Preliminary studies on rearing of the gilthead seabream, Sparus aurata (L.), in brackish water ponds

The first attempt to rear the gilthead seabream, Sparus aurata, in brackish water ponds in Egypt was conducted from April 1976 to February 1977. Experimental ponds were stocked with Sparus aurata fry of about 32 mm and 1.5 g average length and weight respectively at a rate of 3000 fry per one feddan of pond water (i.e. 0.42 ha). The growth rate was recorded monthly. An average length and weight of 190 mm and 78 g respectively was attained after 8 months without supplementary feeding or fertilization of pond water. mathematical equations expressing length-weight relationship and condition factor were derived for both wild and reared fish. The higher values of condition factor obtained for the reared fish in comparison to the wild fish signify their improved condition and hence their suitability for farming in Egypt.     

Induced breeding of the South American catfish, Rhamdia sapo (C. & V.)

Pituitary suspensions from the characin, Prochilodus platensis, were injected intraperitoneally into male and female Rhamdia sapo at doses between 0.37 and 6 mg dry weight per kg of body weight. Doses from 0.75 to 6.0 mg/kg effectively induced ovulation. The latent period between injection and ovulation for females held at different temperatures (17 to 27°C) decreased with increasing temperature.Stripping of gametes from both sexes, and dry method fertilization were successful and produced viable eggs. The period between ovulation and stripping for the highest hatching rates decreased from about 9 h at 20°C, to 5 h at 24°C. No viable eggs remained in samples obtained after 15 h at 20°C, or 8 h at 24°C. Hatching percentage and the fraction of deformed fry were negatively correlated (r = ?0.75; P < 0.001).     

Egg incubation and larval rearing of navaga (Eleginus navaga Pall.), polar cod (Boreogadus saida lepechin) and arctic flounder (Liopsetta glacialis Pall.) in the laboratory

The embryonic and larval development of three White Sea cold-water fish species, rate of yolk sac absorption, age at first feeding and their survival and growth when fed different food organisms, were studied.Eggs were obtained from spawners in the Bay of Kandalaksha, White Sea, and incubated in troughs and aquaria at a mean temperature of 1.5 °C, slightly above that of the sea. The incubation period for polar cod eggs lasted 35 days, for arctic flounder, 42 days and for navaga eggs, 48 days. Emergent larvae were 5.5–6.0 mm long and began feeding at 2–4 °C, 5–6 days (navaga) and 12–14 days (polar cod) after hatching, when their yolk sac was still fairly large.They were fed day-old Artemia nauplii and zooplankton taken from the sea and consisting of Calanus and Pseudocalanus nauplii 400–600 μ in length.The period of establishing first feeding is the most critical for larvae.     

Role de la temperature et de la salinite sur le taux de survie et la morphogenese au cours du developpement embryonnaire chez les oeufs du loup de mer Dicentrarchus labrax (Linnaeus, 1758) (Pisces,Teleostei, Serranidae)

The rate of hatching, duration of embryo stages and total length of newly-hatched larvae were measured in Dicentrarchus labrax, reared in 36 different combinations of temperature and salinity. Temperature varied from 4 to 20°C and salinity from 2 to 47‰. When salinities were between 11 and 20‰, this species was able to hatch at temperatures varying from 11 to 20°C. For salinities of 29, 38 and 47‰, the temperature range over which hatching occurred extended from 8 to 20°C. The Van 't Hoff equation can be adapted to calculate the relation between the rate of embryo development and the water temperature. The Q₁₀ values vary from 2.64 minimum at a salinity of 47‰ to 3.35 maximum at 20‰. The effect of temperature is significant for the means of incubation duration (P < 0.001) and the total length of newly-hatched larvae (P < 0.001).A tridimensional model of the combined effects of temperature and salinity on hatching rate has been constructed for this species.     

Growth of juvenile halibut, Hippoglossus hippoglossus (L.), under a constant and switched temperature regime

The effect of thermal history (11°C and 14°C) on growth of juvenile halibut, Hippoglossus hippoglossus (L.) (initial mean weight 140 g, n= 254), was studied. Fish were divided into four groups, two groups remaining at constant temperature (C11, Cl4), and fish in the other groups being transferred from either 11°C to 14°C (F11:14) or from 14°C to 11°C (F14:11). Twenty fish in each tank were tagged (PIT) at the start of the experiment. The final mean weights were significantly higher in F14:11 (384 g) than in F11:14 (308 g) and C14 (317 g). Further, F14:11 had significantly higher length growth rate (SLGR) than both F11:14 and C14. No significant differences between the experimental groups within each temperature (F14.11 vs. C11, and F11:14 vs. C14) were, however, found. Growth rate (SGR) declined rapidly with increasing size (from 1.4–1.8% day^?1 to 0.4–0.8% day^?1). It is concluded that the optimal temperature for growth of juvenile halibut declines with increasing size. Thus, as halibut grow larger, the temperature should be reduced to take advantage of this change in optimal temperature for growth.     

