Effects of feeding live or frozen prey on growth, survival and the life cycle of the cuttlefish, Sepia officinalis (Linnaeus, 1758)

The effects of feeding live or frozen grass shrimp (Palaemonetes varians) to the cuttlefish, Sepia officinalis, were determined in two experiments. During Experiment I, two populations of 30 cuttlefish (aged 90 days old) were fed either live or frozen grass shrimp. Cuttlefish fed live shrimp grew larger, matured earlier, had a shorter life cycle (255 days) than the ones fed frozen shrimp (282 days), and had lower mortality. Females from the group fed frozen shrimp matured a month later but were significantly larger, 130.9 ± 38.5 g, compared to 74.2 ± 16.0 g, laid larger eggs, 0.47 ± 0.11 g, compared to 0.28 ± 0.10 g, and had higher individual fecundity (411 eggs female⁻¹, compared to 150 eggs female⁻¹). Newly born hatchlings from both groups had similar weights. During Experiment II, six replicates of 15 cuttlefish (50 days old) were used, three for each of the two diets tested. The exact same amount of live or frozen shrimp was provided to both populations twice a day. No differences in growth and feeding rates or food conversions were found at the end of the experiment. During the first week, cuttlefish fed frozen shrimp grew larger, and had higher conversion rates, compared to the ones fed live shrimp. Mortality was higher for the group fed live shrimp (36.6%) in Experiment II, mainly occurring during the last week. Mortality for cuttlefish fed frozen shrimp in Experiment II was 2.2%. Results obtained here indicate that freezing the grass shrimp only had a negative effect on the survival of S. officinalis in Experiment I. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of Using Live Grass Shrimp (Palaemonetes varians) as the only Source of Food for the Culture of Cuttlefish, Sepia officinalis (Linnaeus, 1758)

The life cycle of cuttlefish fed ad libitum exclusively on live grass shrimp (Palaemonetes varians) was studied during 5 consecutive generations. Different culture temperatures promoted different (P < 0.05) exponential growth for each life cycle, being summer generations shorter than those of winter. Higher temperatures promoted higher IGR’s and mortality, while lower temperatures promoted increased life span, reproduction stages, total fecundity and total egg biomass. Increased generations also seemed to increase fertility. A “hybrid” generation promoted the best results in terms of hatchling weight, individual fecundity and fertility. Mean egg weight was related to female size and embryonic development took longer at lower temperatures. Brood stock sex ratios seemed to be temperature related. All of these culture aspects were also compared between themselves in order to establish future brood stock methodologies. Grass shrimp proved to be a good diet for the culture of cuttlefish throughout the life cycle. The use of only one species reduces costs and labor associated to cuttlefish culture.     

Aspects of the growth of cultured cuttlefish Sepia officinalis (Linnaeus 1758)

Feeding rates, growth rates and feed efficiency ratios were studied in experimentally reared juvenile cuttlefish Sepia officinalis which had been hatched from eggs collected from three different locations, Plymouth, North Wales and Southampton. Groups of newly hatched cuttlefish were either maintained at 19°C and well fed (experiment 1) or were maintained at ambient seawater temperature (7–16°C) with little food for 6 months so that their development was delayed and then transferred to optimum conditions (experiment 2). In the first investigation (expt 1), no significant differences in growth rates (3.72±0.08%, 3.75±0.04% and 3.55±0.04% body weight (BW) day^?1 respectively), feeding rates (9.53±0.36%, 9.28±0.36% and 8.95±0.37% BW day^?1 respectively) and feed efficiency ratios (38.11±1.67%, 40.52±1.78% and 39.96±1.78% respectively) were observed between cuttlefish from the 3 locations. During the second investigation (expt 2), cuttlefish, whose development was initially delayed after hatching and then were stimulated to grow under optimum conditions (19°C and fed), showed growth rates (3.46±0.08% BW day^?1) similar to those held under optimum conditions of seawater temperature (19°C) and food supply shortly after hatching. Feeding rates and feed efficiency ratios were however significantly higher in cuttlefish maintained at 19°C compared to 11°C (8.27±0.14% BW day^?1, 41.25±0.52% and 2.75±0.09% BW day^?1, 24.87±1.87% respectively).     

