Artificial Spawning of Tilapia Eggs1

A stripspawning methodology was evaluated for tilapia (oreochromid) species. This technique achieved an average hatching success of 68.6 ± 3.6% (N= 31). Female fecundity and spawning frequency were dependant on both genetical and husbandry factors. Egg yields for Oreochromis niloticus, O. mossambicus, and O. niloticus±O. mossambicus hybrids averaged 4.54, 10.86 and 10.36 eggs/g female/spawn, respectively. Female broodstock that were adapted to an intensive spawning regime exhibited a significant increase in fecundity. Additionally, egg survival was not affected by hydration for up to 15 minutes prior to fertilization. Results suggest that the strip spawning of tilapia species may be an efficient method of providing viable gametes for hatchery purposes.     

Induction of heterozygous and homozygous diploid gynogenesis in Betta splendens (Regan) using hydrostatic pressure

Abstract Optimum conditions for hydrostatic pressure treatment for duplication of chromosome set in gynogenetically activated fighting fish, Betta splendens (Regan), eggs were identified. Maximum survival of heterozygous gynogens was 50%, when 2·5-min-old eggs, after insemination with UV irradiated tilapia sperm, were pressure shocked at 7000psi for 6 min. The frequency (21%) of homozygous gynogenetic fry was high, when the 34min (post-insemination) old eggs, which were inseminated with tilapia sperm, were pressure shocked for 5 min. Sex ratio of gynogenetic progeny suggested that the mechanism of sex determination in this fish is homogametic female and heterogametic male.     

Sex reversal in Nile tilapia (Oreochromis niloticus Linnaeus) by androgen immersion

Two experiments were conducted to investigate the efficacy of three androgens applied through immersion treatments on the sex ratio of Nile tilapia (Oreochromis niloticus L.) fry. In experiment 1, 14 days post‐hatching (DPH) larvae were exposed to a single immersion treatment in 17α‐methyltestosterone (MT), 17α‐methyldihydrotestosterone (MDHT) or 17α‐ethynyltestosterone (ET) at 200, 600 and 1800 μg L^?1 over 4 h (130 larvae per treatment). In experiment 2, Nile tilapia larvae were exposed to the higher androgen concentration (1800 μg L^?1) applied as either a single immersion (14 DPH) or double immersion (10 and 14 DPH) over 4 h (125 larvae per treatment). Change in sex proportion within each experiment as well as between experiments was analysed by the chi‐square test. In experiment 1, MT, MDHT and ET were equally effective in significantly increasing the proportion of males when applied at 1800 μg L^?1 (86.0%, 90.0% and 86.7% respectively). At 200 μg L^?1 none of the androgens altered sex ratio. At 600 μg L^?1, only MDHT slightly, but significantly skewed the sex ratio towards males (73.0%). In experiment 2, a single immersion treatment at 14 DPH (1800 μg L^?1) significantly increased the proportion of males, but at this time the response was significantly hormone dependent (MDHT, 100.0%; MT, 91.6%; ET, 76.9%). When compared with a single immersion, two‐immersion treatments significantly increased the proportion of males in the MT‐treated group (from 91.6% to 98.3%), decreased the proportion of males in the MDHT group (from 100.0% to 93.4%) and had no significant effect the ET‐treated group (change from 76.9% to 82.5%). The overall comparison of the sex ratio among same treatments from different experiments (a single immersion in 1800 μg L^?1) was not significantly different.     

Passive transfer of protective immunity against ichthyophthiriasis from vaccinated mother to fry in tilapias, Oreochromis aureus

Tilapias, Oreochromis aureus, were vaccinated twice with live tomites of Ichthyophthirius multifiliis in physiological saline 1 month before spawning (test group). A control group was similarly treated but with physiological saline only. Fertilized eggs were collected from the mouths of both groups and incubated until the young reached the free-swimming stage. Free-swimming fry were also collected immediately after they were expelled from the mother's mouth in other fish of the two groups. The fry were exposed to infective tomites of I. multifiliis and thereafter returned to their holding tanks. All fry obtained from the controls without mouth-brooding died after tomite exposure. However, fry with mouth-brooding before tomite exposure showed 37.3% survival. On the other hand, fry obtained from vaccinated broodstock without mouth-brooding exhibited 78.4% survival which increased to 95.3% with mouth-brooding. The protective immunity is correlated with the titres of anti-I. multifiliis antibodies in the soluble extracts of fry tissues and the mother's plasma. The results clearly indicate that protective immunity against ichthyophthiriasis “ich” in tilapia fry can not only be derived directly from the mother via eggs but also be acquired indirectly from the mouth cavity during the brooding period. The results thus suggest that proper vaccination of mothers before spawning would effectively protect fry against a protozoan disease.     

