维生素E、C和HUFA交互作用对中华绒螯蟹生殖性能的影响

通过投喂添加或不添加VE、VC和HUFA的四组实验饲料,经198d饲养实验,以雌蟹的性腺系数、产卵力、孵化率、各组织超氧化物歧化酶(SOD)活性和过氧化产物丙二醛(MDA)含量等为指标,研究这两类营养素交互作用对其生殖性能的影响。结果表明,VE、VC和HUFA对雌蟹生殖性能有显著的影响(P<0.05):在产卵力方面,1组为3790个卵细胞·g-1体重,极显著高于2组(为2317个卵细胞·g-1体重)和3组(为2129个卵细胞·g-1体重)(P<0.01),显著高于4组(为3050个卵细胞·g-1体重)和5组(对照组)(为3010个卵细胞·g-1体重)(P<0.05);而孵化率方面,1组(86.17%)极显著高于2组(36.06%)、3组(29.18%)和4组(25.73%)(P<0.01),也显著高于5组(71.12%)(P<0.05)。1组和2组雌蟹性腺中SOD活性分别为40.09Nu·mL-1和39.87Nu·mL-1,相应地,MDA含量分别为6.87nmol·mL-1和3.33nmol·mL-1;而3组和4组雌蟹,尽管其性腺中SOD活性较高,分别为79.21Nu·mL-1和85.2Nu·mL-1,但由于饲料中抗氧化性VE、VC的缺乏,导致脂质过氧化发生,其MDA含量显著增加(P<0.05),分别为12.65nmol·mL-1和25.18nmol·mL-1。4组雌蟹的产卵力较大,但因VE、VC的缺乏发生脂质过氧化,导致所产的卵质低下,从而影响了卵子的孵化率。结果表明,VE、VC和HUFA都是河蟹保持良好的生殖性能的必需营     

Effects of temperature, stocking density and diet on the growth and survival of juvenile Mithraculus forceps (A. Milne Edwards, 1875) (Decapoda: Brachyura: Majidae)

Mithraculus forceps (A. Milne Edwards) has demonstrated a great potential for ornamental aquaculture and the present study tests the effects of temperature, stocking density and diet on the survival and growth of M. forceps juveniles. For 28 days post metamorphosis (DPM), the newly metamorphosed juveniles were reared at two temperatures (25±0.5 or 28±0.5°C), stocked at five densities (1, 5, 15, 30 or 60 crabs ring⁻¹; approximately 226, 1132, 3395, 6791 or 13 581 crabs m² respectively) and fed with commercial pellets (CP), microalgae (Amphora spp.), live newly hatched Artemia nauplii (NHA), frozen Artemia nauplii (FNHA), or combinations of each of these diets with NHA. At the end of the temperature experiment, carapace width of the crabs cultured at 28°C was significantly larger than the crabs reared at 25°C and average intermolt period was significantly shorter. Increased stocking density had a negative effect on survivorship and growth. Survivorship at the end of the diet experiment was significantly different between the crabs not fed, fed with CP and Amphora and the crabs fed with the other diets. Between the diet treatments, the crabs fed with NHA+Amphora were significantly larger than the ones fed with NHA+FNHA, NHA, FNHA and NHA+CP, and these in turn larger than ones fed with Amphora.     

Spawning behaviour,early development and first feeding of the bluestriped angelfish [Chaetodontoplus septentrionalis (Temminck & Schlegel, 1844)] in captivity

