美洲黑石斑鱼(Centropristis striata)消化系统胚后发育的组织学观察

通过形态学与连续组织切片的方法,对美洲黑石斑鱼(Centropristis striata) 1-34 d仔鱼消化系统的胚后发育进行系统观察,分析描述鱼体消化道(食道、胃与肠道)以及消化腺(肝脏与胰腺)的发育过程.对1-15 d仔鱼连续取样,每次取样30尾,15 d后隔天取样,每次取样15尾.结果显示,在水温为(24±1)℃、盐度为30-32的条件下,初孵仔鱼卵黄囊体积很大,消化管为封闭的管状结构.美洲黑石斑鱼孵出3d后,口裂形成、开始摄食,肛门与外界连通,消化道逐渐分化形成食道、胃及肠道,肝脏、胆囊和胰腺也逐渐形成.7d后,卵黄囊与油球基本消失,食道、胃部以及肠道黏膜褶皱开始形成,消化道黏膜上皮细胞逐渐分化,肝脏出现脂肪颗粒,仔鱼具备了基本的摄食能力.11d时,仔鱼食道可见黏液细胞,随日龄的增加上皮组织中黏液细胞数量迅速增多,褶皱日益丰富;胃部分化形成贲门部、胃本体与幽门部,胃壁褶皱不断增多、伸长;肝脏血窦与中央静脉明显.20d时,鱼体胃腺形成,说明胃部消化、吸收蛋白质的能力增强;肠道次级黏膜褶皱出现,肠圈与褶皱更加复杂化;胰脏分布有大量酶原颗粒.32 d时,仔鱼消化道组织结构分明,自腔面向内依次为黏膜层、黏膜下层、肌层与浆膜层,消化道与消化腺结构和功能逐步完善.仔鱼3-7 d为内源性营养向外源性营养过渡期,应及时提供充足适口的生物饵料,仔鱼20 d后可以逐渐驯化投喂微型配合饲料.     

Ontogeny of the digestive tract in butter catfish Ompok bimaculatus (Bloch) larvae

The ontogeny of the digestive tract was studied histologically in butter catfish Ompok bimaculatus from hatching to 30?days post-hatching (dph). At hatching, the digestive tract of butter catfish consisted of a straight tube with a smooth lumen dorsally attached to the yolk sac. Between 1 and 2 dph, the mouth opened, oral valves were visible and canine-like teeth and taste buds were detected. During this period, intestine was differentiated into the anterior and posterior intestine, and the digestive accessory glands were also developed. Exogenous feeding started at 2?dph, and there was a 2-day mixed endogenous–exogenous feeding period. Most of the yolk sac reserves were consumed between 2 and 3 dph, and by 5?dph, the yolk sac was completely depleted and no longer visible in histological sections. Between 3 and 4 dph, several vacuoles (neutral lipids) were observed in the intestine and also in hepatocytes, indicating a functional absorption of nutrients from food. At 8 dph, differentiation of gastric glands was noticed, and by 9–11?dph, there were abundant gastric tubular glands arranged along numerous longitudinal folds. During the same period, pyloric sphincter appeared as an epithelial fold that separated the stomach from the anterior intestine. From 12 dph to the end of the study at 30?dph, no noticeable histological modifications were observed. The development of gastric glands is considered as the last major events in digestive tract development and their presence designates the end of larval period and the onset of the juvenile period. Hence, it is suggested that, butter catfish larvae have a morphologically complete digestive tract by 12?dph. These findings on the development of the digestive system in butter catfish may lead to a better understanding of the ontogeny and would be useful to improve the larval rearing techniques of this promising catfish species for freshwater aquaculture diversification.     