The effects of tank colours on the growth and survival of cuttlefish (Sepia officinalis,Linnaeus 1758) hatchlings and juveniles

The effects of different tank colours (white, yellow sandy and black) on the growth, mortality and biomass production were studied for hatchling and early juvenile cuttlefish. For hatchlings, the use of different colour tanks did not promote differences in growth due to the higher variability (standard deviation) found in the white‐ and sand‐coloured tanks. Black tanks promoted the lowest and highest values for total mortality and biomass respectively. For juveniles, the use of different tank colours promoted different growth (P<0.05), but not mortality. Black tanks promoted the best results in terms of growth and biomass. The results obtained in the present study advise the use of black (or dark colour) tanks in the hatchling and early juvenile stages to reduce the standard deviations associated with growth, mortality and biomass production. This will contribute to minimize problems associated with slow and fast growers and competition.     

Growth of young cuttlefish, Sepia officinalis (Linnaeus 1758) at the upper end of the biological distribution temperature range

Individual growth rates, feeding rates (%BWd^?1) and food conversions for cuttlefish (S. officinalis) hatchlings and juveniles were determined during this study. A flow‐through system was used. Water temperature reached 30 °C during the hottest part of the day, gradually decreasing to 25 °C during the night; salinity varied between 37 ± 3 ppt and lights were kept on for 14 h day^?1. Hatchlings were placed in separate compartments with a water volume of 1.2 L. Juvenile cuttlefish (from 0.5 to 25 g) were placed in bigger baskets, with a water volume of 5.2 L. Water flow was 120 L h^?1. The biggest cuttlefish used in these experiments (> 25 g) were gathered in groups of five and placed in circular tanks (water volume of 250–300 L). Thus, results obtained in this case are means and not individual data. During the first 10, 20, 30 and 40 days, mean growth rates (of all individuals sampled by age group) decreased consistently (11.8 ± 4.1, 9.8 ± 1.8, 8.1 ± 2.2 and 7.3 ± 0.7%BW^?1 respectively); in similar fashion, mean feeding rates decreased with age group (33.7 ± 13.5, 22.0 ± 7.9, 17.3 ± 3.9 and 16.7%BWd^?1 respectively). Mean food conversions varied between 3.6 and 2.5 between the age groups. When grouping results by weight class, similar patterns occur, as growth and feeding rates decrease consistently as cuttlefish grow bigger. Highest mean growth and feeding rates are obtained by hatchlings (< 0.1 g) with 12.4 ± 4.5 and 35.3 ± 15.1%BWd^?1, respectively, while the lowest growth and feeding rates were recorded for the largest animals, between 15 and 25 g (3.4 ± 1.1 and 10.8 ± 4.1%BWd^?1 respectively). For these weight classes, mean food conversions varied between 2.7 ± 0.9 and 3.8 ± 2.8.     

金乌贼荧光标志方法的研究

建立一种简单实用的标志方法,对更好地评价金乌贼增殖放流效果和渔业资源现状非常重要.以金乌贼为实验对象,利用荧光物质茜素络合指示剂(Alizarin Complexone,ALC)浸泡金乌贼幼体,对其内壳进行标志,所用荧光染色剂浓度为(6.0～8.0)×10-3%,浸孢染色时间24 h.将标志组和对照组的金乌贼幼体分别暂养于1.5 m×1.5 m×1.5 m水泥池30 d,后将暂养的幼体放养于面积为2 667 m2的室外土池,并在60 d后,将平均胴背长达91.4mm(对照组)、87.6 mm(标志组)金乌贼幼体移入室内水泥池越冬,整个实验历时210 d.实验期间,分别在标志后15、30、45、60、90、210 d对金乌贼进行随机取样,解剖出内壳观察标志色保留状况并对金乌贼生长发育及存活率进行测量.结果显示,标志金乌贼的成活率为100%;方差分析显示,标志组和对照组金乌贼的生长发育差异不显著(P0.05);210 d后内壳骨针部仍清晰保留初染时的半椭圆形淡紫色圆圈;实验所采用的ALC内壳标志方法操作容易,可一次性大量进行标志处理,鉴别简单,无需借助其它仪器,肉眼便可直接观察到标志色,并且标志色保持率高,保留时间长,是一种理想的标志金乌贼的方法.     

