Early development and allometric growth patterns in burbot Lota lota L.

This study analyzed the morphological development and allometric growth patterns of Lota lota L. (burbot) larvae reared under controlled laboratory conditions. From hatching to day 50, twenty larvae were sampled each [between 1 and 14 days post-hatch (DPH)] or every second day (between 14 and 50 DPH) and measured under a stereoscopic microscope using analytic software. Based on the external morphology, the different stages during early development of burbot were identified: yolk sac larva 0–8 DPH [3.92–4.37 mm total length (TL)]; preflexion larva 9–26 DPH (4.57–12.06 mm TL); flexion larva (between notochord degradation and its replacement with rays) 28–34 DPH (14.00–16.34 mm TL) and postflexion larva/juvenile 36–50 DPH (18.20–29.27 mm TL). Allometric growth patterns of some parameters (e.g., total length, head length, body length, tail length, head depth, body depth, eye diameter) were modeled by a power function and described by the growth coefficient. Organogenesis and changes of body proportions in burbot larvae were more rapid and complex during the yolk sac and preflexion phase of development as larvae developed most of their sensorial, feeding, respiratory and swimming systems and after notochord flexion, when most morphological changes were related to the progressive transformation from pelagic larva to demersal larva/juvenile.     

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.     

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.     

Morphological development of post hatch larval goldlined seabream Rhabdosargus sarba (Forskål, 1775)

Ultrastructural changes in Rhabdosargus sarba larva in early life history were investigated. At hatching, the digestive system was histologically undifferentiated. The digestive tract was a straight tube attached to the dorsal end of the yolk‐sac and was not connected to either the mouth or the anus. The layer of gut epithelium at some regions of the luminal surface was straight and microvilli were not present. These straight borders were not observed at 1 day post hatching (DPH) onwards as microvilli increased in number on the luminal surface and became more regular. At 2 DPH, the digestive system was well differentiated and the separation of the mid‐ and hindgut by the intestino‐rectal valve became more advanced. At 0 DPH, the eye was spherical and the retina had a zonation with undifferentiated cells. The eye also lacked differentiated photoreceptors (PR). The retinal PRs increased in length and in number as the yolk‐sac was absorbed. By 2 DPH, the eye was fully pigmented, suggesting that the larval vision system was functional. The larvae had a pure cone retina at the onset of exogenous feeding. Morphological and functional differentiation of the digestive tract and the eye of the larvae preceded the completion of yolk and oil globule absorption. The oil globule was exhausted at 4 DPH and at 2 DPH, the yolk‐sac was completely absorbed. Food particles were observed at 3 DPH. Food particle ingestion and absorption of the yolk‐sac were observed as vision became fully functional.     

Yolk utilization and growth during the early larval life of the Silver Perch,Bidyanus bidyanus (Mitchell, 1838)

The aim of this research was to investigate the yolk sac and oil globule utilization by silver perch (Bidyanus bidyanus) larvae produced from domesticated broodfish. The larvae were kept unfed in the holding tank, sampled, and investigated by image analysis software to determine various characteristics, such as the diameters of ova, water-hardened eggs, yolk-sac, oil globules, and the total length of larvae. The research illustrated that, with the exception of oil globule diameter, all other morphometric parameters were significantly lower (P < 0.05) when compared to the larvae from the wild broodfish. The yolk sac was completely absorbed at 96 h post-hatching (hph) and the oil globule was visible until 240 hph. The larvae exhibited predatory movements and tried to catch rotifer at 4 days post hatching (dph). However, the onset of feeding took place at 5 dph, while 100% of feeding occurred at 6 dph. During the first 96 h (h), larvae grew significantly faster than the next 144 h. Larvae encountered low mortalities (<10%) during the first 96 hph, before increasing significantly in the next 24 h and no unfed larvae survived post 240 h. The results also suggested that the exogenous feed should be available at 96 hph, which is well after the yolk sac is completely depleted. In addition, although most of eggs and larval performance from domesticated broodfish were inferior compared to the wild one, it has larger oil globule that could make longer of its mixed feeding period and therefore could have better in viability.     