Changes in lipid class and fatty acid composition during development in pike (Esox lucius L) eggs and larvae

To establish the changes which occur during embryogenesis and early larval development, eggs, yolk sac larvae and swim-up larvae of pike were examined for lipid class and fatty acid composition. At a water temperature of 15.5°C, the embryonic phase was short (6 days) and characterized by a 41.3% decline in the lipid content of eggs, accompanied by large reductions in the amount of phosphatidylcholine (41.4% decrease), sterol esters and triacylglycerols (respectively a 41.2% decrease and a 58.1% decrease), but not phosphatidylethanolamine which increased markedly (35.6%). By the time of yolk sac absorption (7 to 11 days after fertilization) the larvae remained inactive and a limited utilization of lipids was observed. Yolk sac phosphatidylcholine was selectively incorporated into larval bodies while the levels of other lipid classes remained unchanged in the yolk. When the swim bladder was filled and the swimming stage was reached (11 days to 13 days af), the yolk was completely depleted and yolk phosphatidylcholine together with yolk triacylglycerols were catabolised. Yolk phosphatidylethanolamine and yolk sterol esters were partly incorporated into the body lipids. In the subsequent swim-up larval stage (13 to 15 days af), a steady decrease in lipids was observed (41.6%). Fluctuations in the levels of polyunsaturated fatty acids, monounsaturated fatty acids or saturated fatty acids examined from eggs or larvae were consistent with changes in lipid classes during pike development. During yolk sac absorption, pike incorporated yolk PUFA released on hydrolysis of phosphatidylcholine into the larval body. The results are discussed with reference to water temperature and in relation to the ontogenic and ecological context of pike development. This revised version was published online in July 2006 with corrections to the Cover Date.     

Histology of the developing digestive system and the effect of food deprivation in larval green sturgeon (Acipenser medirostris)

The histological development of the digestive tract in hatchery-reared green sturgeon (Acipenser medirostris) larvae and the effects of food deprivation on the digestive system organization were studied from hatching until 31 days post-hatching (dph). At hatching, the larval digestive system consisted of two rudiments: a large endodermal yolk sac and a primordial hind-gut. During the endogenous feeding phase, the wall of the yolk sac differentiated into the stomach (glandular and non-glandular regions) and the anterior and intermediate intestine, while the hind-gut primordium differentiated into the spiral valve and rectum. At the onset of exogenous feeding (15 dph at 16 °C), the organization and cytoarchitecture of the digestive system in green sturgeon larvae was generally similar to those of juveniles and adults. Larvae deprived of food exhibited a progressive deterioration, with subtle pathological changes observed after 5-d starvation: shrinkage of digestive epithelia, tissue degeneration, and necrosis were observed at 10–15 d of starvation (30 dph). No changes were observed in the mucous secretion of different regions of the digestive tract of food-deprived larvae. The histological analysis of the larval digestive system may be used to evaluate the nutritional condition of larval green sturgeon in their nursery habitats in spawning rivers, which are affected by dams and flow diversions.     

Dynamics of yolk sac and oil droplet utilization and behavioural aspects of swim bladder inflation in burbot, Lota lota L., larvae during the first days of life, under laboratory conditions

The study concerns investigation of early larval development of burbot, Lota lota. As part of a two-year study, the first 15 days (until the end of yolk sac resorption) of burbot larvae development under controlled conditions were examined. The aim of the study was to observe the moment of swim bladder inflation and the behavioural aspects of this process, as well as the analysis of yolk and oil droplet resorption and the beginning of exogenous nutrition. It was observed that larvae began to inflate their swim bladder on the 3rd day post-hatch. On 5 DPH, none of the larvae without an inflated bladder was able to swim up the distance separating it (10 cm) from the water surface. Since 9 DPH, 50 % of larvae started exogenous feeding, and the absence of yolk was observed on 13 DPH and oil droplet on 14 DPH, while on 15 DPH, 100 % of feeding larvae were observed. The presented results indicate that the analyzed period is critical for burbot, and it is characterized by a high mortality rate (over 60 %). Additionally, the results suggest that, under controlled conditions, the latest moment when burbot larvae should be given exogenous food is 9–10 DPH and until the moment of the swim bladder inflation, larvae should be kept in tanks with a low water depth (up to 10 cm). The data presented in this study could have a significant influence on the efficiency of larvae rearing, both for aquaculture and for restocking purposes.     