Effects of live prey availability on growth and survival in the early stages of cuttlefish Sepia officinalis (Linnaeus, 1758) life cycle

This investigation examined the effects of live prey availability on growth and survival of Sepia officinalis. Two independent experiments, comprising two feed rations each, were performed, using adequate prey size. In the first experiment, cuttlefish hatchlings were fed live mysids, Paramysis nouvelli [(feed ratio I (fr I)], at 15% body weight per day (bw day^?1) (fr I₁₅) and 30% bw day^?1 (fr I₃₀). In the second experiment, juvenile cuttlefish were fed live Atlantic ditch shrimp, Paleomonetes varians (fr II), under the same experimental design. In both experiments, the final mean weight, feeding rate and instantaneous growth rate were higher when animals were fed feed ratio fr II₁₅ and fr II₃₀ (30% bw day^?1). The results indicate that prey availability influenced weight gain, irrespective of the prey used, during the first 2 months of cuttlefish life cycle. This effect seems to be more noticeable when a certain limit of prey is achieved. For cuttlefish fed fr II, the optimal prey density is thought to be under 2.5 g prey L^?1 (i.e. 14 shrimp L^?1). Results indicate that cuttlefish can withstand prey densities up to 120 mysids L^?1 for cuttlefish up to 3 weeks old and 19 shrimps L^?1 for cuttlefish up to 6 weeks old.     

金乌贼幼体弧菌性坏死病的病原、组织病理特征和药物敏感性

对青岛市黄岛区人工繁育金乌贼(Sepia esculenta)苗种大规模坏死病进行了病原、组织病理、传播途径和防控药物研究。发病金乌贼幼体不摄食,生长缓慢,体色发黑;体表、肌肉、口腕、触腕及内脏团大面积溃烂,死亡率高达90%;组织病理学显示:患病金乌贼皮肤色素细胞崩解,肌丝断裂,鳃丝崩解,肝细胞大量坏死脱落,肠道微绒毛脱落;从患病金乌贼分离出3株优势菌(SE-A、SE-B和SE-C),人工感染实验表明,SE-B、SE-C对金乌贼半数致死量分别为3.98×10~6 CFU/mL和8.91×10~5 CFU/mL,有较强致病力,为该病的致病菌;根据细菌形态、生理生化和16S rDNA序列分析将SE-B和SE-C鉴定为溶藻弧菌(Vibrio alginolyticus)和塔氏弧菌(Vibrio tubiashii)。分析金乌贼幼体、育苗用水和生物饵料糠虾的病原菌来源、分布和优势度,发现致病菌主要由糠虾携带进入育苗系统。分析了2株致病菌的药物敏感性,SE-B对强力霉素和氟苯尼考等敏感,对链霉素、庆大霉素等耐药;SE-C对氟苯尼考和罗美沙星等敏感,对新霉素和克拉霉素等耐药。     

Effect of Artificial Diets on Growth,Survival and Condition of Adult Cuttlefish, <Emphasis Type="Italic">Sepia officinalis</Emphasis> Linnaeus, 1758

The effects of artificial diets on growth and body condition of adult cuttlefish, Sepia officinalis were tested in two experiments. Supplemented prepared diets (fish myofibrillar protein concentrate) were fed during a 30-day and a 21-day experiments. Growth, feeding rate and food conversion of group-reared cuttlefish were analyzed. The first of these experiments tested four artificial diets, made with increasing levels of lysine, on adult cuttlefish. According to the chemical analysis, diets 1–3 had limiting concentrations of lysine and other essential amino acids (compared to mantle composition of the cuttlefish), while diet 4 was the only one where almost all essential amino acids were present in concentrations similar or higher than the ones present in cuttlefish mantle. A second experiment was conducted by isolating 16 adult cuttlefish individually, and feeding them the same four artificial diets, in order to obtain individual data. During Experiment 1, only the diet with the best chemical score (diet 4) produced growth (p < 0.05), with a mean instantaneous growth rate (MIGR) of 0.30% wet body weight (BW) d⁻¹. Similarly, individually reared cuttlefish fed diet 4 produced the highest IGR’s (0.26, 0.38 and 0.48% BW d⁻¹) and grew larger (p < 0.01). Comparison of cuttlefish fed the artificial diets vs. thawed shrimp and unfed cuttlefish indicated that cuttlefish fed the artificial diets were in an intermediate state. Growth rates obtained with the artificial diets (<0.4% BW d⁻¹) were considerably lower compared to natural prey, live or frozen, reported by other authors.     