Promotion of initial swim bladder inflation and effect of initial inflation failure on skeletal malformation in cultured seven‐band grouper Hyporthodus septemfasciatus (Thunberg)

The effects of the removal of the oily surface film on initial swim bladder inflation and survival in cultured seven‐band grouper Hyporthodus septemfasciatus were investigated during the larval stage. Additionally, the relationship between swim bladder inflation failure and malformations in later stages was examined. To explore promotion conditions for inflation, duplicate experiments were conducted under three different water surface conditions: removal of the oily surface film (ROF group), covering the water surface with an oil film (COF group), and sealing the water surface with liquid paraffin (SLP group). Larval swim bladder inflation was first observed 14 days after hatching (DAH) in the ROF group; thereafter, swim bladder inflation rates increased to 11.1% and 38.7% until the end of the experiments. This indicates that initial swim bladder inflation occurs at the pre‐flexion stage in larval development. Conversely, bladder inflation was rarely observed in the COF or SLP groups, indicating the promotional effect of surface film removal on larval swim bladder inflation and suggesting that gulping atmospheric air is necessary for initial inflation. Although larval water surface death occurred frequently in the ROF group, no significant difference existed in any group between the survival rates at 10 DAH and at the end of the experiment. The incidence rate of spinal curvature and deformation of the centra was significantly higher in individuals without initial swim bladder inflation, and these malformations mainly occurred in the caudal vertebra. Therefore, the removal of the oily surface film promotes initial swim bladder inflation and reduces larval malformations.     

Histological study of the gastrointestinal tract in longfin yellowtail (<Emphasis Type="Italic">Seriola rivoliana</Emphasis>) larvae

This work contributes basic knowledge on larval development of Seriola rivoliana. A histological study describes the development of the digestive tract and accessory glands in S. rivoliana larvae reared under laboratory conditions at 24 °C from hatching to 30 days post-hatching (DPH). At hatching (2.6 ± 0.12 mm), larvae had an undifferentiated digestive tract with a closed straight tube and a large yolk sac with an oil globule. The liver and pancreas were observed at 1 and 2 days, and the mouth and anus opened at day 2. Enriched rotifers were visible in their digestive tract. At the beginning of the pre-flexion stage, a mixed nutritional period was observed. At day 3, exogenous feeding began; the digestive tract became differentiated into the buccopharynx, esophagus, an undifferentiated stomach, and the intestines. Zymogen granules were visible in the exocrine pancreas. At day 4, supranuclear vacuoles were present in the posterior intestine, indicating the beginning of intracellular digestion. At day 5, goblet cells were present in the esophagus and became functional at day 7 in the esophagus and intestine. The buccopharynx goblet cells developed at day 15. The presence of gastric glands and differentiation of the stomach in the fundic, cardiac, and pyloric regions during the post-flexion stage occurred at day 20. This was the onset of the juvenile period and the beginning of weaning; however, a long co-feeding phase is recommended. Pyloric caeca were observed at day 30 (13.6 ± 1.6 mm). These results provide valuable information on S. rivoliana larvae biology and digestive physiology, which should be useful to improve cultivation techniques and identify ecological features involved in ontogeny.     