Ontogeny of the digestive tract in shi drum (Umbrina cirrosa L.) reared using the mesocosm larval rearing system

Histological changes of the digestive tract were studied in shi drum (Umbrina cirrosa) from hatching until 41 days post hatching (dph), when the fry had a mean (±S.D.) total length (TL) of 32 ± 2 mm and wet weight (WW) of 0.42 ± 0.07 g. Larvae were reared using the mesocosm technique, the most natural among commercially employed rearing methods for marine larvae. Shi drum opened their mouth at 2 dph (2.78 ± 0.09 mm TL), at which time 90% of the larvae already had an inflated swim bladder. The differentiation of the digestive tract into buccopharynx, esophagus, and anterior and posterior intestine was completed by 3 dph (2.82 ± 0.07 mm TL), 1 day after the onset of exogenous feeding. The alimentary canal started coiling and formed its first loop at 2 dph, while the pancreas and liver were differentiated at 3 dph. Yolk sac reserves lasted until 7 dph (4.3 ± 0.1 mm TL), suggesting a brief period of endogenous and exogenous feeding. The first esophageal goblet cells appeared at 7 dph containing acid mucins and at 8 dph taste buds appeared on the buccopharyngeal epithelium. The stomach was morphologically differentiated at 9 dph (5.5 ± 0.1 mm TL) when gastric glands became abundant in the cardiac region, and the first pyloric caeca appeared at 14 dph (10.1 ± 0.9 mm TL). Supranuclear eosinophilic vacuoles were observed in the posterior intestine between 3 and 11 dph (6.3 ± 0.9 mm TL). Their number decreased as the stomach differentiated, suggesting a change in the protein digestion mechanism. The results of the study suggest a rapid development of shi drum and its digestive system and underline the possibility of weaning larvae to artificial feed even earlier than the 12 dph employed in the present study.     

The ontogeny of the alimentary tract during larval development in common pandora Pagellus erythrinus L.

The ontogenesis of the alimentary tract and its associated structures (liver, pancreas, gall bladder) was studied histologically in common pandora from hatching (0 DAH, days after hatching) until day 50 (50 DAH). Larvae were obtained by natural spawning from a broodstock adapted to captivity. They were stocked in 1500 l tanks supplied with Isochrysis galbana and Tetraselmis suecica from hatching until the Artemia feeding stage, at a temperature of 18.5–20 °C. Larvae were fed Selco-enriched Brachionus plicatilis from day 3, Artemia nauplii from day 28 and formulated feed from day 35. At hatching, the digestive tract was a histologically undifferentiated straight tube lying dorsally to the yolk sac. At first feeding (3–4 DAH) both the mouth and anus had opened and the digestive tract was differentiated into four portions: buccopharynx, oesophagus, incipient stomach and intestine. The pancreas, liver and gall bladder were also differentiated at this stage. Within 2 days after the commencement of exogenous feeding, the anterior intestinal epithelium showed large vacuoles indicating the capacity for absorption of lipids, whereas supranuclear ninhydrin-Schiff (NS) positive inclusions indicating protein absorption were observed in the posterior intestinal epithelium. Both the bile and main pancreatic ducts had opened in the anterior intestine, just after the pyloric sphincter, at this stage. Intestinal coiling was apparent since 4 DAH, while mucosal folding began at 10 DAH. Scattered PAS-positive mucous cells occurred in the oral cavity and the intestine, while they were largely diffused in the oesophagus. Gastric glands and pyloric caeca appeared at 28 DAH, indicating the transition from larval to juvenile stage and the acquisition of an adult mode of digestion.     

Embryonic and larval development of serpae tetra Hyphessobrycon eques (Steindachner, 1882)

