Spawning induction and seed production of Eastern little tuna,Euthynnus affinis (Cantor, 1849), in the post‐ and pre‐spawning seasons by hormonal treatment in a semi‐closed recirculation system with elevated temperature

We previously established a method for spawning induction in Eastern little tuna (ELT) Euthynnus affinis (Cantor, 1849) by administering a gonadotropin‐releasing hormone analog (GnRHa) during the natural spawning season in Japan (August–October). In order to establish seed production of ELT in the off‐spawning season, we first conducted three spawning induction trials by GnRHa administration from October 2011 to January 2012 using ELT broodstock (2 years old; three females and four males) maintained in a 10‐m³ tank with a semi‐closed recirculation system and static elevated temperature. Average water temperature and daily egg production in three trials lasting 11–15 days were 27.0 ± 0.09°C and 268 173 eggs (Trial 1), 27.0 ± 0.11°C and 277 9098 eggs (Trial 2), and 25.5 ± 0.39°C and 291 113 eggs (Trial 3) respectively. Mean fertilization rate and mean hatching rate were 70.4% and 60.5% (Trial 1), 83.9% and 79.6% (Trial 2), and 62.5% and 57.4% (Trial 3) respectively. We also succeeded in producing ELT larvae in the pre‐spawning season (April–July), although the quantity and quality of larvae produced were inferior to those produced in other calendar months. In trials involving periodic GnRHa administration during the off‐spawning seasons, hatched larvae were obtained in the 10‐m³ tank after six of nine administrations in the 2011–2012 off‐spawning season and in 16 of 19 administrations in the 2012–2013 off‐spawning season. The findings of this study demonstrated that hormonal treatment and thermal control could be used to extend the spawning period in ELT, potentially allowing larval production in the post‐ and pre‐spawning seasons.     

The Scale‐up of Spotted Rose Snapper,Lutjanus guttatus,Larval Rearing at Mazatlan,Mexico

The scale‐up of spotted rose snapper, Lutjanus guttatus, larval rearing is described. Fertilized eggs (480,000) were obtained from a 1‐d harvest of a natural spawning captive broodstock acclimatized for 1 yr and 6 mo in two fiberglass tanks (18 m³). Fourteen hours after spawning, 89.6% of the collected eggs were floating, of which 96.2% were transparent with live embryos. Incubation at 25–26 C lasted 21 h, with 90.2 ± 2.1% hatching percentage of normal larvae. The percentage of viable larvae at 48 h after hatching was 79.7 ± 1.9%. Initial stocking density was 10.4 ± 1.0 larvae/L 2 days after hatching (d.p.h.). A total of 22,600 juveniles (1256 ± 170 juveniles/m³) were harvested from six 3‐m³ cylindrical fiberglass tanks. Average survival was 12.1 ± 1.1%. Final mean length and weight were 5.5 ± 0.05 cm and 2.24 ± 0.04 g, respectively. Growth expressed in total length was TL = 2.1476e^0.0543t (R² = 0.9911). Final mean biomass and condition factor were 2.8 kg/m³, 12.3% and 1.346. General length‐weight ratio was W = 0.05460 LT^2.2306.     

Reproductive performance and seasonal plasma sex steroid and metabolite levels in a captive wild broodstock of brill Scophthalmus rhombus L.

This study reports egg production by captive wild brill Scophthalmus rhombus, a potential new flatfish species for Southern Europe‐Mediterranean mariculture, as well as seasonal plasma levels of 17β–estradiol, testosterone, 11–ketotestosterone, proteins, triglycerides, glucose and lactate. A mean egg production of 102 800 eggs kg body weight⁻¹ was achieved during the 2005 spawning period (January–March), although a continuous egg supply could only be obtained from some females, which had a higher relative fecundity (261 019±10 393 eggs kg⁻¹) with 12–17 eggs batches released at a mean interval of 3.4 days. Most eggs were obtained with water temperatures ranging from 12 to 14°C, and under increasing temperatures (up to 2.9°C). Potential egg viability (70.1±2.9%), fertilization (72.2±3.4%) and hatching rates (31.9±3.9%) showed high variability, with potential viability tending to decrease as the water temperature increased (mainly between 16 and 17°C) and 0% hatching above 16.6°C. The endocrine changes that brill underwent during late gametogenesis, spawning and postspawning periods were similar to those reported in other Pleuronectiformes. This study establishes an important basis for further research on the biology and physiology of brill reproduction, directed towards the optimization of the breeding techniques used currently.     

