Influence of egg size on the growth,onset of feeding,point-of-no-return,and survival of unfed Oreochromis mossambicus fry

The variation in egg size within and between egg clutches of O. mossambicus, and the subsequent influence of mean egg size on growth, feeding incidence and survival of unfed fry were investigated.The individual egg sizes within 90% of the egg clutches examined were normally distributed and the coefficient of variation of egg size within clutches ranged from 7.4% to 15.4%. Fry emerging from the small, medium and large egg size groups reached their maximum length and weight at 9, 9 and 12 days after hatching, respectively. Maximum attainable fry length and weight were significantly correlated with egg size (r = 0.885 and 0.947, respectively, with P < 0.01).Egg size had little influence on the onset of feeding. Fry were capable of exogenous feeding within 6 to 7 days of hatching. Fry originating from small and medium egg size classes reached the point-of-no-return at 15–16 days after hatching compared to 21 days for fry from the large egg size class. The mean survival time (ST₅₀) of fry on their yolk reserves was significantly correlated (r = 0.923; P < 0.01) with their original mean egg weight and ranged from 9.5 days for fry hatching from 0.91-mg eggs to 21 days for fry from 1.93-mg eggs.     

Genetic certification of presumed hybrids of blue × red abalone (Haliotis fulgens Philippi and H. rufescens Swainson)

Presumed hybrids between Haliotis rufescens and H. fulgens abalones, produced in a commercial abalone laboratory, were evaluated for progeny viability, gonad characteristics and for their ‘true’ status as hybrids by means of allozyme and microsatellite analyses. Four out of 10 evaluated allozyme loci proved to be useful for the genetic certification of hybrids, Gpi, Mdh‐1, Mdh‐2 and Sod, as they had exclusive alleles for each of the abalone reference species from which the presumed hybrids were produced. Three microsatellite loci were also evaluated for their usefulness in abalone hybrid certification. Two were not useful for hybrid certification as the reference abalone species shared some of the same alleles. The third loci (Hka 56) also had shared alleles between the two species, but at very different frequencies. Therefore, this permitted a presumptive certification of hybrids, which, however, was not error‐proof as two allozyme certified hybrids were wrongly classified as H. rufescens rather than as hybrids. Progeny viability of the only female certified to be a hybrid was significantly lower compared with one viability of the other females spawned, which were certified as H. rufescens. However, the number of eggs spawned by the only certified hybrid female was as large as those spawned by females certified as H. rufescens. Gonads of abalones sampled for the macroscopic appearance of sterility indicated that in the absence of any gonad development, no distinctive difference allows for hybrid identification, as there were undifferentiated individuals that were both hybrid and non‐hybrid. On the other hand, two certified hybrid males were characterized by spermatocytes being the most abundant gamete type, although one had some spermatozoa present, indicating only partial sterility. Among the two female hybrids found, vitellogenesis was observed to proceed up to vitellogenic oocytes.     

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.     

Reproductive performance in female strains of Nile tilapia, Oreochromis niloticus

The Nile tilapia is among the most cultivated tropical fish in the world, yet little is known about the variations in reproductive characteristics among different strains. There is an interest in evaluating the reproductive performance of females of three tilapia strains. All strains were represented in equal proportion (n = 225), being named as Supreme (SUP), Premium Aquabel (PA), and Chitralada (CHI). These fish were cultivated for 7 weeks in the Aquabel Pisciculture Station (Brazil), from January to March 2011. The PA was the largest strain, with the highest values in all the morphometric parameters we analyzed (weight, total length, standard length and body depth). Among the evaluated reproductive parameters, the PA strain differed significantly from the other two in number and weight of eggs/female, volume of eggs/spawn and number of eggs/kg of fish. The percentage of non-spawning females in the SUP and CHI strains differed significantly from one another, while results for PA showed intermediate values and no significance compared to the other strains (P > 0.05). Among the reproductive parameters analyzed, the percentage of spawned females/week, more than one spawns during 7 weeks, and hatching rate showed no significant differences between strains (P > 0.05). There was a significant correlation (r = 0.69) between water temperature and percentage of spawned females/week. When evaluating the interval between two consecutive spawns, we observed that periods of 21 days were the most frequent in all strains. In conclusion, the strain that showed the best results in all morphometric and in most reproductive parameters we evaluated was the PA.     