A technique for delaying embryogenesis of vendace (Coregonus albula L.) eggs in order to synchronize mass hatching with optimal conditions for lake stocking

To improve the efficiency of stocking lakes with vendace (Coregonus albula) larvae, a technique for delaying egg hatching was developed. This synchronizes mass hatching with the development of suitable thermal conditions and food availability in the lake.Water temperatures were measured in Polish hatcheries and a mathematical model of the dependence of C. albula embryogenesis on incubation temperature was utilized to predict the possibilities of delaying egg hatching. Vendace hatching can be delayed by cooling the circulation water (to 1 or 2°C) during March and April. At the beginning of May, when lake conditions are optimal for stocking, the incubation temperature should be raised (at a rate of 1.5°C h^?1) to that of the water supply. This ensures mass hatching of strong, normally developed larvae within 2–3 days. This technique facilitates both the delay of vendace hatching at minimal cost and the production of larvae on demand for lake stocking.     

Cryoprotectant microinjection toxicity and chilling sensitivity in gilthead seabream (Sparus aurata) embryos

Cryopreservation of fish embryos requires an optimal distribution of cryoprotectants inside all embryo compartments. Traditional techniques for the incorporation of cryoprotectants (CPAs) have failed to protect all fish compartments, especially the yolk sac which has been considered the principal point of embryo chilling sensitivity. In the present study, microinjection was used to incorporate cryoprotectants into the yolk sac of gilthead seabream (Sparus aurata) embryos at tail bud stage. The effect of microinjection viability, cryoprotectant toxicity and chilling resistance was evaluated through the hatching rate. Larval survival at first feeding was also determined in microinjection viability and cryoprotectant toxicity studies. Permeabilized seabream embryos were microinjected with 2.35 nl dimethyl sulfoxide (Me₂SO), methanol (MeOH), ethylene glycol (EG) (5 M, 10 M and pure) or sucrose (10% and 15%). In a second experiment, 29.5 nl and 154.0 nl of the highest concentration of each cryoprotectant were used in the same embryo stage. To test the effect of microinjected cryoprotectants on embryo chilling resistance, 29.5 nl of pure Me₂SO or 15% sucrose was microinjected into the yolk sac of tail bud stage embryos and then at a later stage, (tail-bud-free), were exposed to 3 M Me₂SO solution at − 10 °C for 30 min. Our results showed that microinjection technique did not affect the viability of tail bud stage embryos as is shown by the high hatching and survival rates. Hatching and larval survival rate at first feeding were not affected with any of the CPAs tested, showing percentages higher than 75% and 90%, respectively, when embryos were microinjected with a smaller quantity of cryoprotectant. Sucrose was the cryoprotectant better tolerated at higher concentration and volume. Cryoprotectant concentration inside the yolk higher than 1.18 M for Me₂SO, 1.5 M for EG and 2 M for methanol decreased the hatching rate. Microinjection allowed the delivery of high concentrations of CPAs into the yolk sac without deleterious effects on the embryo, but did not provide a significant level of protection for the whole embryo against chilling injury.     

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.     

Oxytetracycline (OTC) uptake following bath treatment in gilthead sea bream (Sparus aurata)

The uptake and elimination profile of oxytetracycline (OTC) following a prolong bath treatment in gilthhead sea bream (Sparus aurata) were investigated in this study. The bath experiment was carried out using a OTC concentration of 50 μg/ml for 24 h at 17-18 °C water temperature. Plasma and muscle fish samples were analysed at 1, 3, 6 and 24 h during and at 1, 2, 3, 4 and 6 d following the bath. Detectable OTC levels were revealed only at the end of bath treatment (24 h) in examined tissues of gilthead sea bream, where drug concentration was measured to be as low as 0.096 and 0.047 μg/g or ml in muscle plus skin and plasma, respectively. The findings of the present study indicate that OTC bath treatment under this dosage schedule is unlikely to confront systemic bacterial infections.     