In this study, the embryonic and larval development stages of one of the most important ornamental fish serpae tetra (Hyphessobrycon eques) are described. The early life stage is documented from fertilization until the beginning of the juvenile period. The fertilized eggs (the average diameter = 938.55 ± 35.20 µm) were incubated at a water temperature of 26 ± 0.5°C. The cleavage finished in 1:10 hr (=h) and the early blastula stage occurred at 1:26 hr post fertilization (hpf). The gastrulation started at 3:05 hpf, and 50% epiboly was observed at 3:25 hpf. Segmentation stage was monitored at 7:26 hpf. Embryonic developmental stage was completed and hatching occurred 20–21 hpf. The total length (TL) of newly hatched larvae was 2.64 ± 0.21 mm. The larval development of serpae tetra was divided into four different periods: Yolk‐sac larva (1–4 DAH, TL = 2.77 ± 0.09 mm ‐ 3.85 ± 0.11 mm), preflexion larva (5–12 DAH), flexion larva (13–15 DAH, TL = 5.78 ± 0.46 mm on the 15th day) and post‐flexion larva (16–30 DAH, TL = 10.7 ± 0.27 mm on the 28th–30th days). The mouth and anus are closed at 1 DAH. The mouth and anus opened at 4 DAH. Exogenous feeding started on the 4th day. The first gulping of the swim bladder was on days 3. The larva begins to swim freely, and the yolk sac was completely consumed at 4 DAH. Histological structures of the eye and brain of new hatched larva were clearly identified at 1 day after hatching (DAH). According to histological findings, the digestive system (stomach, intestine) started to develop and the liver could be seen on the ventral side of the swim bladder at 5 DAH. No histological difference was observed between the anterior intestine and the posterior intestine at 15–16 DAH. The larval metamorphosis was completed, and the larvae transformed into juveniles at 28–30 DAH.     

Morphological development and allometric growth of yellowtail kingfish Seriola lalandi V. larvae under culture conditions

Morphological development and allometric growth patterns of Seriola lalandi larvae were assessed to characterize normal growth patterns under culture conditions. Early ontogenetic stages of yellowtail kingfish exhibited an exponential growth in terms of standard length as a function of age. Five development stages were characterized from hatching to the juvenile stage: larval stage I (0–2 days post hatch, dph) with endogenous feeding, characterized by a small yolk sac, unpigmented eyes, primordial finfold surrounding the body and a closed mouth; larval stage II (2–15 dph) characterized by mouth opening, complete pigmentation of eyes and the beginning of the exogenous feeding; subsequently, in the larval stage III (15–25 dph) the posterior tip of notochord of the larvae bended upward and the first rays appeared in fins, concomitant with a change in swimming behaviour; thereafter, larval stage IV (post‐flexion stage; 25–30 dph) began when larvae resembled in morphology to a juvenile organism; however, caudal and dorsal fins were not completely development. Lastly, the juvenile stage was reached 30 dph characterized by a morphology and fin structures similar to those of the adults. Growth and development of structures and organs associated with vital functions such as feeding, sensorial and breathing systems seemed to be more critical previous to 23 dph, which was reflected with a positive allometric growth of head and eyes during this period. The results from this study can be used as a tool‐guide to assess normal development in larval research with S. lalandi to improve existing rearing protocols in hatchery production.     

The effects of cadmium and copper on embryonic and larval development of ide Leuciscus idus L.

The effects of Cd and Cu on embryos and larvae of the ide Leuciscus idus were evaluated. The ide is an European cyprinid fish, natural populations of which tend to decrease. The ide is also used as a bioindicator organism to evaluate water quality. However, sensitivity of ide early developmental stages to heavy metal intoxication is not known. Fish were exposed to Cd or Cu (100 μg/L) during embryonic, larval or both developmental periods. Survival of the embryos, time of hatching, size and quality of newly hatched larvae were evaluated at the end of embryonic period. Correctly developed larvae from the control and Cd or Cu-exposed groups were transferred to clean water, Cd or Cu solutions (100 μg/L) immediately after hatching. Larval development was observed, and the larvae were photographed. Time of yolk sac resorption, onset of active feeding and swim bladder inflation were evaluated, and the measurements were done on body and swim bladder size. The results showed that exposure of embryos to Cd and Cu significantly reduced embryonic survival and increased frequency of body malformations and death in newly hatched larvae and delayed hatching. Exposure to Cd and Cu during larval period reduced larval survival, growth and delayed development (yolk utilization, beginning of active feeding and swim bladder inflation). Cadmium was more toxic to the ide embryos and larvae than copper. Exposures to metals during embryonic period alone caused adverse impact on larval performance even when larval development took place in clean water. However, exposure of embryos to Cu reduced toxic impact of metal on larvae in continuous Cu exposure compared to the non-preexposed fish, but no such an effect occurred in case of Cd exposure. The results show that even a short-term exposure to Cd or Cu during early development of ide may adversely affect recruitment of this species. Among the measured endpoints, quality of newly hatched larvae (frequency of body malformations and larvae dead immediately after hatching) and swim bladder size were the most sensitive to intoxication with both metals. Embryos were more sensitive to Cu intoxication than larvae, while in case of Cd, sensitivity of both stages was similar.     