Effect of light intensity and photoperiod on Nile tilapia Oreochromis niloticus L. seed production

The objective of this study was to compare the effect of six light intensity/photoperiod combinations (2500 lux/18 h, 2500 lux/15 h, 2500 lux/12 h, 500 lux/18 h, 500 lux/15 h and 500 lux/12 h) on seed production in the Nile tilapia Oreochromis niloticus L. Each combination represented a treatment and was triplicated in 0.4‐m³ fibreglass tanks within a recirculating water system. Water temperature was maintained at 29.0 ± 1.0 °C. Males and females with mean body weights of 116.8 and 91.6 g, respectively, were stocked at a rate of eight fish/tank with a male to female ratio of 1:3. Seeds (eggs, sac fry and swim‐up fry) were collected every 2 weeks. The experiment lasted for a total of 120 days. The results showed that the 2500 lux/18 h treatment produced significantly greater (P < 0.05) total seed/tank (4944), seed kg^?1 female day^?1 (50.9), seed m^?2 day^?1 (40.3) and seed/ female day^?1 (6.7) than treatments with medium or short photoperiods (15 and 12 h day^?1 respectively) or lower light intensity (500 lux). The degree of spawning synchrony and percentage of the sac and swim‐up fry stages were significantly higher in the 2500 lux/18 h treatment than in the other treatments. Under the conditions tested in this study, seed production and spawning synchrony in the Nile tilapia may be improved by subjecting breeders to a light intensity of 2500 lux and a photoperiod of 18 h day^?1.     

Sex-Reversal of Oreochromis aureus by Immersion in Mibolerone,a Synthetic Steroid 1

Mibolerone (MI), a synthetic steroid, was used to sex-reverse undifferentiated Oreochromis aureus fry. Fry were exposed to 0.0, 0.3, 0.6, or 1.0 ppm MI in static-water solutions for five weeks (immersion treatments) or were fed a diet containing 1.0 ppm MI for four weeks in a flow-through system. Following hormone treatment, the fish were grown to over 60 mm total length prior to sex determination using gonadal squash examination. Fish immersed in 1.0, 0.6, or 0.3 ppm MI had average tissue MI concentrations of 14.4, 5.6, and 3.3 ppm, respectively. Immersion in either 1.0 or 0.6 ppm MI for five weeks resulted in an average of 82% males and 18% ovo-testicular fish (inter-sex fish) with no gonadal females being produced. Exposure to 0.3 ppm MI resulted in 78.7% males, 20.7% ovo-testicular fish, and 0.7% gonadal females. Feeding a diet containing 1.0 ppm MI resulted in 85% males, 11% ovo-testicular fish, and 4% gonadal females. Fry growth and survival were negatively correlated with the MI concentration of the immersion treatments. Exposing tilapia fry to static-water solutions of 0.6 ppm MI for five weeks appears to be a feasible method of eliminating the production of functional females. Immersion solutions should be changed at least weekly to maintain an effective hormone concentration.     

Sex-Reversal of Oreochromis aureus by Immersion in Mibolerone,a Synthetic Steroid1

Mibolerone (MI), a synthetic steroid, was used to sex-reverse undifferentiated Oreochromis aureus fry. Fry were exposed to 0.0, 0.3, 0.6, or 1.0 ppm MI in static-water solutions for five weeks (immersion treatments) or were fed a diet containing 1.0 ppm MI for four weeks in a flow-through system. Following hormone treatment, the fish were grown to over 60 mm total length prior to sex determination using gonadal squash examination. Fish immersed in 1.0, 0.6, or 0.3 ppm MI had average tissue MI concentrations of 14.4, 5.6, and 3.3 ppm, respectively. Immersion in either 1.0 or 0.6 ppm MI for five weeks resulted in an average of 82% males and 18% ovo-testicular fish (inter-sex fish) with no gonadal females being produced. Exposure to 0.3 ppm MI resulted in 78.7% males, 20.7% ovo-testicular fish, and 0.7% gonadal females. Feeding a diet containing 1.0 ppm MI resulted in 85% males, 11% ovo-testicular fish, and 4% gonadal females. Fry growth and survival were negatively correlated with the MI concentration of the immersion treatments. Exposing tilapia fry to static-water solutions of 0.6 ppm MI for five weeks appears to be a feasible method of eliminating the production of functional females. Immersion solutions should be changed at least weekly to maintain an effective hormone concentration.     