Effect of exogenous hormones on ovulation and gonadal steroid plasma levels in starry flounder, <Emphasis Type="Italic">Platichthys stellatus</Emphasis>

The present study was designed to examine the potential for inducing ovulation in starry flounder (Platichthys stellatus) using gonadotropin-releasing hormone analog (GnRHa) and human chorionic gonadotropin (hCG) to assess whether starry flounder are differentially responsive to GnRHa and hCG. Female starry flounder were injected or implanted with different doses of hCG or GnRHa pellets to examine their ovulation-inducing potential and effects on plasma levels of testosterone (T), 17β-estradiol (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). Blood samples were collected for up to 10 or 25 days post-injection or post-implantation in two separate experiments designed to mimic the early and middle stages of spawning, respectively. Fish treated with the GnRHa pellets (100 µg) showed a significant increase in the total number of stripped eggs relative to the controls. GnRHa administration had no effect on the floating rate or fertilization rate of ovulated eggs in the both experiments, whereas hCG injection affected both of these rates. Plasma T levels were not significantly different between the exogenous hormone-treated and control fish. In contrast, the plasma E2 level was elevated in those fish treated with GnRHa, regardless of injection or implantation, and was accompanied by increased numbers of stripped eggs in both experiments. Treatment with GnRHa resulted in higher 17,20βP levels compared to the controls, and there was a positive relationship between elevated plasma 17,20βP and an increase in ovulated eggs in response to GnRHa treatment. The implantation of starry flounder with GnRHa-containing pellets was effective at inducing sustained ovulation compared to hCG treatment.     

High‐quality spontaneous spawning in greater amberjack (Seriola dumerili,Risso 1810) and its comparison with GnRHa implants or injections

Production of sufficient high‐quality eggs of greater amberjack (Seriola dumerili) still constitutes the main bottleneck for commercial production of this species. The main objective of this study was to compare the quality of spontaneous spawn of greater amberjack with those obtained by either GnRHa injection or GnRHa implant protocols. Captive amberjack broodstock were distributed in three circular tanks of 40 m³. Broodstock from Tank 1 were not hormonally induced and spawned spontaneously, whereas those of Tank 2 were intramuscularly injected with GnRHa (20 µg/kg body weight) and those of Tank 3 were given EV‐500 µg GnRHa implants. The number of eggs per spawn obtained in the broodstock without hormonal treatment was larger than in those obtained with injections or implants. Egg quality was best in broodstock with spontaneous spawn, followed by GnRHa‐injected fish and then GnRHa implants. Besides, size of larvae from control and injected broodstock was similar between them and significantly higher (p < 0.01) than those from GnRHa implant spawn. Overall, this study showed that it is possible to obtain very high‐quality spontaneous spawn in greater amberjack, providing the adequate conditions. Furthermore, GnRHa weekly injections lead to similar egg viability and hatching rates than spontaneous spawn and higher fertilization rates than GnRHa hormonal implants, which is better than in previous studies.     

Conditioning,maturation and year‐round natural spawning of orange‐spotted grouper,Epinephelus coioides (Hamilton, 1822), in recirculating aquaculture system

The present experiment was aimed at studying the conditioning, maturation and natural spawning of orange‐spotted grouper, Epinephelus coioides, in a recirculatory aquaculture system (RAS). Thirty fish (n = 30; 3.35 ± 0.05 kg) were stocked in a circular tank of 125 m³ capacity fitted with an RAS for conditioning and broodstock development. After 15 days, 15 fish were implanted with 17 α methyl testosterone and letrozole at the rate of 5 mg and 0.2 mg/kg body weight, respectively, for conversion from female to male. The gonadal development started after 1 month, and by 90th day, 63.53 ± 3.78% and 2.07 ± 0.84% of the oocytes attained a size of 400–500 μm and 500–600 μm respectively. Natural spawning commenced in the RAS from 4th month onward after stocking and spawning continued round the year. The spawning pair showed courtship behaviour with a typical vertical burst of swimming just before release of gametes. The total number of eggs spawned during 1 year was 47.23 million with spawning frequency varying form 5 to 13 times per month. The association of spawning events with new moon day (lunar cycle) weakened as time progressed. The mean monthly fertilization and hatching rates varied from 77.80 ± 3.34% to 83.70 ± 1.76% and 82.80 ± 4.21% to 88.33 ± 1.39% respectively. The study proved that RAS is an efficient system that provides a stable, controllable and conducive environment for year‐round natural breeding of orange‐spotted grouper.     