Application of controlled-release,GnRHa-delivery systems in commercial production of white bass X striped bass hybrids (sunshine bass), using captive broodstocks

Hatchery-produced white bass (Morone chrysops) and striped bass (M. saxatilis) reared to maturity in a commercial aquaculture facility, were successfully spawned using controlled-release delivery systems containing the gonadotropin-releasing hormone analog DAla⁶, Pro⁹[NEt]-GnRH (GnRHa). Two-year-old white bass females (mean weight, 0.81 kg) were implanted with different polymer-based, GnRHa delivery systems at doses ranging from 40 to 89 μg GnRHa kg⁻¹ body weight. GnRHa treatment on 20 February 1994, when females contained oocytes up to 720 μm in diameter, induced ovulation of all fish between 35 to 82 h after treatment. The white bass eggs produced were fertilized with sperm from striped bass for the production of sunshine bass. An average of 294500 eggs kg⁻¹ were produced, with a mean fertility of 81.2%, 24 h survival of 46.5%, and overall hatching success of 45%. Survival from hatch to 30 days post-hatch was 78% and the fry weighed between 0.07 and 0.1 g. Overripening of eggs began within 1 h from ovulation and maximum fertilization (60%) was observed when eggs were stripped 0.5 h after ovulation. Fertilization success decreased thereafter to 31% and 10% by 1 h and 3 h after ovulation, respectively. Control fish not treated with GnRHa did not show any signs of final oocyte maturation during the period of the study. GnRHa administration via controlled-release delivery systems appears to be a very effective method for inducing high fecundity ovulation of captive white bass broodstocks, and producing eggs of high fertility and hatching success.     

Salinity tolerance of Nile tilapia fry (Oreochromis niloticus), spawned and hatched at various salinities

Fertilized eggs of the Nile tilapia (Oreochromis niloticus L.) spawned in freshwater, were removed from mouthbrooding females, 1 day post-spawning and artificially incubated at elevated salinities. At 6 days post-hatching, mean survivals of 85.5, 84.4, 82.5, 56.3, 37.9, 20.0 and 0% were recorded for broods incubated at salinities of 0, 5, 10, 15, 20, 25 and 32 ppt, respectively. Fertilized eggs exhibited a 96-h median lethal salinity (MLS-96) of 18.9 ppt, a value identical to that of 7- to 120-day-old fry and fingerlings. Fertilized eggs exhibited a higher median survival time (ST₅₀ = 978 min) than 7- to 395-day-old fry and fingerlings (ST₅₀ = 28.8–179.0 min).The salinity tolerances of fry spawned at various salinities and fry spawned in freshwater but hatched at various salinities, were determined using the median survival time (ST₅₀), mean survival time (MST) and 96 h-median lethal salinity (MLS-96) indices. For comparative purposes, fry spawned and hatched in freshwater were acclimatized to various salinities and their salinity tolerance determined. Fry salinity tolerance progressively increased with increasing salinity of spawning, hatching, or acclimatization. However, at equivalent salinity, early exposure (spawning) produced progeny of comparatively higher salinity tolerance than those spawned in freshwater and hatched at elevated salinity. Similarly, at equivalent salinity, progeny spawned in freshwater but hatched at elevated salinity exhibited higher salinity tolerance than those spawned and hatched in freshwater, then acclimatized to an elevated salinity.The utility of these methods of early salinity exposure toward the saltwater culture of tilapias is discussed.     

Growth and maturation of Pacific saury Cololabis saira under laboratory conditions

This study details the growth and maturation processes of Pacific saury Cololabis saira from eggs to first spawning under laboratory conditions. They were reared at 20°C, and fed almost to satiation every day. There was no significant difference in the knob length (KnL) between males and females, and so data for both sexes were combined in the following Gompertz growth formula: KnL _t  = 277.1 exp[?exp(?0.015 (t ? 83.8))]. The first spawning was observed 243 days after hatching (DAH). At the beginning of spawning, when the mean KnL was about 250 mm, only several hundred eggs were spawned at most. The spawning continued, and the number of spawned eggs increased notably after 260 DAH. Correlation and stepwise multiple regression analysis of the gonad somatic index (GSI) of Pacific saury versus KnL, CF, and DAH revealed that only DAH (R = 0.88 and 0.72 for males and females, respectively) was significantly correlated with GSI of Pacific saury (P < 0.001). This result suggests that DAH is one of the most influential factors for maturation in this species.     

