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.     

GnRHa‐induced Multiple Spawns and Volition Spawning of Captive Spotted Rose Snapper,Lutjanus guttatus,at Mazatlan,Mexico

Sexual maturation and induced spawning treatments were carried out with captive spotted rose snapper, Lutjanus guttatus. A total of 3013 × 10⁶ eggs (64.7% were floating) were produced from eight treated females in 42 spawns induced with GnRHa implants during the course of the present study. GnRHa ethylene‐vinyl acetate copolymer effective doses were 204 ± 11 µg/kg in June 2005, and 224 ± 13 µg/kg in July 2005. General fertilization was 50.9 ± 34.5% and 12–14 h after spawning, viability of floating eggs was 90.4 ± 12.4%. Mean incubation period at 29–31 C was 18–20 h, and mean hatching was 94.4 ± 8.2% (73–100%). Newly hatched larvae were 2.18 ± 0.15 mm in total length (TL). One month after the last hormone experiment, previously GnRHa‐treated and untreated fish began spawning voluntarily. Hormone‐treated breeders had higher fecundity than untreated fish, producing 72.5 million eggs versus 13.9 million eggs for the untreated fish, over the following 11 mo. Combined data of volitional spawning for total egg fertilization, viability, hatching, and larval TL were 77.7 ± 1.8%, 90.3 ± 1.3%, 87.9 ± 2%, and 2.50 ± 0.12 mm, respectively. These results can ensure the sustainability of a commercial hatchery.     

Optimal temperature and photoperiod for the spawning of blue crab,Callinectes sapidus,in captivity

Like all poikilotherms, the growth and reproduction of blue crab, Callinectes sapidus depends on temperature and season. Warmer water temperatures in the Chesapeake Bay allow for ovarian development and spawning, while colder water temperatures slow their metabolism and reproduction. The current study aimed to identify optimal environmental conditions for inducing reproduction in animals held in long‐term captivity for year round production in aquaculture through environmental manipulations. Temperature and photoperiod were the main environmental factors tested for 25 weeks: 11°C and 21°C, with the following photoperiods: 0L:24D, 8L:16D, 16L:8D and 24L:0D. At 21°C, the females increased spawning frequency, which was arrested at 11°C. Shorter light exposure at 21°C increased spawning frequency, while constant light inhibited and did not produce spawning. Constant dark (0L:24D) at 21°C produced the most (86%) spawns, but yielded poor larval quality. At 21°C with all photoperiod conditions except constant light, the first spawning took 94.8 ± 32.4 days to occur (n = 17). With females producing multiple spawns, the intervals between the first and second spawns and the second and third spawns were 37.7 ± 8.7 days (n = 6) and 31.0 ± 7.1 days (n = 2) respectively. Analysis of our data using response surface methodology (RSM) predicts the following conditions: at 15–19°C and 0–10 hr darkness for maximal survival and at 19–22°C and 0–8 hr darkness for spawning. The number of larvae produced was positively correlated with size (weight) of the female C. sapidus, suggesting the importance of female size in reproduction.     

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.     

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

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

Effects of salinity and temperature during incubation on hatching and development of lingcod Ophiodon elongatus Girard, embryos

The interactive effects of salinity and temperature on development and hatching success of lingcod, Ophiodon elongatus Girard, were studied by incubating eggs at four temperatures (6, 9, 12 and 15°C) and five salinities (15, 20, 25, 30 and 35 g L^?1). Hatch did not occur in any of the 15°C treatments. Degree days (°C days) to first hatch was not influenced by temperature or salinity, however, calendar days to first hatch differed significantly for temperature (P<0.0001, 61±1, 44±1 and 35±1 days for 6, 9 and 12°C respectively). Degree days to 50% (427.1±4.2) hatch was not significantly influenced by temperature but was by salinity (P=0.0324). Viable hatch (live with no deformities, 74.1±4.0%) was greatest at 9°C and 25 g L^?1 but not significantly different in the range of 20–30 g L^?1. Larval length (9.4±0.13 mm) was greatest at 9°C and 20–30 g L^?1. Temperature and salinity significantly influenced all categories of deformities with treatments at the upper (12°C and 35 g L^?1) and lower limits (6°C and 15 g L^?1) producing the greatest deformities. The optimal temperature and salinity for incubating Puget Sound lingcod eggs was found to be 9°C and 20–30 g L^?1.     