Successful natural spawning of Chaetodontoplus septentrionalis in captivity from 19 March to 11 May, 2008 is described for the first time. A single male dominates a harem of two females, spawning with each at dusk, from 10 min before to 20 min after sunset. Each female laid an average 119 × 10³ eggs during the spawning period. Fertilized eggs were spherical, buoyant and had a diameter of 0.83 ± 0.02 mm (mean ± SD). Embryonic development lasted 15–18 h at 28.1 °C. Newly hatched larvae were 1.60 ± 0.07 mm in total length (TL) with 27 myomeres. Larvae completed yolk absorption within 3 days post hatching (ph) at 3.01 ± 0.08 mm TL. Ten days ph, the larvae had attained 3.95 ± 0.12 mm TL. Larvae were fed either 100% s‐type rotifers (Brachionus rotundiformis), 100% copepods (Microsetella sp.), a combination of the two (50%:50%) or without live feed (starved control) to determine the effect of live feed on the survival rate. The survival was significantly (P<0.001) higher in larvae fed a combination of diet than the others. These results indicate that C. septentrionalis is a potential species for captive breeding programs and the use of a combination of diet (s‐type rotifers and copepods) may be a suitable first food for the larvae.     

Effect of dietary supplementation of phospholipids and highly unsaturated fatty acids on reproductive performance and offspring quality of Chinese mitten crab, Eriocheir sinensis (H. Milne-Edwards), female broodstock

This study was conducted to determine the optimum phospholipids: highly unsaturated fatty acids (PL/HUFA) ratio in maturation diets for female Chinese mitten crab, Eriocheir sinensis broodstock. Five isolipidtic and isonitrogenous diets were formulated to contain different amounts of pork lard, fish oil and soy lecithin with resulting PL/HUFA levels (%dry weight) of 1.4/0.3 (Diet 1), 1.6/2.5 (Diet 2), 2.3/2.0 (Diet 3), 3.8/1.5 (Diet 4) and 5.1/0.8 (Diet 5). Diet 1 lacked supplemental fish oil and soy lecithin and served as the control. Each of the five formulated diets was fed to a total of 150 female crabs for a period of 7 months. All diet treatments were triplicated with 50 crabs stocked in a pond as a replicate. After 6 months, male crabs were introduced into the ponds where females were kept, mating, spawning and egg hatching (in seawater) occurred in the following month. The nutritional value of various formulated diets was assessed based on survival, gonadosomatic index (GSI), egg production per female, fecundity (eggs/g female weight) of the females fed those diets and egg and larval (newly hatched zoea I larvae) quality.Females fed Diet 1 had the lowest GSI, egg production per female and fecundity while no significant difference were found for survival, hepatosomatic index (HSI) and the percentage of female spawned among the diet treatments (P > 0.05). Although there were no significant differences in egg diameter, egg wet or dry weights among all treatments (P > 0.05), the highest and the second highest proportions of essential fatty acids (EFA), i.e. 20:5n-3 (EPA), 22:6n-3 (DHA) and HUFA were found in the eggs produced by the females fed Diet 3 and Diet 2, respectively. Statistical analysis showed that EPA, DHA and HUFA in eggs produced by females fed Diet 3 were significantly higher than those from the other treatments (P < 0.05). Meanwhile, zoea I larvae from crabs fed Diet 3 had significantly larger carapace length than those from the other four treatments (P < 0.05). The zoea I larvae from crabs fed Diet 2 and Diet 3 also showed generally better tolerance to starvation and osmotic shock.In conclusion, our results indicated that diet included levels of PL/HUFA around 1.6/2.5 or 2.3/2.0 (% dry weight) fed female E. sinensis broodstock supported increased fecundity and elevated level of HUFA in egg, which in turn resulted in improved overall quality of newly hatched larvae.     

Ichthyoplankton-based spawning dynamics of blue mackerel (Scomber australasicus) in south-eastern Australia: links to the East Australian Current