Activities of digestive enzymes and histology of digestive system during larval development of devil stinger (Inimicus japonicus)

Devil stinger is a valuable demersal scorpaenid fish while the rearing of stinger larvae still relies on live prey. This study was conducted to illustrate the development of the main digestive enzymes and digestive system during larval development of this species to provide evidence for the application of artificial feeds. Enzymatic and histological assays were conducted from 1 day post hatching (dph) to 36 dph in larvae. The result showed that the selected digestive enzyme activities increased significantly after 15 dph. Specifically, the total trypsin activities increased significantly from 18 dph to 33 dph. The total pepsin and amylase activities increased significantly first and thereafter decreased significantly. The lipase activities followed the similar pattern with trypsin. With regard to the histological study, the stinger larvae open their mouth to first feeding at 3 dph and turned into totally exogenous nutritional stage at 6 dph. In addition, mucous membrane, rich in goblet cells, was widely distributed in oesophagus epithelium at 18 dph. The height and amounts of gastric gland in cardia and main body of the stomach increased gradually with the development of stinger larvae after 15 dph. The intestine length of stinger larvae was short, and goblet cell was abundant in anterior intestine after 12 dph, not the posterior intestine. The ontogeny of liver and pancreas started from newly hatched stage, and the differentiation of liver was prior to pancreas. The above findings would provide evidence for the use of artificial feeds from the larval stage of stinger larvae (at least from 21 dph).     

Ontogeny and distribution of alkaline and acid phosphatases in the digestive system of California halibut larvae (Paralichthys californicus)

Studies aimed to assess the digestive physiology of marine fish larvae under culture conditions are important to further understand the functional characteristics and digestive capacities of the developing larvae. Most studies to date concentrate on intestinal lumen digestion and little attention to the absorption process. Thus, the objectives of this study were to histochemically detect and quantify some of the enzymes responsible for absorption and intracellular digestion of nutrients in the anterior and posterior intestine of California halibut larvae. Alkaline and acid phosphatases were detected from the first days post-hatch (dph). Alkaline phosphatase maintained a high level of activity during the first 20 dph in both intestinal regions. Thereafter, a clear intestinal regionalization of the activity was observed with the highest levels occurring in the anterior intestine. Acid phosphatase activity gradually increased in both intestinal regions during development, and a regionalization of the activity was not observed until late in development, once the ocular migration began. Highest levels were observed in the anterior intestine at the end of metamorphosis concomitant with the stomach development. The results from this study show some morphological and physiological changes are occurring during larval development and a clear regionalization of the absorption process as the larvae develops. These ontological changes must be considered in the elaboration of diets according to the digestive capacity of the larvae.     

Ontogeny of digestive and immune system organs of larval and juvenile kelp grouper Epinephelus bruneus reared in the laboratory

ABSTRACT:   A histological examination was made of the ontogenetic development of the digestive and immune systems of the larval and juvenile kelp grouper Epinephelus bruneus reared in the laboratory. The liver, gall bladder, pancreas and the demarcating region between the intestines and rectum were formed within 3 days post-hatch (dph). During the preflexion phase (within 16 dph), revolution of the intestine concluded, and pharyngeal teeth and the mucous cells of the esophagus were differentiated. In the transitional period to the juvenile stage (25 dph), the blind sac of the stomach, gastric glands and pyloric caeca began to form. From the viewpoint of the differentiation phase of the adult-type digestive system, the kelp grouper is similar to Heterosomata, hitherto reported. The primordial thymus, kidney and spleen were present at 12, 1 and 6 dph, and the small lymphocytes in these lymphoid organs appeared at 21, 30 and 33 dph, respectively. The developmental sequence of the lymphoid organs and the appearance ages of the lymphoid organs and small lymphocytes in the lymphoid organs in the kelp grouper are similar to those of other marine fish previously reported, except for the Pacific bluefin tuna Thunnus orientalis .     