Multiple GnRHa injections to induce successful spawning of wild caught greater amberjack (Seriola dumerili) matured in captivity

Reliable reproduction and sufficient amounts of juveniles obtained in captivity constitute a main bottleneck for mass production of greater amberjack. The aim of the present study was to combine several aspects of broodstock management and hormonal induction, to obtain a large number of high quality spawns. Captured Seriola dumerili sub‐adults were kept for three years in 10 m³ tanks. When fish were larger than 75 cm, they were individually tagged, periodically explored to determine gonad maturation and injected with gonadotropin releasing hormone analogue from June to October. A total of 15 inductions to four males and two females produced 330 821 ± 219 519 eggs/induction and a total of 22 spawns. The number of spawns and female fecundity (2.48 millions eggs/female/spawning season) were similar to those of free wild populations and higher than those previously obtained in captivity for this species. Egg quality increased from an initial low in the first two spawns in June to give, during July to October, a mean of 96.01 ± 6.50% fertilized eggs, 92.58 ± 17.56% hatched eggs, 78.66 ± 12.60% larval survival at day 3 after. These results showed that intramuscular injections of 20 μg kg^?1 body weight GnRHa under natural temperature and photoperiod conditions in the Canary Islands produced a high induction efficiency.     

Effects of temperature on the growth of pollack (Pollachius pollachius) juveniles

Growth of juvenile pollack was assessed at five constant temperatures (9, 12, 15, 18 and 21 °C) in an 84-day trial. Duplicate groups of 75 fish (initial weight 143 ± 2 g) were held in O₂ saturated water (102–103% saturation) and fed to apparent satiation. Growth increased as temperature increased from 9 °C up to a plateau at 12–15 °C (NS differences between 12 and 15 °C) followed by a decrease from 18 °C. No growth occurred at 21 °C. For the overall period, specific growth rates were 0.52% and 0.53% day^− 1 at 12 and 15 °C compared to 0.40% day^− 1 at 18 °C. Feed intake was maximum at 15–18 °C (0.68–0.69% day^− 1) and it was significantly lower at 21 °C (0.45% day^− 1). Apparent feed conversion ratio was significantly higher at 18 °C than at 12–15 °C (1.8 compared to 1.2–1.4). There was no significant change in fish whole body composition related to temperature.At the end of the experiment, fish growth recovery following a transfer from 18 and 21 °C to 15 °C was assessed using a 50-day challenge test. Growth rate of the previous 21 °C group was the same as in the 15 °C group (NS differences) and in the previous 18 °C group it was significantly lower. The study showed that pollack have a high capacity to recover from a prolonged period of low or no growth induced by high temperatures.     

Survival and development of Atlantic salmon eggs and fry at three different temperatures

Groups of Atlantic salmon (Salmo salar) eggs were incubated at 12, 10 and 8° C. At 12° C mortality was high and fry averaged little more than half the weight of those hatched at 10 or 8° C. Development of alevins to the ‘swim-up’ stage was also abnormal at 12° C. The results suggest that 10° C is optimal for incubating Atlantic salmon eggs. For the period between hatching and swim-up, the most favourable temperature varies according to the temperature used during incubation. Mortality rate during the first 6 weeks of feeding was correlated with mortality during earlier development. Total numbers of day-degrees required by the eggs and fry to reach the eyed, hatching, and swim-up stages of development were significantly less at 12° C than at 10 or 8° C. However, total day-degrees required to reach an average weight of 0.5 or 0.6 g were almost the same regardless of temperature during hatching.     

Effects of controlling temperature and light duration on seed production in tilapia, Oreochromis spilurus (Günther)