We describe findings of three ichthyoplankton surveys undertaken along south‐eastern Australia during spring (October 2002, 2003) and winter (July 2004) to examine spawning habitat and dynamics of blue mackerel (Scomber australasicus). Surveys covered ～860 nautical miles between southern Queensland (Qld; 24.6°S) and southern New South Wales (NSW; 41.7°S), and were mainly centred on the outer shelf including the shelf break. Egg identifications were verified applying mtDNA barcoding techniques. Eggs (n = 2971) and larvae (n = 727; 94% preflexion) occurred both in spring and winter, and were confined to 25.0–34.6°S. Greatest abundances (numbers per 10 m²) of eggs (1214–7390) and larvae (437–1172) occurred within 10 nm shoreward from the break in northern NSW. Quotient analyses on egg abundances revealed that spawning is closely linked to a combination of bathymetric and hydrographic factors, with the outer shelf as preferred spawning area, in waters 100–125 m deep with mean temperatures of 19–20°C. Eggs and larvae in spring occurred in waters of the East Australian Current (EAC; 20.6–22.3°C) and mixed (MIX; 18.5–19.8°C) waters, with none occurring further south in the Tasman Sea (TAS; 16.0–17.0°C). Results indicate that at least some of the south‐eastern Australian blue mackerel stock spawns during winter‐spring between southern Qld and northern NSW, and that no spawning takes place south of 34.6°S due to low temperatures (<17°C). Spawning is linked to the EAC intrusion, which also facilitates the southward transport of eggs and larvae. Since spring peak egg abundances came from where the EAC deflects offshore, eggs and larvae are possibly being advected eastwards along this deflection front. This proposition is discussed based on recent data on blue mackerel larvae found apparently entrained along the Tasman Front.     

Seasonal shift in spawning of Atlantic cod (Gadus morhua L.) by photoperiod manipulation: egg quality in relation to temperature and intensive larval rearing

Commercial intensive fry production of Atlantic cod will be dependent on production of viable eggs independent of season. This can only be done by manipulation of maturation by photoperiod, but little is known about potential effects on egg characteristics and larval viability. In two cod broodstocks, maturation was successfully advanced or delayed 6 months compared with normal spawning season (March–April) by manipulation of photoperiod. The advanced broodstock spawned both in spring and autumn the same year. In two of the spawning tanks during autumn, ambient temperature was reduced after reaching 13.7°C during the first half of the spawning period. Egg quality and viability were monitored, and several egg batches were incubated, hatched and start‐fed for examination of growth and survival. Temperatures above 9.6°C resulted in significant reductions in fertilization and normal egg development. Concurrently, fractions of dead and unfertilized eggs increased with elevated temperature. Actual relative fecundity was not affected by temperature. Egg characteristics improved when temperature was controlled and lowered below 9.6°C. Occurrence of irregular spawners suggests that handling of broodstock fish should be avoided during maturation and spawning. Cod larvae originating from eggs of the advanced or delayed broodstocks were successfully reared beyond metamorphosis. Survival was 9.0–46.6% and 29.3% in green and clear water respectively. Survival correlated with both initial and average feeding conditions, but growth rate did not correlate with either of survival and feeding conditions. Specific growth rates (8.3–13.6% day⁻¹) is comparable with other intensive rearing trials with cod, but were lower than reported from nature‐like systems.     

OPTIMAL SALINITY-TEMPERATURE COMBINATIONS FOR THE EARLY LIFE STAGES OF GILTHEAD BREAM,Sparus auratus L.

High larval mortalities during rearing of gilthead bream, Sparus auratus L., led to experiments on the influence of salinity and temperature on eggs and yolk-sac larvae. Test salinities ranged from 5 to 70 ppt for eggs and from 15 to 45 ppt for larvae; experimental temperatures were 18–20°C for eggs and 18, 23 and 26°C for larvae. Spawning conditions were 18–20°C and 33–35 ppt salinity; the yolk-sac larvae were chosen from hatches obtained under similar conditions (18°C and 35 ppt salinity). For eggs the optimum survival range was found to be 30–50 ppt at 18°C and 15–60 ppt at 23°C, while that for yolk-sac larvae was 15–25 ppt at all three temperatures. Choosing normal development (no dorsal curvature) as the decisive criterion, the optimum salinity range for egg incubation was reduced to 30–40 ppt at 18°C and to 35–45 ppt at 23°C, while that for the yolk-sac stage remained 15–25 ppt at all test temperatures. Egg incubation was most successful at salinity-temperature combinations close to those during spawning, whereas salinity had to be reduced by at least 10 ppt for yolk-sac larvae.     