Determination of periods of sensitivity to low-salinity and low-temperature conditions during the early development of cultured Japanese eel Anguilla japonica larvae with respect to the rate of morphological deformity at completion of yolk resorption

The present study analyzed the rate of occurrence of deformities at completion of yolk resorption after Japanese eel larvae were exposed to low-salinity (29 psu) or low-water-temperature (20 °C) conditions (after they had been reared under suitable conditions: 34 psu, 25 °C) at various points between 0 and 8 days post-fertilization (dpf) in order to determine the period of sensitivity of the larvae to low-salinity or low-temperature conditions. No significant differences were observed between the rate of deformed larvae obtained in the groups reared under suitable conditions and the corresponding rates in groups that were exposed to low-salinity or low-temperature conditions at 4 dpf or later, but the frequency of normal larvae showed a downward trend in experimental groups that were subjected to low-salinity or low-temperature conditions at 3 dpf or earlier. Occurrence rates of pericardial edema were significantly higher in experimental groups that were exposed to low-salinity or low-temperature conditions at 2 dpf or earlier. Therefore, it was concluded that the rearing conditions for Japanese eel larvae should be maintained at 34 psu salinity and 25 °C until at least 4 dpf in order to reduce the occurrence of larval deformity at completion of yolk resorption.     

Initial swim bladder inflation in the larvae of Tilapia mossambica (Peters) and Morone saxatilis (Walbaum)

Tilapia and striped bass larvae inflate their swim bladders on the 7th–9th and 5th–7th days after hatching, respectively. The primordial bladder of Tilapia has no pneumatic duct and larvae do not gulp atmospheric gas for the initial swim bladder inflation. Prominent columnar epithelium is characteristics of the bladder of Tilapia prior to inflation. Hypoxic conditions inhibit inflation and result in degeneration of the columnar epithelium and the irreversible malfunction of the swim bladder. The swim bladder of the striped bass has a glandular epithelium and a pneumatic duct prior to inflation. The mode of the initial inflation and functional role of the pneumatic duct remain unclear, although strong aeration and turbulent water in the rearing containers were observed to be main factors enhancing normal inflation of the larval swim bladder.     

Diel and ontogenetic body density change in Pacific bluefin tuna, Thunnus orientalis (Temminck and Schlegel), larvae

Diel and ontogenetic changes in larval body density related to swim bladder volume were investigated in Pacific bluefin tuna, Thunnus orientalis, to determine the causality of larval mortality – adhesion to the water surface and contact with the tank bottom during seedling production. The density of larvae with deflated swim bladders increased with total length and days post hatch. Diel density change was observed after day 2 post hatch; owing to daytime deflation and night‐time inflation of the swim bladder, the density was relatively higher during the daytime. Increased swim bladder volumes clearly reduced larval density during the night‐time after day 9 post hatch. However, the density of larvae with inflated swim bladders was greater than rearing water density (Δρ>0.0099). The small density difference between larvae and rearing water (Δρ=0.0022?0.0100) until day 4 post hatch may have caused larval mortality by adhesion to the water surface because larvae can be easily transported to the water surface by aeration‐driven upwelling in rearing tanks. Density increased noticeably from day 5 to day 9 post hatch. The increased density difference (Δρ=0.0065?0.0209) in larvae and rearing water possibly induced mortality by contact with the tank bottom because larvae sink particularly during the night‐time on ceasing swimming.     

Optimizing initial feeding of the Pike silverside Chirostoma estor: oil droplet depletion,point of no return,growth and fatty acid utilization in larvae fed enriched rotifers

The point of no return (PNR) and disappearance of the oil droplet were measured in Chirostoma estor larvae as a function of the time of first feeding. In a separate trial, growth and survival of larvae fed rotifers enriched with Chlorella sp., cod liver oil and corn oil were assessed. Fatty acid and lipid composition of eggs, oil droplets, egg yolk, feed and larvae were also evaluated. The PNR was found between 7 and 8 days posthatching (dph). Total oil droplet depletion occurred between 7 and 11 dph, depending on the time of first feeding. Best growth and survival were obtained in larvae fed with Chlorella‐enriched rotifers, followed by those fed cod liver oil‐enriched rotifers. In larvae fed corn oil, Chlorella and cod liver oil‐enriched rotifers, total oil droplet depletion took place on days 9, 10 and 11, respectively. There was a direct relationship between presence and duration of oil droplets and the survival of larvae under different starvation conditions. The feed source could prolong the existence of the oil droplet depending on particular dietary supply of essential fatty acids; the time of its disappearance could be a useful indicator of larval vigour and health status.     