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.     

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.     

Spawning induction of pejerrey Odontesthes bonariensis in captivity using sustained‐release gonadotropin releasing hormone agonist implants

The aim of this study was to induce and synchronize spawning of pejerrey Odontesthes bonariensis (Valenciennes, 1835), using gonadotropin releasing hormone agonist (GnRHa) implants. In the first experiment, the ovarian condition was assessed by ovarian biopsies and the measurement of the genital pore width (GPW). Females having the leading clutch of oocytes with a diameter of around 800–900 μm and a GPW between 4.5 and 5.5 mm were treated with GnRHa implants. Eighty per cent of females spawned between 2 and 9 days after treatment, 12 days earlier than 20% of the fish in the control group that presented signs of spawning activity. In order to avoid any possible ovarian injury and/or stress by the catheterization procedure, in a second experiment, females were selected only by visual inspection of the abdomen and GPW measurement. As in experiment 1, 80% of females spawned between 2 and 8 days after treatment, 8 days earlier than 30% of the fish that spawned in the control group. In both experiments, fertilization and hatching success were similar between control and GnRHa‐treated groups. These results clearly demonstrated that GnRHa implantation can advance and synchronize ovulation and spawning in pejerrey without affecting egg quality.     

Spawning induction in Kutum Rutilus frisii kutum (Kamenskii, 1901) using carp pituitary extract or GnRH analogue combined with metoclopramide

Kutum Rutilus frisii kutum (Kamenskii, 1901), Cyprinidae is an endemic fish of the Caspian Sea. Iranian Fisheries Organization (Shilat) produce up to 200 million fry (1–2 g body weight (b.w.)) to restock the Caspian Sea population annually. Some of these fry are produced by spawning induction in broodfish by carp pituitary extract (CPE). The objective of this study was to assay the effectiveness of the gonadotropin releasing hormone analogue (d ‐Ala⁶, Pro⁹‐Net GnRH) alone or in combination with metoclopramide (MET), a dopamine antagonist, on the percentage of ovulated females, latency period, ovulation index and fertilization success. The following hormone treatments were tested: single injection of 2 mg kg^?1 b.w. of CPE as a positive control, GnRHa alone 20 and 40 μg kg^?1 b.w. and combination of GnRHa and MET as follows: 5 μg+2.5 mg, 10 μg+ 5 mg and 20 μg+10 mg kg^?1 b.w. Negative control group was injected with 0.7% saline. The percentage of ovulated females, ovulation index and fertilization success were 90%, 71.3±1.24%, 68.4±2.3%, respectively, in the group treated with GnRHa+MET at a dose of 20 μg+10 mg kg^?1 b.w. and were significantly higher than those in the positive control (60%, 64.5±0.23%, 69.1±4.5%) (P<0.05). However, the latency period in this group was longer than that in the positive control (P<0.05). Only 20% and 40% fish ovulated in groups that received 20 or 40 μg kg^?1 b.w. GnRHa. No fish ovulated in the negative control.     

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

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

Reproductive development, GnRHa-induced spawning and egg quality of wild meagre (Argyrosomus regius) acclimatised to captivity

The objective of the study was to acclimatise wild-caught meagre (Argyrosomus regius) to captivity to produce viable eggs for aquaculture production. Twelve meagre (3 males and 9 females, mean weight?=?20?±?7?kg) were caught and transported to a land-based facility on 26 October 2006. During, March to June 2007, all three males were spermiating and five of the nine females were in vitellogenesis with mean maximum oocyte diameter ≥550?μm. No spontaneous spawning was observed. Two hormone treatments, either a single injection of gonadotropin-releasing hormone agonist (GnRHa, 20?μg?kg(-1) for females and 10?μg?kg(-1) for males) or a slow-release implant loaded with the same GnRHa (50?μg?kg(-1) for females and 25?μg?kg(-1) for males), were used to induce spawning on three different dates on 26 March 2007, 4 May 2007 and 18 April 2008. From each spawning event, the following parameters were determined: fecundity, number of floating eggs, egg size, fertilisation and hatching success, unfed larval survival, and proximal composition and fatty acid profile of the eggs. In 2007, two females that were injected on 26 March and 4 May spawned a total of 5 times producing 9,019,300 floating eggs and a relative fecundity of 198,200 eggs?kg(-1) and two different females that were implanted on the same dates spawned 14 times producing 12,430,000 floating eggs and a relative fecundity of 276,200 eggs?kg(-1). In 2008, a pair that was implanted spawned five times producing a total of 10,211,900 floating eggs and a relative fecundity of 527,380 eggs?kg(-1). The latency period was 48-72?h. Parameters were compared between hormone treatments, date of hormone induction and parents determined by microsatellites. Percentage hatch and egg size were 70?±?0.3% and 0.99?±?0.02?mm, respectively, for GnRHa-implanted fish and were significantly higher (P?相似文献   