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.     

Induced out-of-season spawning of the mud crab, Scylla paramamosain (Estampador) and effects of temperature on embryo development

Treated with combined bilateral eyestalk ablation and maintenance of water temperature at 22.5±1.5 °C, mud crab Scylla paramamosain females with mature ovaries were induced to produce eggs outside the natural spawning season in subtropical southern China. Newly extruded eggs from a crab were incubated in vitro at 10, 15, 20, 25, 27, 30, 35 °C, respectively, and the embryonic development was closely monitored. Abnormal cell division was observed at temperatures 10 and 35 °C. At 15 °C, development remained at the gastrula stage by day 32 post‐spawn, at which time the experiment was terminated. Hatching of in vitro incubated eggs occurred between 20 and 30 °C. An increase in incubation temperature from 20 to 25 °C reduced the incubation duration by 14 days, 2.6 times of that measured for a similar 5 °C increase from 25 to 30 °C. Embryonic development of S. paramamosain was divided into stage 0–10, and the duration of each stage was recorded for each incubation temperature. The information obtained allows accurate prediction of hatching time of female crabs incubated under variable temperatures. Larvae hatched from in vitro incubated eggs were reared to reach first juvenile crab stage and their dry weights were similar to those of larvae hatched naturally.     

Dietary fatty acid enrichment during the spawning season increases egg viability and quality in Hippocampus hippocampus

Control of the reproductive cycle is essential to achieve a successful aquaculture industry. Seahorse reared in captivity often shows eggs of poor quality and low offspring survival due to unsuitable rearing and nutritional protocols. This study aimed to evaluate the effect of dietary enrichment, added exclusively during the spawning season, on the egg quality of Hippocampus hippocampus. The effect of enriching mysis throughout the spawning season was analysed in terms of female fecundity, egg viability, egg size and fatty acid profile. The results showed that fecundity was not affected by the enrichment of the diet, but egg viability was increased when females were fed the enriched mysis (84.9 ± 4.1% compared to 62.2 ± 9.4%). Moreover, the content of several PUFA (20:4n‐6, 18:2n‐6, 22:5n‐3, 22:5n‐6, sum of n‐6) decreased throughout the spawning season, especially in the last clutch, in eggs originated from females fed non‐enriched mysis. Eggs from females fed the enriched diet maintained the fatty acid profile throughout the spawning season. In conclusion, enrichment of the diet of H. hippocampus improved egg viability and avoided a decrease in the quality of eggs by maintaining PUFA content in the last clutches of the spawning season.     

Effect of temperature on the development of eggs and the daily pattern of spawning of round herring <Emphasis Type="Italic">Etrumeus teres</Emphasis>

Effect of temperature on the development of eggs of round herring Etrumeus teres was experimentally examined to construct a temperature-dependent egg development model. Mature fish were collected in the field and their eggs were artificially fertilized onboard. The eggs were incubated at nine temperatures set between 14.0 and 25.0°C. All eggs at the lowest three temperatures, 14.0°C, 15.0°C, and 16.0°C, ceased development and died at various stages before hatching. Durations required to hatching after fertilization ranged from 38.0 h at 25.0°C to 90.0 h at 17.5°C. The temperature-dependent egg development model, i.e., egg age in hours (y _i,t ) at the ith stage and temperature t (°C), was expressed as: y _i,t  = 4.604 × exp(−0.100 × t −0.129 × i) × i ^2.593. From the application of the model to early-stage eggs collected in the field, it is concluded that round herring starts spawning immediately after sunset and almost completes spawning by midnight. The temperature-dependent egg development model and the daily pattern of spawning presented in this study are essential tools for developing the daily egg production method to estimate the spawning stock biomass.     