Effects of docosahexaenoic acid on growth,survival and swim bladder inflation of larval amberjack ( Seriola dumerili, Risso)

The effect of docosahexaenoic acid (DHA) on the growth performance, survival and swim bladder inflation of larval Seriola dumerili during the rotifer feeding period was investigated in two feeding experiments. Amberjack larvae at 3 day post hatching were fed rotifers enriched with (1) freshwater C hlorella (Chlo), (2) a mixture (2:1, v/v) of Chlo and DHA‐enriched C hlorella (DHA‐Chlo), (3) DHA‐Chlo and (4) DHA‐Chlo and commercial DHA emulsion, in triplicate for 7 days. The average DHA contents of the rotifers were 0.0, 0.4, 1.0 and 1.9 mg g^?1 DM respectively. The survival rate was improved by the enrichment of rotifers with DHA‐Chlo alone, and DHA‐Chlo and emulsion. Growth and swim bladder inflation of fish fed rotifers enriched with DHA‐Chlo were significantly (P < 0.05) improved, however, with increased levels of DHA further improvement was not found. DHA content in the larval whole body proportionally increased with the DHA level in the rotifers. These results suggest that DHA enrichment of rotifers is effective to improve the growth, survival rate and swim bladder inflation of amberjack larvae. The DHA requirement of amberjack larvae is estimated to be 1.5 mg g^?1 on a dry matter basis of rotifers.     

The effect of hatching time on the bioenergetics of northern pike (<Emphasis Type="Italic">Esox lucius</Emphasis>) larvae from a single egg batch during the endogenous feeding period

Size, caloric value and chemical composition were measured separately in the progeny of two northern pike (Esox lucius) females at 3-day intervals during the endogenous feeding period from hatching to final yolk resorption. Tissue, yolk and entire larvae were analysed separately in three groups of larvae that hatched at different times (between 88 and 106 degree-days post-fertilization). An integrated approach with the Gompertz model was used to compute the yolk conversion efficiency and time to maximum tissue size in early, mid and late hatched larvae. At hatching, unresorbed yolk of early hatched larvae contained more energy (39.20 J) and more protein (0.99 mg) compared to the yolk of larvae that hatched later (38.13 J and 0.92 mg protein for late hatched larvae, p < 0.05). In contrast, a significant reduction in tissue weight (?0.7 mg DW) and protein content (?0.5 mg) was found in early hatched larvae compared to those which hatched later (p < 0.05). Between days 9 and 12 post-hatching (108 and 144 degree-days post-hatching), close to the final yolk resorption, late hatched larvae stopped growing and their tissue began to be resorbed. This tissue resorption time was delayed in early hatched larvae which presented at the end of the experiment a greater tissue weight than late hatched ones. Yolk conversion efficiency in term of energy from hatching to complete yolk resorption stage was significantly higher for early and mid hatched larvae (51 %) compared to late hatched ones (44 %) (p = 0.004). Furthermore, the time to maximum tissue size was found to be negatively related to hatching time which implies that early hatched larvae take longer time to switch from one developmental stage to the next. The maximum tissue dry weight and energy content were found to be reached at approximately the same age post-fertilization for both early hatched and late hatched larvae, suggesting that the principal steps in a fish’s lifespan are better correlated with time of fertilization than hatching time.     