怀头鲇、鲇及其杂交F↓（1）肝、胰脏胚后发育及卵黄吸收方式

利用形态学和组织连续切片技术,对怀头鲇（Silurus soldatovi）、鲇（Silurus asotus）及其杂交F1的肝、胰脏胚后发育和卵黄吸收方式进行对比观察.结果表明,3种鲇出膜后约2天在心脏后方有一肝细胞团,3天后肝细胞团逐步增大,4天后肝分叶.以后随着各种鲇生长速度不同肝、胰脏发育程度也不同.3种鲇的胰脏均为紧凑型,卵黄囊依照先卵黄球、后脂肪的顺序被吸收,3种鲇只有怀头鲇和杂交F1代卵黄吸收方式相同.出膜后4天,各鲇的卵黄均被全部吸收,腹腔上部大部分空间为肝脏占有,同时腹腔内出现结构简单的胃及肠.研究还发现肝脏的发育与卵黄囊密切有关.[中国水产科学,2006,13（3）：460-465]     

Comparison of Two Environmental Regimes for Culture of Australian Snapper, Pagrus auratus, Larvae in Commercial-scale Tanks

The performance of Australian snapper, Pagrus auratus, larvae from 4 to 33 days posthatch (dph) under two environmental rearing regimes was evaluated in 2000‐L commercial‐scale larval rearing tanks (N = 3 tanks/treatment). The treatments were the following: (1) a varying regime of salinity (20–35 ppt), temperature (24 C), and photoperiod (12 light [L] : 12 dark [D] to swim bladder inflation and then 18L : 06D) and (2) a constant regime of salinity (35 ppt), temperature (21 C), and photoperiod (14L : 10D). The final total length (TL) and wet and dry weights (mean ± SEM) of larvae grown in the varying regime were greater (15.6 ± 0.5 mm; 42.4 ± 3.4 mg wet weight; and 7.3 ± 0.6 mg dry weight) than those of larvae grown in the constant regime (11.1 ± 0.2 mm; 12.9 ± 0.8 mg wet weight; and 2.1 ± 0.2 mg dry weight). By 33 dph, larvae in the varying regime were fully weaned from live feeds to a formulated pellet diet and were suitable for transfer from the hatchery to a nursery facility. In contrast, larvae in the constant regime were not weaned onto a pellet diet and still required live feeds. Neither survival (Treatment 1, 14.2 ± 3.0% and Treatment 2, 13.3 ± 1.9%) nor swim bladder inflation (Treatment 1, 70.0 ± 17.3% and Treatment 2, 70.0 ± 11.5%, by 13 dph) was affected by rearing regime. The incidence of urinary calculi at 7 dph was greatest initially in the varying regime; however, by 19 dph, when larvae were 8.0 ± 0.28 mm TL, very few larvae in this treatment had urinary calculi. In contrast, many larvae in the constant regime had developed urinary calculi and this continued until the end of the experiment. The incidence of urinary calculi was not associated with larval mortality. Extrapolation of the snapper larval growth curves for the constant larval rearing regime predicts that a further 15–18 d, or approximately 1.5 times longer, will be required until these larvae attain the same size and development of larvae reared in the varying regime.     