Effects of prey nutritional quality on the growth and survival of juvenile cuttlefish, Sepia officinalis (Linnaeus, 1758)

This investigation examined the effect of prey condition on the growth and survival of juvenile cuttlefish ( Sepia officinalis ). In the first group, cuttlefish were fed with daily captured live Palaeomonetes varians from the wild [daily prey (DP)], the second group was fed 5 days stocked and starved P. varians [starved prey (SP)], while in the third group, cuttlefish were fed 8 days stocked P. varians fed with an artificial diet [fed prey (FP)]. Mean instantaneous growth rate (IGR) was 2.8±1% body weight day⁻¹ (bw day⁻¹), 3.3±1.1% bw day⁻¹ and 4.9±0.5% bw day⁻¹ for SP, DP and FP respectively. At the end of the experiment, final weight gain ( W _g) was 121±21.6%, 153.8±17.3% and 295±29.8% for SP, DP and FP respectively. No significant differences were found ( P >0.05) between growth curves for every group tested, or for the food conversions between those same groups ( P >0.05), but statistical differences ( P <0.05) were found in IGR between DP vs. FP and SP vs. FP. Mortality was 2 and 1 for SP and DP respectively. Results indicate that prey starvation should not be considered when feeding juvenile cuttlefish, as prey can only be stocked if proper artificial diets are provided, to obtain optimal growth.     

First multi-generation culture of the tropical cuttlefish Sepia pharaonis Ehrenberg, 1831

Sepiapharaonis, the pharaoh cuttlefish was cultured through multiplegenerations in the laboratory (5 consecutive generations) using closed,recirculating water filtration systems. The eggs of the original parentalgeneration (G_P) were spawned by a wild caught Gulf of Thailandfemale in alocal fisheries laboratory, then packed and shipped air cargo to Texas wherehatching occurred. The culture temperature ranged 25°–28°C, except for one generation that was chilled intentionallyto21 °C and then warmed to 25 °C after 9.6months. Spawning occurred as early as day 161. Spawning output was high in allgenerations except the group that was cultured at 21 °C. Eggfertility was low in captivity (< 20%), but hatchling survival was high(>70%). The average egg incubation time was 13.6 d at 25–28°C. The largest spawn resulted in 600 viable hatchlings andthesmallest resulted in 11 hatchlings. The cuttlefish ate a wide variety ofestuarine crustaceans and fishes as well as frozen shrimp. There were noapparent disease problems since survival from hatching to maturity was over70%.The average life span for cuttlefish cultured at 25–28°Cwas 8.9 months and 12.3 months at 21 °C. Size at hatching wasmeasured for fourth generation (G₄) hatchlings; the mean weight athatching was 0.103 g and the mean mantle length was 6.4mm. The largest cuttlefish cultured was a male 300 mmML and 3,045 g; the oldest cuttlefish lived 340 d.This cuttlefish species presents an excellent choice for commercial mariculturebecause of its rapid growth, short life span, tolerance to crowding andhandling, resistance to disease and feeding habits.     