Apparent Problems and Potential Solutions for Production of Fingerling Striped Bass,Morone saxatilis

Data on production of fingerling striped bass, Morone saxatilis, in 103 ponds at 17 hatcheries in 1988 were related to information on management practices and water qualities. Production was highly variable, with a median of 50,000/ha. No survival was evident in 12% of ponds; numbers harvested exceeded 250,000/ ha in 5% of ponds. Best survival resulted when larvae were stocked within 2 days after pond filling was started and at hatcheries with relatively low application rates of fertilizers during the prestocking interval. No survival was evident in ponds with pH >9.0 in the week after stocking. High pH's and probably toxic concentrations of un-ionized ammonia were related to water being in ponds for too long prior to stocking and to high applications of fertilizers. Examination of samples of larvae collected at stocking and the week after stocking documented a problem with swim bladder inflation. When larvae were stocked at D5 or D6 (Dl is day of hatch), inflation success averaged 91%: when stocked at ≥D7. inflation success averaged 60%. Measures proposed to improve production include: (1) Stock larvae prior to the critical period of swim bladder inflation(D4-D5). (2) Start filling ponds as close to stocking as is feasible (filling can be completed after stocking). (3) If the concentration of available nitrogen is low, apply no more than 300 µg/L of nitrogen in the prestocking interval. (4) Add phosphorus as needed, but avoid pH>8.5 until larvae are D14.     

Combined Effects of Diet and Salinity on European Sea Bass Larvae Dicentrarchus labrax

Effects of diet, salinity, and consumption of endogenous reserves on the growth, survival and swim bladder inflation of European sea-bass larvae were studied. Primary inflation of the swim bladder occurs in 7-day-old larvae. Inflation is synchronized with the absorption of endogenous reserves. The kinetics of the consumption of these reserves varies with the diets tested, and is the slowest at higher salinity (28.7 and 37.7‰). Best results were obtained with larvae fed on Artemia nauplii. Larvae raised at lower salinity (19.7 and 10.7‰) had the highest proportion of inflated swim bladders. Larvae raised at 28.7‰ salinity had the best survival rate, while those raised at 38.7‰ had the best growth rate. Larval mortality was associated with inappropriate functioning of the swim bladder. Larvae exposed to decreasing salinity during rearing showed very high survival rates and normal swim bladder inflation.     

Early development of the silver catfish Rhamdia quelen (Quoy & Gaimard, 1824) (Pisces:Heptapteridae) from the São Francisco River Basin, Brazil

The silver catfish, Rhamdia quelen , is endemic to North, Central and South America with high aquaculture potential and wide acceptance in the market. Breeder fish were subjected to induced reproduction through hypophysation using a crude common carp pituitary extract. Egg characteristics, oocyte surface ultrastructure and histology of larval ontogenesis until whole yolk resorption were described for the first time for this species. Oocytes and semen were obtained by manual extrusion, and fertilization was conducted using the dry method. After fertilization, eggs were kept in incubators at 24 °C. The embryonic development was monitored using a stereomicroscope every 10 min until hatching. To analyse the larval development, larvae samples were collected from incubators daily until the fifth day, fixed in Bouin's fluid and subjected to routine histological techniques. The oocyte extrusion occurred 8 h after the second hormone dose at 26 °C. The oocytes were spherical, non-adhesive and yellow, with a diameter of 1471.75±47.63 μm. Scanning electron microscopy revealed a thin jelly coat covering the zona radiata in the animal pole around the micropyle. The blastopore closure occurred within 8 h after fertilization, and the fertilization rate was 79.9±5.2% at 24 °C. Embryonic development was completed within 25 h 30 min after fertilization. The complete resorption of the yolk and the formation of the digestive system organs and the mouth opening occurred on the fifth day, indicating a need for exogenous feeding. The results of this study provide information important for improvement in R. quelen culture and management.     