Effect of hybridization on reproductive performance of Oreochromis karongae,Oreochromis shiranus and Oreochromis mossambicus

The study assessed the effect of hybridization on reproductive performance of Oreochromis karongae, Oreochromis shiranus and Oreochromis mossambicus for a period of 120 days. Number of eggs per batch, number of females spawned, relative fecundity, egg size, hatching period, hatchability and hatchling survival were assessed. The results revealed higher number of eggs per batch and relative fecundity in the crosses where O. shiranus and O. mossambicus were females than female O. karongae. The results also revealed that egg size, hatching period, hatchability and hatchling survival were species specific. Significant differences were noted for number of eggs and larvae produced by the three species (p < .05). Interspecific and pure crosses for the same female species did not differ significantly for the number of eggs per batch, relative fecundity, egg size, hatching period, hatchability and hatchling survival. However, number of female spawned was found to be higher in the interspecific crosses of female O. karongae than in pure cross of O. karongae. Findings from this study suggest that hybridization can be used to improve reproductive performance of O. karongae as the females spawned increased, and it is a value addition in aquaculture management of indigenous species.     

Genetic characterization, morphometrics and gonad development of induced interspecific hybrids between yellowtail flounder, Pleuronectes ferrugineus (Storer) and winter flounder, Pleuronectes americanus (Walbaum)

Viable interspecific hybrids between yellowtail flounder (Pleuronectes ferrugineus, Storer) and winter flounder (Pleuronectes americanus, Walbaum) were produced by artificial insemination of yellowtail flounder eggs with winter flounder sperm. However, mean fertilization rate, hatching success and early survival up to 3 weeks post hatch were significantly lower than those of parental pure cross controls (P < 0.01). Overall, cytogenetic traits (karyological analysis and estimation of cellular DNA contents using flow cytometry) of hybrid flounder were intermediate between the two parental species. Microsatellite assay was used to distinguish the parental genomes in the hybrids; in most cases, one allele was specific to each of the parents. Morphometrics assessed by body proportions indicated that hybrids generally displayed a morphology intermediate between the maternal and paternal species. Interspecific hybrids exhibited abnormal and retarded gonad development in both sexes based on histological analysis of gonads from adult fish. The sterility of the hybrids presents a significant advantage for their use in aquaculture, as potential escapees would not be capable of reproducing in the wild and contaminating natural stocks.     

锯缘青蟹卵膜变化与卵子附着研究

利用光镜和电镜观察了锯缘青蟹成熟卵及其受精后卵膜变化和卵子附着特征。锯缘青蟹成熟卵子卵膜有三层即外层、内层和质膜。卵子产出后,无论受精与否,外层和内层卵黄膜形成壳膜,与卵子附着有关。刚产出的卵子卵膜具有溶胶性和延展性,卵子与刚毛表面之间或卵子之间接触便粘在一起,由于刚毛摆动和卵子的重力作用,形成卵柄或卵索。卵子受精后,发生皮层反应形成受精膜。由壳膜和受精膜构成的孵化膜为初级卵膜,保护胚胎发育,直至     