The effect of temperature and duration of incubation on the hatching of diapause eggs of Centropages hamatus (Lilljeborg) (Copepoda, Calanoida)

Diapause eggs of Centropages hamatus were used to investigate the effect of temperature and duration of incubation on egg hatching. Eggs were incubated for 10, 12, 14, 16, 20, 24, 28, 32, 36 and 40 h at 15°C and 14L–10D. After incubation for the designated period, eggs were transferred to 25°C and monitored periodically to determine egg hatching. Control eggs were incubated solely at 15°C and monitored for egg hatching. The greatest daily hatching success of eggs occurred within 1 or 2 days after transfer from 15°C to 25°C, while the controls required 3–4 days. The cumulative hatching success of eggs was significantly lower than the control, with the exception of eggs held for at least 36 h at 15°C before transfer to 25°C. These results indicate that overall time to hatching of diapause eggs of C. hamatus can be reduced by transferring the eggs to a higher temperature, for example, 25°C, following a minimum period of time (36 h) at reduced temperature, for example, 15°C. Exposure to 15°C for only 10 h does not appear to be sufficient to result in any subsequent hatching at higher temperature.     

The effects of photoperiod and water exchange rate on growth and survival of gilthead sea bream (Sparus aurata, Linnaeus; Sparidae) from hatching to metamorphosis in mass rearing systems

The effects of photoperiod and water exchange rate on the larvae of gilthead sea bream, Sparus aurata, from hatching to metamorphosis, 60–70 days later, were tested. Survival, growth rate and condition factor were determined with photoperiods of 12 and 24 h, and water exchange rates of 0 and 25%/day.Continuous light supported the highest mean survival (3.25%), with a maximum of 7.8% from hatching to metamorphosis. Growth rate in dry weight was best under continuous light in a water system with no exchange, up to 20 days post-hatching. Highest growth rates of larvae 40–60 days old were obtained in tanks with 25% of their water exchanged daily, along with a 12-h photoperiod. Condition factor was directly correlated with larval age. For the first 30 days after hatching, condition factor was affected by photoperiod and was highest for larvae exposed to continuous light.     

Cortisol Response of Nile Tilapia,Oreochromis niloticus (L.), to Temperature Changes

Abstract

Nile tilapia, Oreochromis niloticus (L.), is a commercially-valuable fish species with high nutritional value. As a result of the intensive aquaculture of this species, handling, transport, and environmental changes that causes stress on these fish are unavoidable. The objective of this study was to determine the effects of gradual and acute temperature changes on juvenile tilapia. No significant difference (P > 0.05) was found among serum cortisol levels in juvenile tilapia when the water temperature was gradually increased from 27°C to 32°C, or 40°C, and maintained for 1 hour, although the levels were five times pretreat-ment levels. When tilapia acclimated to 27°C were subjected to 18°, 27°, 30°, 32°, 34°, 36°, 38°, or 40°C water for 10 minutes in a water bath, followed by a recovery period of 10 minutes at 27°C in the original aquaria, no significant difference (P > 0.05) in cortisol levels was observed among treatments except for significantly elevated levels at 38°C and 40°C. When tilapia acclimated to 27°C were subjected to the same temperature exposures but given a recovery period of 60 minutes at 27°C in the original aquaria, there was no significant (P > 0.05) increase in cortisol levels in tilapia among treatments from 18° to 36°C; but there was a significant (P > 0.05) increase between values from those treatments at 38° and 40°C. Acute temperature changes initiated the cortisol response as early as 10 minutes in fish following exposure to 38°C or 40°C and resulted in significant increases in the 38°C and 40°C treatments following 1 hour of recovery at 27°C. These results have implications for the management of tilapia during bacterial challenge, vaccination, and handling and transport during aquacultural activities.     

Breeding-related growth of captive Sparus aurata (Teleostei,Perciformes)

Growth is arrested in male and female Sparus aurata during gonadal recrudescence and spawning. Growth and feeding rates of fish exposed to a constant long photoperiod ($\text{16L}\text{8D}$) were significantly higher than those of fish under a natural photoperiod. When the experimental photoperiod was shortened, fish underwent gonadal recrudescence and reduced feeding, and their growth was arrested. Fish under the long photoperiod regime reached the commercial weight of 350 g six months earlier than the controls.     