The use of Artemia sp. or mysids as food source for hatchlings of the cuttlefish (Sepia officinalis L.); effects on growth and survival throughout the life cycle

Twoexperiments were conducted to determine the effects ofArtemia sp. or mysids on growth and survival ofS. officinalis hatchlings, and their effect throughout thelife cycle. For experiment I, for the first 20 days, one group was fed adultArtemia sp. and the other was fed mysid shrimp(Paramysis nouvelli). Eggs laid by females in both groupswere counted and weighed, and hatchlings were weighed, to determine differencesin both groups. For experiment II, during the first 10 days, one group was fedArtemia sp. and the other was fed mysids (P.nouveli). After the period of differentiated feeding, the 2 groupsinexperiment I were fed grass shrimp (Paleomonetes varians)to 70 days old, and dead crabs (Carcinus maenas)afterwards. Cuttlefish in experiment II were fed grass shrimp from day 10 untilthe end of the experiment. For both experiments, hatchlings fed mysids grewsignificantly bigger (p < 0.01) and survival was higher. For experiment I,eggs laid by females fed mysids and the hatchlings born from these eggs werebigger (p < 0.001) compared to the group fed Artemiasp.initially. Individual fecundity was slightly higher for females in the groupfedArtemia sp. (163 eggs female^–1) than forthe group fed mysids (144 eggs female^–1). Egg laying startedatthe age of 125 days and lasted 45 days in both groups. Time between first egglaying day and first hatchlings to be born was 21 days. The last female to die(after spawning) in both groups was 167 days (less than 6 months old).     

Aspects of the stock dynamics and exploitation of cuttlefish, Sepia officinalis (Linnaeus, 1758), in the English Channel

Basic biological parameters of cuttlefish, Sepia officinalis, in the English Channel are described from samples of commercial and research vessel landings made between April 1994 and September 1995. There was a significant difference between the length–weight relationship of male and female cuttlefish. Growth of both sexes was rapid and seasonal during the last 12 months of life. Males grew faster than females, and reached larger overall lengths and weights. Most males reached maturity before the start of their second winter, although the testis continued to develop until spawning took place the following spring. Female maturation began later and was more prolonged such that it was completed towards the end of the second winter. Adults of both sexes spawned after the second winter between late March and July. Commercial landings data showed spawning cuttlefish initially arrived on inshore grounds in the western Channel, but slightly later and in greater numbers on the inshore grounds of the middle and eastern Channel. The weight and value of cuttlefish landings made by UK vessels in the Channel increased greatly between the mid 1980s and the mid 1990s such that cuttlefish are now a major part of the earnings for several fisheries. The most important fisheries were the offshore beam trawls, and inshore otter trawls and nets. The exploitation pattern of each fishery is described from quarterly samples of commercial landings taken between April 1994 and March 1996. Each exploitation pattern is shown to be a function of the region fished, the catching gear employed, and the growth and migrations of the cuttlefish population. Some implications for stock management are discussed.     

The influence of culture density and enriched environments on the first stage culture of young cuttlefish, Sepia officinalis (Linnaeus, 1758)

The culture of Sepia officinalis hatchlings and juveniles at different densities and enriched environments was investigated. Experiments were conducted to determine effects of culture density and the use of a substrate on growth and survival. Experiment I studied the effect of three different densities (52, 515 and 1544 hatchlings m⁻²). Experiment II tested the effects of the enriched environment, using a sandy bottom with pvc shelters. Experiment III tested the effects of density on growth, survival, feeding rates and food conversions. Cuttlefish were fed live grass shrimp at rates of 20% body weight per day (BW d⁻¹). Grass shrimp (Palaemonetes varians) was supplied ad libitum as food in all experiments. In experiment I, growth was different between the three densities, with highest growth for density of 515 hatchlings m⁻². IGR was of 8.8, 9.6 and 9.2% BW d⁻¹ for the three densities tested, respectively. Both groups of experiment II had similar growth. IGR was of 10.1 and 9.7% BW d⁻¹ for enriched and non-enriched environments, respectively. Densities of 10, 45 and 120 juvenile m⁻² were used in experiment III. Significant differences in feeding rates were only found between densities of 10 and 120 cuttlefish m⁻² during the last week. Results indicate that culture of cuttlefish hatchlings could be done in a non-enriched environment, with densities not exceeding 500 hatchlings m⁻² and minimum bottom areas of about 600 cm². Densities of 120 juveniles m⁻² in a minimum area of about 1083 cm² should be considered for juveniles between 5 and 25 g. This revised version was published online in August 2006 with corrections to the Cover Date.     