Spontaneous Spawning of Captive Red Snapper, Lutjanus campechanus, and Dietary Lipid Effect on Reproductive Performance

Two experiments addressed the spontaneous spawning of red snapper, Lutjanus campechanus , under controlled temperatures and photoperiods and the effect of broodstock diets supplemented with oils rich in polyunsaturated fatty acids. In Experiment 1, broodfish were fed a standard diet (ST1) and one enriched with menhaden oil (ER1) over a 355-d period. ER1-influenced egg fatty acid profile, however, did not positively influence egg production. Both diets produced highly viable eggs and larvae but results varied within treatments. In Experiment 2, broodfish were fed either a standard diet (ST2) or one supplemented with oils (ER2) rich in docosahexaenoic and arachidonic acid using a 203-d cycle. Both treatments produced eggs but fertilization rates ranged 0–10%. There was no clear influence of the diets on egg fatty acid profiles. These results indicate that red snapper can spawn spontaneously in tanks under controlled environmental conditions and produce viable eggs and larvae when fed diets based on squid, shrimp, and fish. The fatty acid composition of the diets was reflected in the eggs to some degree, but the oil enrichments did not further enhance the reproductive performance and egg quality under the conditions of this study.     

Effect of arachidonic acid levels in broodstock diet on larval and egg quality of Japanese flounder Paralichthys olivaceus

This study investigated the effect of dietary arachidonic acid (AA) in broodstock of Japanese flounder on subsequent egg and larval quality. Diets with similar proximate composition and n-3 HUFA level, but with different AA levels (0.1%, 0.6% and 1.2% of diet), were fed to the broodstock from 3 months before and during the spawning season. Spawning was observed from March to May. Total egg production over the spawning season was highest in fish fed the 0.6% AA diet and lowest in fish fed the 1.2% AA diet. All parameters measured as egg quality (percentage of buoyant eggs, hatching rate, larval survival and normality of larvae.) were highest in fish fed the 0.6% AA diet. AA content in eggs proportionally increased with the dietary AA level. EPA content of polar lipids of eggs had a negative correlation with the AA level in diets whereas the DHA content was independent of dietary AA. The results of this study indicate that a supplement of AA at 0.6 g/100 g diet improved the reproductive performance of Japanese flounder, but a higher level of AA (1.2 g/100 g diet) negatively affected both egg and larval quality due to a potential inhibitory effect on EPA bioconversion.     

Effects of Latency Periods and Injection Doses with Carp Pituitary Extract on Spawning Performance and Egg Quality of Asian Catfish,Clarias batrachus (Linn.)

ABSTRACT

An experiment was conducted to evaluate the spawning performance and egg quality of Clarias batrachus at variable latency periods (11, 14, 17, 20, and 23 h) and doses of carp pituitary extract (10, 20, 30, 40, and 50 mg/kg). The fish could not be stripped at 11 h latency with 10 or 20 mg carp pituitary extract (CPE). The highest quantity of eggs was obtained at 14 to 23 h latency with 30–40 mg CPE or 50 mg CPE with 14 to 17 h latency, which did not vary significantly (P < 0.05) at a water temperature of 27°C–28.5°C. The eggs did not fertilize and hatch when stripped at 11-h latency period. Over 80% of total eggs stripped from females injected with 30 and 40–50 mg CPE per kg body weight, and stripped at 14 to 23 h and 14- to 17-h latency, respectively, were fertilized. However, the highest (P < 0.05) number of larvae was obtained from females injected with 40 mg CPE and stripped at 14 or 17 h latency periods. Therefore, this CPE dose and 17 h latency period combination was regarded as the best for obtaining the highest number of larvae during induced spawning of C. batrachus.     