Maximizing lobster, Homarus gammarus (L.), egg and larval viability

The viability of batches of larvae reared to produce lobsters, Homarus gammarus (L.), for stock-supplementation experiments varied widely and rendered the timing and numbers of juveniles available for release unpredictable. Egg lipid reserves, time of hatching, exposure to low salinity during incubation and the influence of feeding regimes on water quality during larval culture were among the factors judged most likely to have affected viability. There was considerable variation in the lipid content of eggs from different females captured in 1989 and 1990. The proportion of lipid in eggs from females caught in 1990 was higher (10-20%) than that in eggs from females caught in 1989 (6-11%). The fatty acid content of eggs declined 72-80% during development although the overall proportions of fatty acids remained similar. Analysis of eggs and larvae from a single brood showed that rapidly developing eggs and the larvae that hatched from them contained greater triacylglyceride lipid reserves (by 49% and 15% respectively) than those which developed more slowly and hatched later. Exposure to reduced salinity (below 29 psu) prolonged development (by 30%), increased losses (to > 50%) and reduced the ratio of n-3:n-6 fatty acids (from 35-48 to 18-29) of eggs being incubated by captive, wild-caught, female lobsters. Larvae hatching from eggs held in reduced salinity (23 psu) survived less well (3% compared with 15%) than those incubated in sea water of 29 psu. The rate and degree to which fouling organisms became attached to larvae was related to feeding regime but not to development rate. A diet of mysids supplemented with mussel produced most fouling, generally poorer growth and a higher incidence of moulting abnormalities than a diet of mysids supplemented with Artemia nauplii. Among larvae fed Artemia, those developing early were significantly larger at instar 4 than late developers (56.4 mg cf. 49.8 mg, P < 0.05), but such differences in weight were not maintained by juveniles during the following 31 days of culture. The ecological and aquacultural implications of the results are discussed.     

Breeding of Penaeus monodon Fabricius in laboratory recirculation systems

From March to May 1978 over 2 million nauplii were hatched from 34 batches of eggs obtained from five Penaeus monodon females. Females of 50–63 mm carapace length, with one eyestalk removed, spawned viable eggs repeatedly within intermoult periods of 20–30 days indicating that one impregnation was sufficient to fertilize several batches of eggs spawned within one intermoult period. A fresh impregnation was necessary after each moult. The number of eggs per batch varied from 19 000 to 460 000 (mean 217 635) and did not decrease with successive batches. The mean hatch-rate was 30.5% and the mean number of nauplii per brood was 66 000. There was a tendency to a lower hatchrate for batches of eggs produced towards the end of an intermoult period. Samples of larvae from 15 broods were cultured to the post-larval stage at densities of 40–250 larvae/l. Mean survival in 3-1 cultures was 79% but was <13% in larger-scale trials.     

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   

Larval performance of matrinxã, Brycon amazonicus (Spix & Agassiz 1829), after maternal triiodothyronine injection or egg immersion

This study compared the larval performance of matrinxã, Brycon amazonicus, after maternal triiodothyronine (T₃) injection or egg immersion of T₃. In the first experiment, three groups of females (n=4) induced to spawning received pituitary extract (CPE) and a corn oil injection (control), or CPE plus 10 mg or 20 mg kg^?1 bw T₃ dissolved in corn oil (experimental). Larvae were sampled for body weight and length measurement at hatching (0 h) and 12, 24, 36, 48 and 60 h thereafter. Hatching time, hatching success and abnormal development were monitored. In the second experiment, fertilized eggs from four females were immersed in T₃ solutions (0, 0.01, 0.05 and 0.10 mg L^?1) and larvae were sampled at hatching (0 h) and 6, 18, 30, 42, 54, 126 and 198 h thereafter. Hatching time was not affected by either means of hormone treatment. Abnormalities decreased as the T₃ concentration increased in larvae from T₃‐treated broodfish but the number of dead larvae increased proportionally. Larvae from T₃‐injected females had higher weight from 24 h after hatching and greater length from hatching, while the weight of larvae produced from T₃‐immersed eggs changed at 198 h and length from 126 h of rearing. Both routes of T₃ administration affected the early growth of matrinxã but the effect was observed earlier when broodstock females were injected.     

Incubation of European Squid (Loligo vulgaris Lamarck, 1798) eggs at different salinities