急性氨氮胁迫对虎斑乌贼肝脏、鳃和脑组织结构的影响

为了探讨氨氮对虎斑乌贼器官组织结构的影响,以体质量为(13.80±0.65)g的幼虎斑乌贼为对象,研究了氨氮胁迫对其肝脏、鳃和脑组织结构的影响。根据96 h的LC50实验结果设计5个梯度(0、1、3、6和12 mg/L)进行96 h的氨氮胁迫后,利用光学显微镜和透射电子显微镜观察其肝脏、鳃和脑组织结构。结果显示,在相同浓度的氨氮胁迫下,虎斑乌贼不同组织器官之间损伤程度存在差异,其中肝脏损伤的程度最大,对氨氮胁迫表现最敏感,其次是鳃组织和脑组织,组织器官损伤程度与氨氮浓度呈现正相关。氨氮胁迫浓度越大或胁迫时间越长,肉眼观察发现肝脏颜色越鲜红,肿胀和易糜烂程度越明显,可通过肉眼观察肝脏颜色和肿胀程度初步判断机体氨中毒程度;氨氮胁迫后,对肝脏和鳃组织造成较为严重的损伤,可能是虎斑乌贼氨中毒致死的原因。当氨氮高于或等于6 mg/L时胁迫96 h后,通过显微观察发现肝小叶轮廓模糊不完整、排列不紧密和胞浆疏松透明,大量的细胞核溶解,细胞出现空泡化,肝血窦扩张;通过电镜观察发现细胞核皱缩变形、核仁消失、线粒体嵴紊乱、线粒体空泡化、线粒体外室肿胀,高尔基体数量减少;显微观察发现鳃组织的泌氯细胞和上皮细胞核溶解,细胞出现空泡化、排列紊乱,鳃丝肿胀淤血、轮廓模糊不完整,并出现坏死脱落和缺损;通过透射电镜观察,发现细胞核皱缩、核膜破损和细胞核裂解,线粒体出现了皱缩变形、空泡化和不完整破损现象;观察脑组织的神经团和视叶,未发现脑组织的细胞有显著损伤。     

金乌贼纳精囊组织结构及其精子的储存和利用

为揭示金乌贼精子进入纳精囊及产卵过程中的精子利用方式,丰富金乌贼繁殖生物学研究内容,本研究利用实验生态学和组织切片技术,检测了交配后不同时间段雌性口膜表面精子囊和纳精囊中精子数量的变化,观察分析了雌性金乌贼纳精囊的组织结构。结果显示,金乌贼纳精囊位于繁殖期雌性个体口膜腹面的突起处,共1对。纳精囊开口于口膜内表面,通过一根中央管连通整个纳精囊。中央管内壁含有大量褶皱和纤毛。在中央管两端,有12~20个储精小囊与之相连。储精小囊四周具有发达的环肌,其中储存有大量精子,并且大部分精子头部均朝向腔室内壁。完成一次交配后,雌性金乌贼对精子囊和纳精囊中精子的利用可以分为三个阶段,主要利用精子囊中的精子(交配后1~2 d);由利用精子囊中的精子向纳精囊中的精子过渡(交配后2~3 d);主要利用纳精囊中的精子(交配后3 d以上)。研究表明,从精子囊释放出的精子进入雌性口膜表面的褶皱中,通过自身运动到达纳精囊。进入纳精囊的精子通过自身运动及中央管内壁纤毛的摆动进入储精小囊,其中大部分精子头部朝向储精小囊内壁有规律地分布。在产卵过程中,雌性优先利用精子囊中的精子,而在精子囊中精子不足时,纳精囊通过肌肉收缩以及纤毛摆动将其中的精子逐渐释放出来,卵子在雌性口膜附近完成体外受精。     

Early weaning of cuttlefish (Sepia officinalis,L.) with frozen grass shrimp (Palaemonetes varians) from the first day after hatching