Induced Final Maturation and Spawning of the Marbled Grouper Epinephelus microdon Captured from Spawning Aggregations in the Republic of Palau, Micronesia

A high percentage (98.3%, N = 60) of the marbled grouper Epinephelus microdon individuals captured from spawning aggregations during July and August 1993 in the waters surrounding the island of Koror, Republic of Palau, Micronesia, were in the stage of maturity at which final maturation and spawning could be hormonally induced. The sex ratio of the captured fish was highly skewed towards males (4 male:1 female). Sexually immature females comprised the smallest size class, (<0.6 kg body weight (BW) or 33.0 cm total length (TL)), while sexually mature females were restricted to the 0.6–1.5 kg BW (33.0–46.4 cm TL) groups. Males predominated in size classes >0.6 kg BW, and individuals >1.5 kg BW (46.4 cm TL) were exclusively male. All females with oocytes that averaged ( N = 50) >400 μm in diameter were successfully induced to spawn by a two-injection protocol using human chorionic gonadotropin (HCG) at total dosages of 2,100–3,200 IU/kg fish. All males used in the spawning trials were administered a single injection of HCG at dosages of 500 or 1,000 IU/kg fish. Fecundity ranged between 7.96 × 10⁵−1.24 × 10⁶kg BW, average spawned egg diameters ranged between 769–832 μm, percent fertilization ranged between 32.6%–99.9%, and hatching percentages were >90.0%. Total fat content of eggs obtained from a pooled spawning event was 14.1 mg/100 mg dry weight. The data indicate that HCG is a suitable treatment for the induction of spawning in marbled grouper females that possess a mean oocyte diameter of 400 μm or greater.     

Hormone-induced ovulation and spawning of captive and wild broodfish of the catadromous Australian bass, Macquaria novemaculeata (Steindachner), (Percichthyidae)

Australian bass, Macquaria novemacideata (Steindachner),mature but do not spawn in fresh or brackish water ponds. Ovulation and spawning of captive (n = 158)and wild Australian bass (n = 123) was induced in the normal breeding season by single injections of human chorionic gonadotropin (hCG). Doses of 100-4000IU kg-“ hCG induced ovulation and the optimum dosage was 500 IU kg” hCG. The breeding season was from mid-May to late August for wild fish,and extended into September for captive fish. There was a tendency for mean fertilization and hatching success to decline over the breeding season. Greater fertilization and hatching success was obtained from fish which spawned naturally than from stripped fish. Fish spawned after 34,2 ± 0.4 h (mean ± SE, n = 74). Ovulating fish that failed to spawn were stripped after 40.2 ± 0.3 h (n = 76). The timing of stripping and fertilization was an important factor determining hatching success. There was no apparent difference in latency periods or the number of eggs spawned between captive and wild fish. However, the mean number of eggs obtained from naturally spawned fish was higher than for stripped fish. The techniques described in this paper will assist the largescale production of Australian bass by increasing the quality and quantity of larvae from hCG-induced spawnings.     

Reproduction of striped bass, Morone saxatilis (Walbaum), broodstock: monitoring maturation and hormonal induction of spawning

