,孵化率达89%以上,低于19℃或者高于27℃时孵化率降低且初孵仔鱼畸形率升高。胚胎孵化时间与温度成负相关关系,胚胎发育速率与温度成正相关关系。条石鲷胚胎发育的生物学零度（阈温度）为10.06℃,有效积温值为405.3℃·h。对胚胎发育的Q10值进行了计算。饥饿条件下,条石鲷初孵仔鱼8日龄全部死亡,半数死亡时间出现在第6天,饥饿对初孵仔鱼生长具有明显的抑制作用。     

Rapid de-adhesion of northern pike <Emphasis Type="Italic">Esox lucius</Emphasis> eggs using sodium hypochlorite

The elimination of egg stickiness is required for effective artificial reproduction of northern pike, but until now, available methods have required at least 40 min. Sodium hypochlorite was tested under laboratory conditions, and exposure to aqueous concentrations of 0.025–0.05% for 40 s effectively eliminated stickiness without adverse effects. Fertilization and hatching rates in laboratory trials were similar to those observed in eggs treated with traditional methods using clay or milk for 40 or 60 min, respectively, as well as those without treatment. Testing using conventional hatchery incubation techniques did not reveal differences in fertilization rates, while the number of hatched larva was significantly higher in eggs treated with sodium hypochlorite vs. clay. Eggs treated with sodium hypochlorite retained transparency, which facilitated monitoring of embryo development.     

六线鱼人工育苗技术研究

使用从海区采集和人工催产获得的六线鱼卵块１０９１ｇ,孵化仔鱼１１万尾,平均孵化率为５６％,仔鱼经４５～６０天培育,育成全长２．５～４．０ｃｍ,鱼种１．８３万尾,平均成活率２４．４％,专家验收认为,育苗量,苗种规格及生长速度均处国内领先水平,对卵块收集,人工孵化,苗种生长,饵料系列,育苗病害,饵料生物培育等问题进行了研讨。     

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.     

Growth and recruitment dynamics of young‐of‐year northern pike: Implications for habitat conservation and management

Maximising growth during the months after hatching is critical for fishes to surpass predator gape limits, make ontogenetic shifts in diet and increase overwinter survival. Constraints on growth during early life stages can have population and community‐level implications, yet are rarely addressed by habitat restoration or fishery management efforts. To assess environmental controls on larval growth rates, we sampled adult and young‐of‐year (YOY) northern pike (Esox lucius) emigrating from spawning grounds in six tributaries of Lake Michigan. We found that YOY growth rates differed significantly among natal streams, in parallel with variation in hatch date and water temperatures. Within each stream, individual growth rates were positively associated with trophic position, as measured by nitrogen isotope enrichment and gut contents. Earlier hatching individuals also grew faster, but the strength of this relationship varied with warming water temperatures (i.e., 21–27°C). Ageing of adult spawners indicated no differences among streams in average growth rates later in life. Our findings suggest that restoration efforts should replicate ecological conditions found in habitats producing large numbers of fast‐growing YOY. Key habitat attributes include adequate water level throughout the spring spawning season, and stable, warm water temperature conditions. Providing these environments during early life history could enhance the robustness of northern pike populations by boosting fitness from hatching to emigration to adult habitats.     

梯级开发对家鱼产卵场高低流量过程的影响

产卵场特有的水力条件是四大家鱼繁衍的重要因素,尤其是流量脉冲引发的流速上涨是刺激家鱼产卵、保证鱼卵孵化的关键水力因子;流域梯级开发改变了天然河道的流量脉冲过程,导致产卵场破碎萎缩、鱼苗锐减。为揭示梯级开发对湘江干流四大家鱼产卵场水力特征的影响机理,建立了湘江干流家鱼产卵场二维数值模型,模拟了梯级开发前后典型高低流量脉冲过程,分析梯级开发对鱼类产卵场的影响。结果表明,梯级开发后,水流结构复杂性减弱甚至消失,高、低流速脉冲过程变得“尖锐”,流速上涨时间缩短50%（高流量脉冲）和67%（低流量脉冲）,高流量过程的 “喜好流速”或“触发流速”基本消失,低流量过程大部分流速均低于“腰点流速”;对流速上涨过程中平均流速分级水域面积统计表明,低于“腰点流速”面积分别扩大至3.0倍（Q高）和3.2倍（Q低）,“感应流速”范围水域面积减少至天然情况的15.8%（Q高）和1.2%（Q低）,“触发流速”范围面积减小至天然情况的1.5%（Q高）和1.6%（Q低）,“喜好流速”范围面积减小至天然情况的2.0%（Q高）和3.1%（Q低）。研究结果可为鱼类资源保护和恢复等措施提供参考和依据。     