An experiment was conducted to compare the seed production of tilapia, Oreochromis spilurus (Günther), under ambient water temperature and photoperiod, and under controlled water temperature (29.0 ± 2.0 °C), and photoperiods of 13 and 14 h day^?1. Male and female breeders with average weights of 155.4 and 78.7 g, respectively, were stocked in nine 1.04 X 1.04 X 0.40 m (L X W X H) fibreglass tanks. Each tank was stocked with two males and six females. Seed collection was carried out biweekly for 300 days. The results showed that the seed kg^?1 female day^?1, seed m^?2day^?1, total seed production per tank and spawning rates of females were highest during the 14 h day^?1 photoperiod (112.4, 77.4, 24 724 and 42.1%, respectively), followed by ambient spawning conditions (104.0, 57.9, 18 356 and 36.6%, respectively), and lowest during the 13 h day^?1 photoperiod (49.5, 36.5, 12 021 and 25.7%, respectively). Under ambient spawning conditions, peak spawning occurred in May. Monthly seed production was affected by changes in temperature and light duration. In both controlled photoperiods, the peak of seed production was observed during the first month after stocking. In all treatments, spawning declined gradually after the peak, which can be attributed to exhaustion of the breeders. The findings of this study indicate that seed production of O. spilurus in Kuwait can be extended beyond the restricted spawning season of 6-7 months by maintaining water temperature at 29.0 ± 2.0 °C and photoperiod at 14 h day^?1.     

Captive Breeding of Endangered Ompok pabda with Ovatide

The Pabdah catfish, Ompok pabda, was successfully spawned with the synthetic hormone Ovatide at two different doses (0.4 and 0.6 ml/kg of body weight of female). The latency period was 9–10 h at 0.6 ml compared to 10–12 h at 0.4 ml kg^?1 of body weight. All the females spawned successfully. Average rate of fertilization (75.5 %) and hatching (60.5%) was higher with a dose of 0.6 ml kg^?1, while lower fertilization (65.1%) and hatching rate (45%) were observed at 0.3 ml kg^?1 of body weight. Fecundity ranged from 80–130 eggs gm^?1 body weight of female. Eggs hatched between 12–14 h after spawning at a water temperature 28°–32°C. The mean egg diameter was 0.95 ± 0.15 mm.     

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.     

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.     

Combined effects of photoperiod and temperature on growth and survival of African catfish (Clarias gariepinus,Burchell 1822) larvae under laboratory conditions

ABSTRACT

The effect of photoperiod (24L:00D, 12L:12D, and 00L:24D) and temperature (22 ± 1°C and 28 ± 1°C) on performance of Clarias gariepinus larvae was tested. Larvae weighing 3.2 ± 0.24 mg were cultured in aquaria at a stocking density of 20 fish L^?1 and fed twice a day on catfish starter diet (40% CP) at 10 % BW day^?1. Highest mean weight gain (31.00 mg), SGR (7.56% day^?1), and survival (83%) were achieved at photoperiod and temperature combination of 00L:24D and 28 ± 1°C. Percent survival of larvae differed significantly (p < .05) among treatments with optimal survival of (83%) in treatment combination of 28 ± 1°C and 00L:24D, while lowest survival (40%) in treatment combination of 22 ± 1°C and 24L:00D.     

Maturation and spawning of Penaeus indicus using different ablation methods

Wild immature Penaeus indicus females (11.5 ± 3.1 g body weight) were ablated by pinching, cautery or tying of one eyestalk, and stocked with control (unablated) females and males (9.2 ± 1.5 g) in a 12-m³ maturation tank. Full ovarian maturation and spawning were attained 4 days after ablation/stocking in all treatments, with a peak at 5–6 days. Seventy-five percent of ablated and unablated females spawned during the study period. Average egg numbers from complete spawns increased with size of females for all treatments. There was no significant difference in fecundity of complete spawns from the various treatments. However, hatch rates of unablated P. indicus were significantly higher than eyestalk-pinched females but not those ablated by cautery and tying. Similarly, survival after the 15-day period was lowest among pinched females.     

Spawning and Development of Larvae and Juveniles of the Rare Blue Mauritius Angelfish,Centropyge debelius (1988), in the Hatchery

This study documents the rearing and life history stages of the rare blue Mauritius angelfish, Centropyge debelius, from spawning of eggs through sexual maturity. A C. debelius pair was maintained at our facility for 22 mo. The pair was conditioned to spawn for a 4‐mo period in the fall of 2005 and a 4‐mo period in the summer of 2006 using water temperature and photoperiod manipulation. Continuous spawning was achieved at water temperatures between 22 and 24 C and a photoperiod of long day (LD) 13.5:10.5. Over a 124‐d period, the female produced 97 spawns, 59% of which resulted in fertile eggs. The average fecundity per spawn was 237 eggs (range 13–813 eggs). Fertility of all preserved spawns averaged 19.0 ± 19.8%. Larval rearing attempts using wild caught zooplankton and Artemia nauplii resulted in a total of 10 C. debelius juveniles raised through metamorphosis with an average larval survival up through metamorphosis of 0.36%. Three resulting juveniles were raised through sexual maturity. Sexual dichromatism was first observed about 180 d posthatch. A statistical model: Y = (X× 0.32437) ? (X²× 0.00043) ? 2.004, where Y = total length (mm) and X = number of days in culture, explained 97.6% of the variation in growth (P < 0.001, R² = 0.976). The development of eggs and larvae was observed to be similar to that of other Centropyge species that have been cultured. Results of this study indicate that the artificial propagation of C. debelius is technically feasible and forms the basis for this report.     