Effect of different commercial spawning agents and thermal regime on the effectiveness of pikeperch, Sander lucioperca (L.), reproduction under controlled conditions

Pikeperch, Sander lucioperca (L.), has been identified as one of the most perspective candidates for diversification of freshwater aquaculture. However, some aspects of production are still being developed, and controlled reproduction is one of the bottlenecks. The aim of the present study was to compare the effectiveness of different commercial spawning agents in the induction of final oocyte maturation (FOM) and ovulation in wild spawners. Within the study, four spawning agents [human chorionic gonadotropin (hCG), mixed human and horse gonadotropin (PG-600), carp pituitary (CPH) and mammalian GnRH analogue combined with metoclopramide (Ovopel)] in different thermal regimes (13 and 15 °C) were tested. In both thermal regimes, the highest (P < 0.05) ovulation rate among the treatment groups was obtained after stimulation with hCG (100 % in both cases). Latency time was the shortest in groups where CPH was used (2–3 and 3–4 days for 15 and 13 °C) and was similar in the remaining groups (3–4 and 4–5 days for 15 and 13 °C, respectively). Embryo survival was the highest in groups treated with hCG (78.9 and 81.3 % at hatching stage for 15 and 13 °C, respectively). Hormonal stimulation did not significantly affect spermiation rate or spermatozoa motility (P > 0.05). Based on the obtained results, hCG can be recommended for induction of FOM and ovulation in pikeperch. In addition, the thermal regime within the tested range seemed to have no effect on the reproduction outcome, and the application of lower temperature only prolonged the time of ovulation.     

Ovulation rate,latency period and ova viability after GnRH- or hCG-induced breeding in the Asian catfish Pangasius hypophthalmus(Siluriformes,Pangasiidae)

Over a 3-year period at the Sukamandi station (West Java, Indonesia), 107 Pangasius hypophthalmus females were selected on the basis of a modal oocyte diameter greater than 1.0 mm and treated with either Ovaprim (n = 97) or hCG (n = 10) to induce oocyte maturation and ovulation. The two hormonal treatments led to similar results in terms of ovulation rate (88 and 90 %), hatching rate (72 ± 25 and 82 ± 11 %) and relative fecundity (171 000 ± 73 000 and 128 000 ± 60 000 ova·kg^–1, with Ovaprim and hCG, respectively). The latency period between the last hormone injection and ovulation was negatively correlated to water temperature but showed important variations at a same temperature depending on individual females (e.g. between 5 and 11 h at 28–29 °C). The ovulation time was therefore difficult to predict accurately in this species. The assessment of the viability of ova retained in the ovarian cavity after ovulation showed that the process of overripening occurs rapidly in P. hypophthalmus. The overall quality of ova began to decline as early as 2 h after ovulation and, after 3 h, hatching rates decreased and the proportion of deformed larvae increased significantly in comparison to those observed at the time of ovulation. In some individual females this process occurred even more rapidly, with a sharp decrease in hatching rates between 1 and 2 h post-ovulation. The duration of ova survival did not appear to depend on the type of hormone treatment used to induce ovulation (Ovaprim or hCG). For optimized gamete management in hatcheries, it is therefore recommended to check carefully the females for the occurrence of ovulation (between 3 and 11 h after the last hormone injection, depending on water temperature) and to strip and fertilize the eggs less than 2 h thereafter.     

Effects of different step‐wise temperature increment regimes during egg incubation of Atlantic cod (Gadus morhua L.) on egg viability and newly hatched larval quality

We carried out an experiment to determine how rapidly the early incubation temperature of Atlantic cod eggs can be increased without affecting normal embryonic development and hatching. Atlantic cod eggs were incubated at a constant low temperature (4.5 ± 0.5°C; T5 – control) and four temperature increment treatments where the temperatures were increased stepwise from 4.5°C at zygote stage to 9.5 ± 05°C (T1‐8 h, T2‐32 h, T3‐64 h and T4‐96 h). Embryonic cell symmetry, embryonic mortality, hatching success and larval skeletal abnormalities, length and yolk sac volume were recorded. Larval samples were also taken at hatch for histological analysis. Except for higher egg mortality and lower hatching success in the T1, the differences among experimental groups were minor. Cell asymmetries and embryo mortalities were not significantly different between the control and T2–T4 treatment groups. Control larvae were significantly longer and had smaller yolk reserves at hatch than T1–T4 larvae and larvae from T2 had the largest yolk reserves. Tissue and organ histology of hatched larvae were similar. Considering embryonic cleavage pattern, hatching success and larval morphology and histology, a gradual increment of temperature in 32 h seems to be the better choice for future developmental programming studies in Atlantic cod.     