曼氏无针乌贼胚胎发育的初步观察

将曼氏无针乌贼受精卵卵膜剥离,在显微镜或解剖镜下观察胚胎发育的全过程,结合室内人工育苗的孵化技术进行探讨。曼氏无针乌贼卵为粘性卵,呈黑色,类型属端黄卵,卵膜属三级卵膜,卵裂类型为不全卵裂,囊胚呈盘状,发生类型为直接发生型。在水温为23.8～26.2℃、盐度29.3时,最快14d孵出幼体,最慢23天孵出幼体,孵出幼体高峰期为18～21d,高峰期的孵出量占总孵出量的79.4%,孵化率为83.1%。胚胎发育速度与温度高低（20～30℃）成正比,盐度低于22对孵化率有严重影响。     

Volitional Spawning of Black Sea Bass Centropristis striata Induced with Pelleted Luteinizing Hormone Releasing Hormone-Analogue

The black sea bass is a high‐value marine serranid and is a prime candidate for intensive cultivation. Reliable methods for controlled spawning are needed to accelerate the development of hatchery technologies that result in mass production of healthy juveniles. During 1998–2001, spawning studies were conducted at The University of North Carolina at Wilmington (UNCW) and at the South Carolina Department of Natural Resources (SCDNR), Charleston, using pelleted luteinizing hormone releasing hormone analogue (LHRH‐a). From April through July 2001, 28 vitellogenic‐stage females, with mean oocyte diameters (MOD) ranging from 277–448 μm, were implanted with a 95% cholesterol‐5% cellulose pellet containing LHRH‐a (‐50 μg/kg body wt) at UNCW. In 10 individual spawning trials, females with MOD of 305–448 μm and maximum oocyte diameter × 475 μm spawned volitionally beginning 2–3 d post‐implantation (PI) and continued spawning over an average of 1.9 d (range = 1–4 d). Individual females released a mean total of 149,000 eggs (117,000 eggs/kg) with a mean buoyancy rate of 40.5% (floaters). Fertilization and hatching rates were 98% and 27.2% of floaters, respectively, yielding 14,600 yolksac larvae/female (12,600 yolksac larvae/kg body wt), and overall egg viability averaged 8.9%. In eight group spawning trials (2–3 females/group), average performance of females, including fecundity (103,800 eggs/female; 105,500 eggs/kg body wt), buoyancy rate (42.5%), fertilization and hatching rates (97.7% and 24.3% of floaters), numbers of yolksac larvae produced (10,900 yolksac larvae/female; 10,100 yolksac larvae/kg body wt), and overall egg viability (10.6%) was comparable to what was seen in individual spawning trials. From 1998–2000, a total of 58 vitellogenic stage (70% of oocytes 500 pm) females were implanted with pelleted LHRH‐a (‐50 μg/kg body wt) in nine group spawning trials (2–19 females/group) at SCDNR. Volitional spawning typically began 18–42 h PI and recurred every 1–3 d for an average duration of 9 d. Female groups released a mean of 560,000 eggs (84,000/female; 132,000/kg body wt) over the spawning period, with mean buoyancy rate of 25.7% floaters. Fertilization and hatching rates were 17.7% and 11.6 % of floaters, respectively, yielding 4,300 yolksac larvae/female (4,600 yolksac larvae/kg body wt). Overall egg viability was 2.9%. Captive wild‐caught black sea bass were induced to undergo repetitive volitional spawning by implantation of pelleted‐LHRH‐a, consistent with a multiple clutch group synchronous pattern of ovarian development. Group spawning appears to be a practical way to compensate for variable fecundity and egg viability of individual females. Research is needed to identify optimum hormone treatments and eligibility requirements.     