The effect of temperature and conditioning interval on the spawning success of wild-caught blacklip (Haliotis rubra, Leach 1814) and greenlip (H. laevigata, Donovan 1808) abalone

Wild‐caught blacklip (Haliotis rubra, Leach 1814) and greenlip (H. laevigata, Donovan 1808) abalone fed a formulated feed were held at 16 or 18°C for different conditioning intervals ranging from 114 to 235 days and induced to spawn using ultraviolet‐irradiated seawater. They were conditioned again for a second identical period before another induction. For H. rubra, mean spawning rate of both sexes was higher in groups held at 18°C than at 16°C, as was the repeat spawning rate. Conversely, animals held at 16°C produced significantly more gametes than those at 18°C. Egg production peaked in groups held at 16°C for ≥165 days. While both mean and total sperm production of H. rubra varied significantly, both figures were always high. Unlike H. rubra, the spawning rate, repeat spawning rate and gamete production of both sexes of H. laevigata were higher when cultured at 16°C than at 18°C. Egg production peaked in groups conditioned at 16°C for ≥212 days. Both mean and total sperm production by H. laevigata were much lower than for H. rubra. This study demonstrates that year‐round hatchery production of seedstock of both species is possible providing broodstock are held under favourable environmental conditions, preferably 16°C.     

Spawning of captive Senegal sole (Solea senegalensis) under a naturally fluctuating temperature regime

Senegal sole aquaculture is at present limited due to poor reproduction of captive breeders in many facilities. Temperature seems to play an important role in controlling reproduction of Solea senegalensis, and differences in temperature regimes followed by various hatcheries are likely to be responsible for lack of success in some of them. This work describes the reproduction of captive soles, held in facilities that used water at ambient temperature, from a marshy environment where this species naturally breeds. Acclimated sole breeders were kept for two consecutive years. The main spawning period occurred from February to May, with a secondary spawning in autumn. Total yearly fecundity ranged from 1.15×10⁶ to 1.65×10⁶ eggs kg⁻¹ body weight. Of the total egg batches produced, only 5.4% corresponded to autumn spawns. The male population was found to produce sperm all year round, with a maximum proportion of 100% occurring in spring, and a minimum proportion of around 50% in summer. Females showed the more developed ovary stages from October to May, with partial regression in the summer months. During the main spawning period, eggs were produced between 46% and 69% of days.Spawning took place at temperatures from 13 to 23 °C, although higher fecundities (P<0.05) occurred between 15 and 21 °C. Within the range between 17 and 20 °C, the mean number of spawned eggs was 29,600±21,600 eggs day⁻¹ kg⁻¹. Most of the eggs (65–73%) were produced after temperature increased up to 2.5 °C within 3 days prior to spawning. Mean egg fertilization was 63.1±17% (year 2002) and 44.9±18% (year 2003), and hatching rates varied from 69.7±24% (2002) to 56.5 ±25% (2003). Weak correlations were found between either fertilization or hatching and fecundity, whereas a positive regression (P<0.05) indicated that higher hatching rates were achieved when fertilization increased. A weak, but significantly (P<0.05) positive correlation was found between egg fertilization and the spawning temperature. Present results indicate temperature is an important control factor for reproduction of S. senegalensis, and suggest it can be used to properly manage controlled captive reproduction of this species.     

Spawning Characteristics of the South African Mudcrab Scylla serrata (Forskål) in Captivity

Scylla serrata is a potential aquaculture species in Southern Africa. Information about its reproductive biology is required as a prerequisite to establishing hatchery technology. Adult female S. serrata were caught in the Umlalazi estuary on the subtropical east coast of South Africa and kept in captivity to observe and record spawning characteristics. Data collected included crab size and mass, time in captivity prior to spawning, fecundity per batch, relative fecundity, individual egg mass and size, size of zoea 1 larvae, incubation time, and hatch success rate. Of the 119 crabs kept in captivity 83% spawned in the maturation system– most within 40 d of capture. The crabs were highly fecund (mean relative fecundity per batch = 10,655 ± 4,069 eggs/g female) and the majority of the batches hatched within 288 h (12 d) at 27 C. Spawning in captivity occurred throughout the year, with a peak in late winter/early spring. This differs slightly from records of ovarian maturity stages of the crabs in the wild. A pattern of synchronous spawning was recorded where the females were observed to extrude their eggs in groups, commonly within 3 d of one another, separated by long periods of inactivity, suggesting an exogenous spawning cue. A total of 1,374,488 zoea larvae were obtained per kg of female per month. This means that if sufficient mature females can be caught from the wild, these could be used for stocking hatchery operations. The crabs were easy to maintain, mature, and spawn in captivity. This will facilitate future domestication which will eventually reduce the need for wild caught broodstock. The spawning characteristics of South African 5. serrata At in well with those observed for the genus throughout its distribution implying that ecological and fisheries management could be similar.     