Characterization of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare (Schultz), and the effect of exposure to methylene blue

Failure to inflate the swim bladder is regarded a major obstacle in the rearing of many fish species. We present a study of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare. A normal developing primordial swim bladder was first discernable at the end of the first day post-hatch (p.h.) as a cluster of epithelial cells with a central lumen, surrounded by presumably mesenchymal cells. Initial inflation occurred on the fourth day p.h. Prior to inflation the swim bladder epithelium consisted of an outer squamous and inner columnar layer. Cells of the inner layer were filled at their basal region with an amorphous material, which disappeared upon inflation. A pneumatic duct was absent, and larvae presented no need to reach the water surface for inflation, suggesting that angelfish are pure physoclists. A model for the role of the amorphous material in normal initial inflation is proposed. Abnormal swim bladders were apparent from the fourth day p.h., and methylene blue (MB) at a concentration of 5 ppm significantly increased the prevalence of SBN. Histologically, abnormal swim bladders in larvae hatched in 5 ppm MB could not be distinguished from those in fish raised under routine conditions (0.5 ppm MB). We suggest that MB may have a teratogenic effect in angelfish.     

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.     

Food ingestion,prey selectivity,feeding incidence,and performance of yellowtail kingfish Seriola lalandi larvae under constant and varying temperatures

This study tested the effects of constant and varying temperatures on newly hatched yellowtail kingfish Seriola lalandi larvae in two experiments. In Experiment I, four constant temperatures (21, 23, 25, and 27 °C) were tested under fed or unfed conditions with the fish age from the day of hatch to 24 days post hatch (DPH). Temperatures at 25 and 27 °C reduced the time of fish to reach irreversible starvation, but did not affect the percentage of fish that were able to ingest food. Fish survivals at 21 and 23 °C were significantly higher than those at 25 °C by 24 DPH, but all fish died at 27 °C by 24 DPH in the treatment with food. In Experiment II, three constant temperatures (21, 23, and 25 °C) and two varying temperatures (21–23 and 21–25 °C) were compared using fish from hatch to 28 DPH. On 4 DPH, fish ingested more rotifers, but from 6 to 9 DPH, fish ingested fewer rotifers at 25 °C than at other temperatures. On 19 and 23 DPH, fish ingested more Artemia at 25 °C than at other temperatures. At 25 °C, fish selected for Artemia nauplii earlier than at other temperatures. Fish length and survival between constant temperatures (21 and 23 °C) were not significantly different, but fish survival at the constant 21 °C or at the 21–25 °C varying temperature was significantly higher than that at the constant 23 °C or at the 21–23 °C varying temperature. This study indicates that within the range of temperature tested, the optimal temperature for the first feeding larvae is 21–23 °C after hatch and mortality is likely to occur at ≥25 °C in the first 10 DPH, but fish grew faster at 25 °C after they adapted to the increasing temperature.     

美洲鲥仔、稚、幼鱼的形态发育与生长特征

通过对美洲鲥(Alosa sapidissima)仔、稚、幼各发育期的连续取样,系统观察了仔、稚、幼各期的形态变化及生长发育特征.结果显示:在水温(20±1)℃下,初孵仔鱼全长(6.75±0.60)mm;2日龄仔鱼即开口摄食,进入混合营养期;4 日龄仔鱼卵黄囊吸收完毕进人晚期仔鱼阶段,完全依靠外源物质获取能量,主要以鳔室、脊椎形成及各鳍的分化与形成为主要标志;培育至36 d,仔鱼鳃盖后缘及脊椎骨两侧线有少量鳞片状突起,标志美洲鲥结束仔鱼期进入稚鱼期;培育至65 d,仔鱼身上鳞片基本长出,腹膜闭合,美洲鲥完成变态成为幼鱼.仔鱼培育期间,除了严格控制培育水温在(20±1)℃外,2日龄仔鱼开口后就应及时投喂轮虫类开口饵料,密度为5～10 ind/mL,这是苗种培育中不可忽视的重要环节.稚鱼期间在主食枝角类、桡足类的同时进行驯食.本实验采用特制缓沉饲料及时驯化转食再过渡到伞部摄食人工浮性膨化颗粒饲料,驯食时间为21 d,驯食是成功进行人工池塘养殖的关键所在.本研究旨在探讨提高美洲鲥早期培育过程中的成活率及成功进行池塘养殖的可行性.