温度对奥尼罗非鱼受精卵孵化和仔鱼活力的影响

研究了温度对奥尼罗非鱼(Oreochromis niloticus×O.aureus)受精卵孵化和仔鱼活力的影响。在盐度为5不同温度(22、24、26、28、30、32和34℃)下,比较观察奥尼罗非鱼受精卵的培育周期、孵化周期、孵化率和畸形率。同时在以上不同温度条件下对初孵的奥尼罗非鱼仔鱼进行耐饥饿试验,测定其不投饵存活系数(Survivalactivity index,SAI)。结果表明:在温度为24~32℃,受精卵孵化率较高(84.3%~91%),温度高于34℃和低于22℃时,孵化率较低。温度与培育周期呈负相关关系,函数关系为y=0.3607x2-26.836x+553.5,R2=0.973。仔鱼生存适宜温度是24~30℃,最适的温度是24~26℃。温度为22℃时,SAI值分别为19.9,但是仔鱼发育的缓慢,部分仔鱼的身体色素一直没有出现,不适合仔鱼的培育。     

The first spontaneous spawning of European hake Merluccius merluccius L.: characteristics of eggs and early larval stages

For the first time, a spontaneous spawning of hake was recorded in Spain in April 2009. The spawn was obtained from broodstock kept in captivity for two years at the facilities of the Spanish Institute of Oceanography in Vigo (NW Spain). Eggs were transparent, spherical and had an average diameter of 1.067 ± 0.024 mm; yolk occupied the majority of egg volume. The oil droplet had a diameter of 0.27 ± 0.03 mm. The incubation period of the eggs lasted for 4 days at 14°C and the duration from hatching to the total absorption of the yolk sac was between 5–7 days after hatching, at the same temperature. Newly hatched larvae had an average total length of 3.20 ± 0.13 mm and began feeding 6 days after hatching; a daily growth rate of 0.158 mm day‐1 was observed from hatching to yolk sac consumption. This paper describes the daily evolution of biometric and morphological characteristics of the different stages of embryos and larvae of European hake up to the age of 19 days.     

Hatching time effect on the intra‐spawning larval morphology and growth in Northern pike (Esox luciusL.)

Based on the analysis of 11 morphometric variables of body (total length, body area and perimeter, myotome height and eye diameter) and yolk sac (length, height, area, perimeter and volume) of pike larvae, the aim of this study was to evaluate how larval size at hatching and growth of larvae hatched from single egg batches vary according to three hatching times: early, mid and late. Hatching time structures strongly pike larval morphometrics. Early hatched larvae have smaller body sizes at hatch, faster growth and higher yolk use efficiency than late hatched ones. Early hatched larvae seem to be premature and hatch at precocious developmental stage whereas late hatched individuals continue their growth within the egg shell and hatch at larger size but with lower reserves (yolk). A compensatory growth phase was observed for the early hatching pike larvae particularly during the first 5 days post hatch. Consequently, no significant difference in body parameters was recorded from day 10 post hatching whatever the hatching time. The higher growth accomplished by early hatched larvae may be related to a particular metabolic activity that converts more efficiently yolk into body tissues.     

基于鱼卵仔鱼数据的东海中南部日本鲭产卵场分析

利用2016年4—5月在东海中南部海域的调查数据,对该海域日本鲭(Scomber japonicus)鱼卵仔鱼的分布特征进行了研究,并对产卵场的划分展开讨论及提出保护措施和管理建议。结果显示:4月,日本鲭鱼卵仔鱼主要出现在台湾海峡和东海南部海域,出现率均大于25%,但仔鱼在东海南部外海的出现率和丰度均较低,分别为5.00%和0.01个·100m-3。5月,日本鲭鱼卵仔鱼在台湾海峡的出现率和丰度均显著降低,分别下降至5.88%和0.22个·100m^-3;东海南部外海日本鲭鱼卵仔鱼的出现率和丰度则均显著升高,分别升至50%和36.48个·100m^-3,其中鱼卵集中出现在南部外海,出现率和丰度分别达到了40%和36.46个·100m^-3;东海中部外海从5月开始出现日本鲭鱼卵和仔鱼。结合历史资料,可以判断东海中南部日本鲭产卵场主要有台湾海峡、东海中南部近海、东海南部外海、东海中部外海等4个。日本鲭鱼卵丰度与表层水温呈显著相关关系(R=0.37,P<0.05),与表层盐度无显著相关关系(P>0.05);仔鱼丰度与表层水温及表层盐度均无显著相关关系(P>0.05)。结果表明,水温对日本鲭的产卵活动影响较大,随着水温的逐步升高,性腺发育速度加快,开始产卵的亲体数量也大量增加,这从鱼卵仔鱼的数量大量增加得以体现;而盐度变化对日本鲭的产卵活动影响相对较小。针对日本鲭不同的产卵场,建议制定差异化的繁殖亲体和幼鱼保护措施。