Loligo vulgaris is a commercially important squid throughout the Mediterranean region and is a candidate species in biomedical and aquaculture research. Some loligo species (L. opalescens, L. forbesi, Sepiteuthis lessoniana) have now been cultured through some successive generations in closed, recirculating seawater systems. The effects of salinity on hatching European Squid (L. vulgaris Lamarck, 1798) eggs were investigated during November 2004. The egg capsules were incubated directly in salinity of 32, 34, 36, 38, 40, 42 and 37 g L^?1 (control group) at 19.8°C (SD 1.2°C), and a photoperiodicity of 12 h light:12 h dark for 16–23 days before hatching. In all treatments, the eggs were developed and hatched normally after 16–22 days at 32 g L^?1, 17–22 days at 34, 18–21 days at 42 g L^?1, 18–22 days at 36 and 40 g L^?1, 19–22 days at 37 g L^?1 and 19–23 h at 38 g L^?1. In the experiments, the highest hatching rate and hatching success (HS) of the eggs were obtained at 38 g L^?1 (hatching rate: 100% (SD 0%) and HS: 96.7% (SD 3.5%)) and the lowest hatching rate at 42 g L^?1 (hatching rate: 3% (SD 6%) and HS: 0%). Dorsal mantle lengths (DML) of new hatchlings ranged from 2.08 to 2.80 mm. The present study showed that salinity affects the hatching rate and HS of eggs and first hatching time and DML of paralarvae in L. vulgaris. The squid eggs at stage 11 (I) can tolerate 5 g L^?1 reduction and 3 g L^?1 increase in salinity.     

Induced spawning of Asian catfish, Clarias batrachus (Linn.): effect of various latency periods and SGnRHa and domperidone doses on spawning performance and egg quality

An experiment was conducted to induce ovulation in Asian catfish, Clarias batrachus, by a single injection of SGnRHa (d ‐Arg⁶, Trp⁷, Leu⁸, Pro⁹, Net) in combination with domperidone. The effects of latency periods, 11, 14, 17, 20 and 23 h, and doses of inducing agent, 10 μg SGnRHa+5 mg domperidone, 20 μg SGnRHa+10 mg domperidone, 30 μg SGnRHa+15 mg domperidone and 40 μg SGnRHa+20 mg domperidone kg^?1 body weight, were studied on the total egg output, stripping response, fertilization, hatching and normal larval production. The highest (P<0.05) number of eggs were stripped at 23 h of post injection of 20 μg SGnRHa+10 mg domperidone kg^?1 female body weight. The highest (P<0.05) stripping response was observed when the females were stripped at 20 and 23 h latency, at all dose levels of the inducing agent. The eggs stripped at 11 h latency did not fertilize, and hence did not hatch irrespective of administration of any dose levels of the inducing agent. The fertilization and hatching per cent of eggs had significantly increased (P<0.05) with increase in latency period to 14–23 h at a dose of 20 μg SGnRHa+10 mg domperidone. The latency period of 14–17 h, and dose of 20 μg SGnRHa+10 mg domperidone and 30 μg SGnRHa+15 mg domperidone kg^?1 of female, was found to be suitable to obtain best spawning performance, and good‐quality egg and larval production in C. batrachus.     

Induced spawning of sea bass, Lates calcarifer, and rabbitfish, Siganus guttatus, after implantation of pelleted LHRH analogue

Captive Lates calcarifer broodstock at Tigbauan, Iloilo (Philippines) were implanted with cholesterol-based pellets of the LHRH analogue D-Trp⁶-desGly¹⁰-LHRH ethylamide or D-hArg(Et₂)⁶,Pro⁹-NHet-LHRH at doses between 9.0 and 23.5 μg/kg body weight. In May, one of ten LHRH-treated females released partially hydrated ova into the tank 4 days after implantation. In July, at least one (and probably four) of five LHRH-treated females spawned in the tank 2 days after implantation; 2.6 million hatchlings were collected. In August, both LHRH-treated females spawned in the tank 2 days after implantation; 978 000 hatchlings were collected. None of the sham-operated control fish spawned in any of the experiments.Captive Siganus guttatus broodstock implanted with silastic-based pellets of the LHRH analogue D-Nal (2)⁶ LHRH spawned 1–2 days earlier than sham-operated controls.     