In vivo and in vitro treatments against Sparicotyle chrysophrii (Monogenea: Microcotylidae) parasitizing the gills of gilthead sea bream (Sparus aurata L.)

The effect of in vitro and in vivo treatments against Sparicotyle chrysophrii, a microcotylid parasite of gilthead sea bream (Sparus aurata L.), was studied. In vitro chemical treatments were targeted to eggs, oncomiracidia and adults, and were tested both as disinfectants and therapeutics for infected animals. The compounds were: distilled water, formalin, limoseptic ®, hydrogen peroxide, chlorine, and praziquantel (PZQ). Larvae were sensitive to all the treatments, but adults were more resistant, as chlorine (60 ppm - 1 h), hydrogen peroxide (100 ppm - 30 min) and PZQ (50 ppm - 30 min) produced only 10% mortality. All adults were killed only with distilled water, limoseptic (0.1% - 5 min), formalin (300 ppm - 30 min), or hydrogen peroxide (200 ppm - 30 min). Eggs were the most resistant stage, as only 30 min in limoseptic (0.1% in distilled water) or in formalin (300 ppm) prevented hatching. PZQ was used in vivo either as a curative or preventive treatment. The highest dose tested (400 mg kg^− 1 BW; effective dose 116.3 mg kg^− 1 BW due to palatability problems leading to 45% reduction in host food intake) did not significantly decrease prevalence of infection when given for 6 consecutive days. A lower dose (200 mg kg^− 1 BW) (effective dose 158.1 mg kg^− 1 BW) was rejected to a lower degree and decreased the prevalence of infection from 90% to 40%. When a lower dose (40 mg kg^− 1 BW) was administered for longer periods (20 days), food intake was reduced slightly, but the infection did not decrease significantly. The oral intubation with PZQ (200 mg kg^− 1 BW) once a week for 4 weeks did not prevent the infection of fish by cohabitation. However, a significant reduction in the abundance of the parasite was registered. In view of the results, recommendations for fish treatment and disinfection of aquaculture facilities are discussed.     

Early development,growth and survival of the yellow crab Cancer anthonyi Rathbun (Decapoda,Brachyura) in the laboratory

Larvae of the yellow crab, Cancer anthonyi Rathbun, were reared through five zoeal stages and one megalops stage in the laboratory. Total larval development times were 33 and 45 days at 22°C and 18°C, respectively. Survival rates to the first crab instar, for larvae reared in recirculating systems on a diet of Artemia nauplii, were 26% at 22°C and 17% at 18°C. Although no larvae reared in glass containers at 22°C survived past the first zoeal stage, 11% of those in similar containers at 18°C reached the first crab instar. Bacterial infections were associated with most observed mortalities. Antibiotics failed to increase the survival rates of larvae reared in glass containers.Juvenile crabs were reared in individual containers and in communal aquaria through 14 crab instars. Although instar durations were shorter at 22°C than at 18°C, mean carapace widths were significantly greater at the lower temperature. Crabs in communal aquaria at 22°C were larger than corresponding crabs at the same temperature in individual containers. Crabs reared in aquaria at 22°C reached the twelfth instar with a mean size of 90.3 mm, 195 days after hatching. Sexually mature thirteenth stage laboratory-reared crabs were mated and their offspring were reared through the ninth crab stage.     

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.     

Influence of temperature and feeding regimes on growth and notochord deformity in reared <Emphasis Type="Italic">Anguilla japonica</Emphasis> leptocephali

The high mortality rate of reared Japanese eel Anguilla japonica larvae is largely due to lower growth rate and the higher rate of deformed larvae. To establish an effective rearing protocol for this species, we examined the effects of water temperature and feeding regimes on their growth and notochord kyphosis. Larvae at 165 days post hatching were reared for 28 days at mean temperatures of 24, 25 and 27 °C, and were fed 4 or 6 times per day. Larval growth rate was significantly higher in larvae reared at 24–25 °C and fed 6 times per day. However, growth rate was significantly reduced at 27 °C, suggesting a shortage of metabolic energy due to an elevated cost of the higher basal metabolic rate at higher temperatures and low nutritional performance of currently used artificial diet. Notochord kyphosis was promoted by elevated water temperature, and two-way ANOVA showed that water temperature and feeding frequency had combined effects on the deformity. These findings suggest the importance of concurrently manipulating both environmental and nutritional factors to produce healthy eel larvae in captivity.