Sustained, Natural Spawning of Southern Flounder Paralichthys lethostigma Under an Extended Photothermal Regime

Hormone‐induced spawning of southern flounder Paralichthys lethostigma has produced substantial numbers of viable eggs, but wide variations in fertilization and hatch rates have been reported. Recently, sustained natural spawning of southern flounder broodstock, without hormone induction, has been achieved in our laboratory. Adults (average weight = 1.12 kg; N= 25), including 6 captured as juveniles in 1993 and 19 captured as adults during September 1998, were stocked in two 4.8‐m³ controlled‐environment tanks in October 1998 and held under natural photothermal conditions until January 1999, when an artificial winter photo‐period of 10 L:14 D was initiated and then maintained through April 1999. Sex ratio was approximately 13 females:8 males:7 unknown. Natural spawning was observed in early December 1998 and increased in frequency to a peak in March 1999, before declining in late April. Water temperature ranged from 13.9 to 24.5 C during the spawning period. Natural spawnings over 142 d produced a total of 18.3 × 10⁶ eggs, with a mean fertilization rate of 28.0% (range = 0–100%), yielding 4.94 × 10⁶ fertilized eggs. The mean percentage of eggs that remained buoyant in full‐strength seawater (34 ppt) was 41.3% (0–98%), while hatching rate of buoyant eggs was 37.3% (0–99%) and survival of yolksac larvae to the first‐feeding stage was 30.2% (0–100%). Gonadal biopsies in late April identified six females from both tanks as probable spawners. A preliminary comparison suggests that natural spawning produced much larger numbers of viable eggs per female, with higher egg quality (i.e., fertilization and hatching success) than hormone‐induced spawning. In contrast to natural spawning, hormone‐induced strip‐spawning enabled timing of spawnings to be more precisely controlled. These results suggest that a combination of both natural and hormone‐induced spawning of photothermally conditioned fish will help produce the large numbers of eggs required to support commercial production.     

The effects of dietary supplements of polyunsaturated fatty acid on pearl oyster,Pinctada margaritifera L., gonad composition and reproductive output

Black‐lip pearl oyster, Pinctada margaritifera broodstock was collected from the wild. Egg production, hatching rate and larval development were compared between oysters induced to spawn within 2 days after collection in the wild (T1), oysters fed a pure microalgae diet during 24 days before spawning (T2) and oysters fed the same microalgal diet in which 10% of the algae were replaced with 2 μm polyunsaturated fatty acid (PUFA)‐rich microspheres (T3). Administration of lipid microspheres resulted in larger sized eggs, a higher percentage of D‐larvae and larger sized 48‐h‐old larvae (P<0.05). The total and neutral lipid contents of the gonad increased after oysters were fed with microalgae only or with supplementary diet. The major neutral and polar fractions of saturated fatty acid (SFA) were 16C and 18C fatty acids, and not influenced by the diet (P>0.05). The gonads of oysters fed supplementary PUFA contained more docosahexaenoic acid (DHA) and less monounsaturated fatty acids. Higher level of DHA in gonads of T3 was associated with oogenesis and embryogenesis success. The n‐3/n‐6 ratio in the neutral lipid fraction provides a good indication of the spawning condition and predicting egg size and hatching rate.     

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.