The suitability of early weaning cuttlefish using frozen grass shrimp, and its effects on growth and mortality was determined in a 50‐day experiment. Three food groups were used. One group (C) was fed with live prey until 25th DAH and weaned with frozen prey until the end of the experiment. In the other two groups, weaning started at the fifth DAH (W5) and first DAH (W1), also with frozen diet. Significant differences were found between C and the remaining treatments (P < 0.05) for mean wet weight (MWW), instantaneous growth rate (IGR), biomass (B) and mortality at the 25th and the 50th DAH. Despite the lower growth (~1/3 of the achieved with live food) and higher mortality (3% obtained by C versus 23% in the W1 and W5 groups), C cuttlefish presented a similar weight gain tendency to W1 and W5 groups after weaning. This is the first record of early acceptance (at the first DAH) of frozen food by cuttlefish hatchlings. These differences could be related with digestive enzymes of cuttlefish and prey, changes in nutritional composition and amount of captured prey, etc. Future research should also address the effects of this early weaning on cuttlefish life cycle.     

不同底质和温度对金乌贼仔乌饥饿耐受能力的影响

采用实验生态学方法,以金乌贼(Sepia esculenta)初孵仔乌为实验对象,研究饥饿胁迫下仔乌的行为、体征等的变化,以及不同底质(细沙组、无底质组、沙泥组)和温度条件对仔乌耐饥饿能力的影响,以期为其增殖放流最佳时期的选择和放流海域的合理规划提供参考。结果显示,饥饿对仔乌的形态特征、行为方式、活力状态等影响较大,饥饿12 d时仔乌全部死亡。水温25℃条件下,细沙组、无底质组和沙泥组的饥饿不可逆点(PNR)分别为7.5 d、8 d和9.5 d;饥饿前7 d,各组的累积死亡率相差不大,之后由高到低依次为细沙组、无底质组、沙泥组;饥饿10 d后,3个实验组仔乌的体重损失率分别为7.72%±2.80%、6.95%±2.64%和5.30%±2.41%。无底质条件下,28℃组、25℃组和22℃组的PNR时间分别为7 d、8 d和9.5 d;28℃组的死亡率显著高于其他两组(P0.05);饥饿10 d后,3组仔乌的体重损失率分别为8.90%±1.65%、6.95%±2.64%和5.79%±3.54%。实验结果表明,底质粒径较小的沙泥组对缓解仔乌饥饿起到积极影响,而粒径较大的细沙底质的作用与沙泥底质相反,随水温的升高会降低仔乌的饥饿耐受力,使其提前进入PNR。     

基于繁殖群体与补充群体结构特征的金乌贼资源增殖策略优化

利用青岛近岸海域连续监测数据,分析金乌贼繁殖群体及补充群体结构特征,比较不同洄游时期繁殖亲体的绝对生殖力与卵子规格,以及补充群体的扩散迁移过程,为金乌贼繁殖亲体筛选、增殖模式优化及放流海域合理规划等提供参考。结果显示,5—7月陆续洄游至青岛近岸的金乌贼繁殖亲体的胴长、体质量及其怀卵量随采样时间推移均呈逐渐下降趋势,前期繁殖亲体成熟卵细胞的卵径和卵重显著高于中期和后期亲体。金乌贼产黏性卵,通常将受精卵黏附于海藻或其他附着物上,其幼体生长迅速。受繁殖亲体结群期长及分批产卵等繁殖习性影响,补充群体的胴长、体质量离散水平亦随秋季采样时间推移不断升高。补充群体规格的离散可促进空间生态位分化,增加营养生态位宽幅,该生殖策略有利于减小种内摄食压力。基于金乌贼繁殖生态学特征,建议集中采集前期洄游亲体开展人工苗种繁育,以提升繁育效率,保证大规格苗种供应;依据其分批产卵习性,大规模增殖放流可分批进行,以减小种内饵料竞争,提高放流群体成活率;5—7月在近岸水深15～20 m的缓流区投放人工产卵附着基,也是一种有效的资源原位修复手段。今后应进一步探究金乌贼受精卵放流技术,优化其资源修复模式,降低增殖成本,提高资源增殖效率。