The influence of captive breeding on the fatty acid profiles of Salminus hilarii (Characiformes: Characidae) eggs and larvae

In addition to the strong influence of the broodstock diet on the development and survival of offspring, domestication may also interfere with the larval life success. We obtained eggs from wild and domesticated Salminus hilarii females and domesticated males. Wild females were caught in the Tiete River and tributaries, and the domesticated females were born three years before the beginning of the experiment in the Ponte Nova Fish Farm. Animals from both groups were fed with the same feed to exclude feed variables. The eggs and larvae were sampled at 0, 8, 16, and 28?h after spawning (HAS), with the last sampling (28 HAS) coinciding with hatching time. After hatching, samplings proceeded at 32, 48, 66, and 96 HAS, with the last sampling (96 HAS) corresponding to the end of yolk sac consumption. Finally, the last experimental period was during the larvae exogenous feeding phase, at 102, 118, 166, and 214 HAS. Our data revealed that domestication of S. hilarii females influenced fatty acid (FA) metabolism during embryo and larva development. However, the structure of membrane phospholipid FA remained mostly stable, with changes principally in the neutral fraction. When the external conditions, mainly water and feed quality, remained constant, domestication of S. hilarii females did not significantly affect the structural FA composition but influenced the selectivity of consumption and/or storage of specific FA.     

Improving cold storage of subitaneous eggs of the copepod Acartia tonsa Dana from the Gulf of Mexico (Florida – USA)

Developing methods to store copepod eggs is necessary to increase the availability of copepods as a live food for the aquaculture industry and aquarium trade, and also to allow the exchange of copepods between researchers. The present study, evaluated the effect of glucose and two antibiotics (kanamycin sulphate and oxytetracycline HCl) on extending the shelf life of cold-stored subitaneous Acartia tonsa eggs. Also, egg development effects on the survival of the eggs were tested. Glucose did not have any significant effects on the survival of the eggs. However, the addition of antibiotics to the storage vials resulted in an increase of the survival of the eggs. In the best case, the shelf life of the eggs was almost doubled. After 7 days, the kanamycin+glucose treatment led to a hatching success of 86±1% of the hatchable eggs, while the untreated eggs presented a hatching success of 47±6%. However, long exposure to high concentrations of antibiotics was lethal to the copepod eggs. After more than 30 days of exposure to 100 mg L⁻¹ of oxytetracycline, the survival of the eggs was lower than in the untreated samples. After 45 days, oxytetracycline-treated eggs (100 mg L⁻¹) presented a hatching success of 4–5% while the non-stored eggs still had a hatching success of 9%, and the eggs treated with a lower concentration of antibiotics (10 mg L⁻¹) showed a hatching success up to 21–23%. The size of the nauplii in all trials tended to decrease as the period of cold storage at 1°C increased. We consider that the use of antibiotics at the right dosage to be a means to increase the storage capacity of the Gulf of Mexico strain of A. tonsa eggs, which do not show any capacity to be stored for long periods of time, compared with some other strains. In addition eggs that were between 5 and 7 h old survived longer when stored in the cold than eggs, which were freshly spawned or closer to hatching.     

Controlled propagation of the African catfish,Clarias lazera (C. & V.): II. Artificial reproduction

To optimize the artificial reproduction of C. lazera for aquaculture, experiments were carried out on short-term sperm conservation as well as hypophysation and stripping of the females.When the sperms were stored at 5°C for 24 h, their fertilizing capability was reduced by 4% compared with freshly obtained sperm. However, dilution in a 0.9% naCl solution (up to 10^?3) gave an average 9% increase of hatching success. This finding enables the use of one competent male to fertilize the eggs of many females. An alternative application of the finding enables homoplastic hypophysation, using the fresh pituitary of the male to induce ripening of the female, while the sperms are stored for later use.Correct timing of stripping of the females in relation to hypophysation proved to be critical for obtaining good hatching results. This was increasingly so when temperatures were high. The best results in these experiments were obtained when stripping took place 21, 11 or 7 h after hypophysation at 20, 25 and 30°C, respectively.At this time the eggs were flat, with the cytoplasm concentrated at the animal pole as a reddish-brown spherical cap. The incubation period of the eggs decreased with increasing temperature. In all instances a large proportion of deformed fry occurred wiich was inversely related to the hatching percentage. Incubation without a regular water exchange gave 4% more hatching, 6% less deformation and a shorter incubation period than incubation with water exchange.Hypophysation was repeated four times with 1-, 2- or 3-week intervals and resulted in successful stripping, fertilization and hatching of the eggs after each hypophysation.