太平洋鳕(Gadus macrocephalus)亲鱼驯化培育与早期发育特征

采捕山东威海外海黄海海域的太平洋鳕(Gadus macrocephalus)亲鱼进行驯化和培育,在人工条件下成功驯化存活野生亲鱼49尾,经短期促熟培育后,通过人工授精方式获得了多批次受精卵.对胚胎和早期仔鱼发育过程进行了观察,详细描述了从受精卵到早期仔鱼各发育时期的形态特征.结果显示,太平洋鳕成熟卵子为沉性卵,圆球形,卵径为0.9-1.1 mm,无油球.胚胎发育分为5个时期,分别为卵裂期、囊胚期、原肠胚期、神经胚期和器官形成期.在水温为9-10℃、盐度为27-29的海水中孵化,受精卵历时312 h 30 min孵化出膜.初孵仔鱼全长为(3.85±0.12) mm,6日龄仔鱼开口,肛门与外界相通,进入混合营养期.8日龄仔鱼卵黄囊消耗殆尽,开始进入外源性营养阶段.仔鱼开口饵料为轮虫(Rotifer),12日龄开始摄食卤虫(Artemia saline)无节幼体.6日龄仔鱼鳔原基形成,16日龄鳔充气成为亮泡状.12日龄仔鱼形成肠道第1个生理弯曲,22日龄仔鱼第2个肠道生理弯曲形成.研究结果可为太平洋鳕亲鱼驯化培育和苗种培育提供基础资料.     

江鳕胚后形态发育特征

在直径2m的圆形玻璃钢槽内,水深0.3m,弱光,水温6～16℃下,详细观察了江鳕（Lota lota Linnaeus）胚后发育过程。结果表明,依形态发育,将出膜后的江鳕发育分为两个阶段（仔鱼期和稚鱼期）11个发育期。仔鱼期分为卵黄囊期仔鱼和后期仔鱼,历时62d;卵黄囊期仔鱼由单独依靠内源营养至混合营养过程,包括孵出期、胸鳍形成期、鳃弧期、鳔形成期和腹鳍形成期,历时31d;后期仔鱼从卵黄囊和油球消失,仔鱼完全依靠外源营养到各鳍基本形成为止,包括卵黄消失期、尾鳍形成期、背鳍分化期和臀鳍形成期,历时31d。稚鱼期包括鳞片出现期和鳞片形成期,历时5d。卵黄囊期仔鱼生长发育缓慢,后期仔鱼期和稚鱼期生长发育较快。     

Effect of water surface condition on survival,growth and swim bladder inflation of yellowfin tuna,Thunnus albacares (Temminck and Schlegel), larvae

Early‐stage mortality due to surface water tension‐related death and due to sinking to the tank bottom was investigated for yellowfin tuna, Thunnus albacares (YFT), larvae. Different aeration rates and rearing water surface conditions were examined to evaluate the effect on larval survival, swim bladder inflation and growth. The percentage survival of yolk sac larvae was significantly higher when the rearing water surface was covered with fish oil at aeration rates of 0 and 50 mL min^?1. The highest mortality occurred at the highest aeration rate of 250 mL min^?1 regardless of surface water condition. A second experiment was conducted twice under different water surface conditions: the water surface was covered by fish oil (FO), skimmed of fish oil (SS), and was not treated (NC). The percentage survival was not significantly different between treatments after 7 days of feeding. In contrast to the survival, the proportion of larvae with inflated swim bladders was significantly higher for the NC and SS groups than that of the FO group. Results of these experiments indicate that the addition of oil to the rearing water surface without its removal interferes with the initial swim bladder inflation in YFT larvae. These results also indicate that YFT larvae need to obtain (gulp) air at the water surface for initial swim bladder inflation, and success of initial swim bladder inflation may be crucial for their survival.     

The influence of salinity on the morphological development of yolk sac larvae of Atlantic halibut, Hippoglossus hippoglossus (L.)

The effects of incubation salinity on survival and morphological development of yolk sac larvae of Atlantic halibut, Hippoglossus hippoglossus (L.), were studied at two salinities, 35.5%o and 32.3%o. Yolk sac larvae incubated at 35.5%o developed early tail deformities before 50 day-degrees (9 days post-hatch), and necrosis, oedema and calculus in the urinary bladder at about 150 day-degrees (28 days post-hatch). However, the incidence and severity of mouth deformity was not influenced by salinity. The cumulative mortality up to first feeding was 17% when the larvae were incubated at 3 5.5%o compared to 7% at 32.3%o. A broad variation between the different larval groups was noted in the extent of injuries induced by the higher salinity. Therefore, salinity must be considered as a critical environmental parameter for the yolk sac larvae of Atlantic halibut in aquaculture.