Abstract Levels of gonadal steroid hormones were quantified in an adult striped bass, Morone saxatilis (Walbaum), broodstock during their gametogenic cycle. Blood plasma concentrations of Estradiol (E₂) and testosterone in females, or 11-ketotestosterone(11-KT) and testosterone (T) in males, were used as indicators of maturation. In both sexes, hormone levels were low in summer but increased significantly by late October to intermediate levels which were then maintained until late January. They then increased again rapidly to maximum pre-spawning values attained in late February or March, and subsequently decreased during the spawning period (April and May) with an increased incidence of spent fish with low hormone levels. The changes in blood hormone concentrations coincided with annual changes in photoperiod and water temperature that may be useful landmarks for maturation in captive broodstock. Mature females were implanted with pellets containing a dose of approximately 20 μg/kg body weight of [D-Ala⁶-Pro⁹-Net]-LHRH (GnRHa) in a matrix of cholesterol (CH) and cellulose. In April, they had not yet begun final oocyte maturation (FOM) and were too immature for conventional induction of spawning by injection with human chorionic gonadotropin (hCG). In early April, females given two 95% CH (slow hormone-release) GnRHa pellets (95/95) or females given one 80% CH (fast hormone-release) GnRHa pellet and one 95% CH GnRHa pellet (80/95) spawned within 13 days treatment (n= 4) with good egg fertility (76 ± 7% of total) and hatch rates (62 ± 15% of fertile). Females given dual fast-release GnRHa pellets (80/80) or control (Sham) pellets did not spawn or show evidence of increased oocyte diameter or development. In late April, four of six females given the 80/95 GnRHa pellet combination spawned within 9 days. Three fish produced fertile eggs (54 ± 18%). one spawned overripe eggs, and the remaining two increased oocyte diameter and maturation. Three corresponding controls did not spawn, and two of these showed clear signs of atresia within 11 days. In early May, some females were undergoing early FOM and were mature enough to be spawned by hCG injection. Three were given a single 80% CH GnRHa pellet and spawned within 6 days of treatment to produce fertile eggs (44 ± 6%). Of two other females given dual 80% CH GnRHa pellets, one spawned infertile eggs and the other failed to spawn within 9 days. GnRHa implants show promise as a technique for inducing spawning of captive striped bass broodstock although the optimum hormone delivery systems, dosages and release rates should be verified for fish at specific maturational stages.     

Dietary vitamin C and E supplementation and reproduction of milkfish Chanos chanos Forsskal

Milkfish Chanos chanos Forsskal broodstock (11 years old, average body weight 5.23–5.73 kg) reared in 10‐m‐diameter by 3‐m‐deep floating net cages (31–36 fish per cage) at SEAFDEC AQD's Igang Marine Substation in Guimaras Island, central Philippines, were fed daily at 3% of total body weight formulated diets (36% protein, 7–8% lipid) supplemented with 0.1% vitamin C, 0.05% vitamin E, both vitamin C and E or no vitamin supplementation (control) for 3 years. Reproductive performance was assessed in an attempt to determine the optimum nutrition for successful spawning of milkfish. The total egg production, mean number of eggs per spawning, number of spawns and mean egg diameter were not affected by dietary vitamin C and E supplementation. However, broodstock given dietary supplementation of vitamin C alone or in combination with vitamin E had a higher percentage of spawns with higher (> 90%) percentage egg viability, hatching and cumulative survival rate than those of the control. Broodstock given dietary vitamin E supplementation alone had few spawns, which made the results difficult to analyse. The results confirm the essentiality of vitamin C supplementation in producing more spawns with good egg and larval quality. The production of an adequate volume of good quality eggs and larvae to support hatchery operation is necessary to offset the huge investment in broodstock development, as it takes at least 5 years for milkfish to attain sexual maturation and spawning.     

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.     

Larval development in European hake (Merluccius merluccius L.) reared in a semi-intensive culture system

Eggs of European hake (Merluccius merluccius L.) were stripped from fish caught at sea. Larvae were kept under semi‐intensive conditions at around 12°C. In addition, eggs were incubated in single wells at 9.2, 12.7 and 14.5°C, where hatching, development and survival were closely examined. During the larval stage, a total of 299 larvae were sampled to follow development and growth. In addition a small number of juveniles were sampled. Larvae hatched approximately 4 days after fertilization, and were 2.9 mm in total length (TL). At 6‐day post hatching (dph), the larvae were 4.1 mm (TL), the jaw apparatus was developed, and the larvae had started to feed. Most of the growth during the early larval period is restricted to the head, and there is almost no increase in length for the first 3–4 weeks post hatching. Teeth and pelvic fins appear at 25 dph. Development of unpaired fins at approximately 30 dph marks the start of the larval–juvenile transition. Weaning to formulated feed was accomplished 50 dph, when external morphology was similar to that of adult hake.     