Induced triploidy in the Pacific oyster,Crassostrea gigas: Optimal treatments with cytochalasin B depend on temperature

Triploidy was induced in Crassostrea gigas using cytochalasin B (CB) (1 mg CB/l) at three temperatures: 18, 20 and 25°C. Between 3 and 5 million eggs/l were treated with CB at 15-min intervals following fertilization.Large differences in survival to straight hinge among mass spawns were observed. These were attributed to variable quality of strip-spawned eggs and treatment with CB. The negative effect of CB treatment was most apparent during critical periods of zygotic development (e.g., fertilization, polar body formation). After 48h, larvae from control and treatment groups had equivalent survival and growth rates.Replicates yielded similar percentages of triploids with standard errors of generally 10% or less. Induction curves were calculated for each temperature; triploid maxima at 18, 20 and 25°C were 52, 76 and 90%, respectively. The highest mean percentages obtained empirically at 18, 20 and 25°C were 62, 74 and 88%, respectively. No evidence for bimodal distributions to separate meiotic I and meiotic II triploids was found. Treatments at lower temperatures delayed triploid maxima which occurred approximately 30, 45 and 50 min after fertilization at 25, 20 and 18°C, respectively. Overall, the optimal treatment for inducing triploidy in the Pacific oyster (C. gigas) appears to be 30–45 min post-fertilization at 25°C, which yielded 88±9% (SE) triploidy over four replicates.     

Ovulation and egg survival following exposure of Atlantic salmon, Salmo salar L., broodstock to different water temperatures

Abstract The timing of ovulation and survival of eggs following exposure of 2-sea-winter Atlantic salmon, Salmo salar L., to different temperature regimes during the spawning season were investigated. Water temperature was either increased from 10 to 13–14°C (warm water), decreased abruptly from 10 to 5–7°C (cold water), or gradually decreased from 10 to 8°C (ambient control) from 1 November onwards. Median ovulation time was delayed by 5 weeks in the warmwater group compared with ambient controls, with 43% of the females remaining non-ovulated at the end of the study. Only minor effects were observed on timing of ovulation in the coldwater group compared with ambient controls. Survival of eggs to the eyed stage was significantly higher in the coldwater group (92·1%), compared with both the ambient control group (84·5%) and the warmwater group (76·6%). The results indicate that high water temperature during the spawning season inhibits ovulation and has a detrimental effect on gamete quality in Atlantic salmon.     

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.     

Environmentally conditioned,year‐round volitional spawning of cobia (Rachycentron canadum) in broodstock maturation systems

Year‐round control of the spawning cycle of cobia (Rachycentron canadum) has been established by using water temperature manipulation. To compare the effectiveness of using this method to induce volitional spawning in cobia, two 80 m³ recirculating aquaculture systems (RAS) were used. Temperatures in one of the maturation tanks (‘Mat 1’) were maintained between 27 and 29°C for 12 months of the 15.5‐month study period. Temperatures in the second maturation tank (‘Mat 2’) were allowed to fluctuate naturally throughout the year and ranged from 20 to 32°C. A total of 101 spawning events occurred in the tanks between the spring of 2008 and the summer of 2009 (3 April 2008 to 17 June 2009). Of the 38 total spawning events in Mat 1, 17 of them (44.7% of all Mat 1 spawning events) occurred during the off‐season (fall and winter). The egg viability rates did not differ significantly (P > 0.05) between on‐ and off‐season spawns in Mat 1. Conversely, cobia broodstock exposed to natural water temperatures (no environmental manipulation) in Mat 2 followed the natural pattern of warm water (>26°C) dependence, limiting egg production to spring and summer seasons. This method of water temperature manipulation allows for effective control of the cobia reproductive cycle without compromising egg viability.