Hormonally Induced Spawning, Embryonic Development, and Larval Rearing of the Southern Temperate Banded Morwong, Cheilodactylus spectabilis

Banded morwong (Cheilodactylus spectabilis) are of interest for marine finfish aquaculture in temperate southern Australia. To improve their ovulatory response, adult females were implanted during the autumn spawning season with slow‐release pellets containing 0–400 μg luteinizing‐hormone‐releasing hormone analogue (LHRHa)/kg body weight within 24 h of capture from the wild. Compared to the sham control group, animals treated with LHRHa produced significantly more eggs on each day after implantation for the following 7 d (91 ± 39 and 290 ± 38 mL) and a higher proportion ovulated (8/12 and 27/27). Of fish treated with LHRHa, 93% ovulated 2 d after implantation and 79% ovulated three times at 2‐d intervals, whereas control animals showed no cyclicity of ovulation and few ovulated more than once. Egg production was highest at the first ovulation after LHRHa treatment and declined at subsequent ovulations. In a second experiment investigating the range 100–400 μg LHRHa, there was no effect of dose rate on ovulation parameters, which additionally examined implantation either immediately after capture or after a 5‐d delay. Compared to immediate implantation, a delay resulted in a lower proportion of animals that could be stripped after implantation (100 and 50%, respectively) and the volume of eggs was lower (135 ± 15 and 107 ± 10 mL). The egg quality was poor following delayed implantation, resulting in no fertilization after artificial insemination compared with immediate implantation in which fertilization and hatch rates were higher for eggs collected on Day 2 after implantation (79 ± 8% and 58 ± 9%) than on Day 4 (23 ± 7% and 15 ± 6%). Thus, it is important to implant animals as soon as possible after capture to ensure optimum egg quality. Good‐quality eggs were buoyant and spherical and had a diameter of 1050 ± 25 μm with a single pigmented oil droplet of 190 ± 9 μm. When a separate large batch of eggs collected 2 d after implantation with 100 μg LHRHa was inseminated and cultured at 18 C, larvae hatched after 63 ± 2 h at a standard length of 2.6 ± 0.4 mm. Newly hatched larvae were buoyant and transparent with only a few melanophores, eyes were nonpigmented and jaws were nonfunctional. By the fourth day, jaws were functional and eyes were fully pigmented. Utilization of the endogenous yolk and oil was completed by Day 6, and swimming commenced with exogenous feeding. Larvae, initially fed lipid‐enriched rotifers followed by Artemia, reached 8.9 ± 0.7 mm length on Day 55, after which they metamorphosed to the postlarval paperfish stage of development, 22 ± 0.9 mm on Day 100, and 43 ± 1.0 mm at 6 mo of age. The results show that treatment of wild‐caught females with slow‐release pellets containing LHRHa is effective for the production of eggs for hatchery rearing.     

Effects of storage and incubation temperature on the viability of eggs, embryos and larvae in two strains of an African catfish, Heterobranchus longifilis (Siluriformes, Clariidae)

Two experiments, dealing with short‐term storage of ova and thermal conditions to optimize gamete and eggs management in hatcheries of the African catfish, Heterobranchus longifilis, were carried out. In the first experiment, ova collected by stripping from two strains of H. longifilis were stored for intervals up to 8 h at two temperature regimes: in a domestic refrigerator (3–5°C) and at ambient room temperature (20.5–22°C). In the second experiment, eggs were incubated from fertilization to hatching at different experimental temperatures (21, 25, 29, 32 and 35°C) to determine the effects of temperature on the kinetics of white egg appearance, hatching times and hatching quality. Gamete storage at warmer temperatures significantly prolonged viability irrespective of the strain used. In fact, the hatching rate for ova stored at 20.5–22 and 3–5°C for 5 h ranged between 75.2–79.3% and 6.5–9.4% respectively. Loss of viability was most noticeable after 6 h storage at ambient room temperature. Post‐storage viability significantly declined after 2 h exposure to the domestic refrigerator temperature. No hatching of normal larvae took place after 8 h post‐storage time. Results from the second experiment showed that time to maximum whitening of eggs was both strain‐ and temperature‐dependent. The time to maximum mortality of eggs was shorter in the Layo strain (LS) than in the Noun strain (NS), regardless of incubation temperature. The appearance of white eggs was shorter with increasing incubation temperatures. Hatching times decreased with increasing temperature, regardless of strain. Hatching took place from 21 to 27 h and 19 to 24 h after fertilization at temperature of 29°C, respectively, for NS and LS. The length of the hatching period was remarkably shorter for LS than NS at any tested incubation temperature, except 35°C. No hatching took place at 21°C. The highest proportion of normal larvae occurred at 25 and 29°C, respectively, for NS and LS. Hatching rate was highest at 25 and 29°C, respectively, for NS and LS. There was a significantly higher proportion of deformed larvae at 35°C regardless of the strain.