Effects of incubation water hardness and salinity on egg hatch and fry survival of Nile tilapia Oreochromis niloticus (Linnaeus)

This study examined the effects of water hardness and salinity on yolk sac larvae and swim‐up fry survival of Nile tilapia, Oreochromis niloticus (Chitralada strain), eggs during artificial incubation. Four experiments were conducted to evaluate the effects of hardness, salinity and the sources of saline incubation water. High water hardness treatments (500–4200 mg L^?1 as CaCO₃) resulted in higher yolk sac larvae and swim‐up fry survival than low water hardness treatments (50.0 and 132 mg L^?1 as CaCO₃); although yolk sac larvae and swim‐up fry survival did not differ among the high or low hardness treatments. Salinity of 4.0 g L^?1 using seawater, and 4.0 and 8.0 g L^?1 using unprocessed common salt resulted in the higher survival rate of yolk sac larvae and swim‐up fry than other salinity treatments. Yolk sac larvae and swim‐up fry survival was found to decrease with the increase in salinity and increase with the increase in water hardness. The present study demonstrated the positive effects of increased water hardness level (>132 mg L^?1) on yolk sac larvae and swim‐up fry survival. The study also showed that seawater salinity of 4 g L^?1 was the most appropriate salinity level for incubating Nile tilapia eggs.     

Observations on the reproductive performance of three mouth-brooding tilapia species in low-salinity underground water

The reproductive performance and seed production of three mouth‐brooding tilapia species, Oreochromis spilurus (Günther), Oreochromis aureus (Steindachner) and Taiwanese red tilapia hybrid, were compared in low‐salinity underground water (3–5 g L^?1) to select species with the highest reproductive rate. Two‐year‐old males and females having average body weights of 454 and 259 g, respectively, were stocked in 2‐m³ fibreglass breeding tanks (two tanks per species) at 1:3 male to female sex ratio and at average density of three fish m^?2. Seeds (unhatched eggs; yolk‐sac fry and the swim‐up fry) were collected weekly for 112 days. The results showed O. spilurus to have significantly higher (P<0.05) mean spawning parameters expressed as total seed tank^?1 (84 154), seed kg female^?1 day^?1 (284), seed m^?2 day^?1 (190.3) and seed female^?1 day^?1 (76.3), than O. aureus and red tilapia. Monthly seed production in O. spilurus and red tilapia gradually increased from May, peaked in July and declined in August, while in O. aureus, it continued to decrease from May to August. In this study, the observed production levels of seed in O. spilurus were among the highest levels reported for tilapia; therefore, O. spilurus could be selected as a potential candidate for mass seed production in commercial tilapia hatcheries.     

Overwintering performance of Nile tilapia Oreochromis niloticus (L.) broodfish and seed at ambient temperatures in northern Vietnam

Two experiments (E1 and E2) to assess the performance of tilapia broodstock and tilapia sex‐reversed fry in overwintering were conducted at the Research Institute for Aquaculture No.1 (RIA‐1) in the cold seasons of 1995–96 and 1996–97. Nile tilapia Oreochromis niloticus (L.) broodstock of the Thai, GIFT, Egypt and Viet strains were overwintered in deep and shallow ponds, as well as in deep and shallow hapas suspended in a single deep pond for evaluation of the influence of overwintering systems on the survival and growth of fish. Large (> 1 g) and small (< 1 g) tilapia seed were overwintered in deep hapas‐in‐ponds for comparison of their performance. In 1995–96, the coldest pond water temperature was 10–11 °C, and survival of tilapia broodfish overwintered in deep and shallow hapas‐in‐ponds was 99.6–100%. This was significantly (P < 0.05) higher than fish stocked in deep and shallow ponds (74.4–90%). The survival rate of larger monosex tilapia fry was 54%, which was significantly (P < 0.05) higher than that of smaller fry (33.4%). In 1996–97, the lowest pond water temperature was 15.8 °C, and fry showed similarly high survival rates in all treatments (97–100%). There was no significant difference between fry in the two size classes. The results of this study clearly indicate that hapas‐in‐ponds are useful for reducing the risk and improving the survival of tilapia broodstock and fry in the cold season. Differences in the decline in ambient temperatures year on year mean that the need for special overwintering conditions varies. Hapas‐in‐ponds are a low‐cost overwintering method that can be one of the appropriate strategies for tilapia seed production under the variable, cool temperature regimes in northern Vietnam.     

Genetic parameters and correlated responses in female reproductive traits in the GIFT strain

The effect of selection for greater growth rate in the GIFT strain on traits related to female reproduction (weight at spawning, number of eggs, number of fry, total weight of fry and number of dead fry) was studied. Available records comprised 10 generations of data from a total of 935 breeding females with known pedigree. Female body weight at spawning was 255 g, whereas the averages for number of eggs, number of live fry at hatching, number of dead fry and total fry weight per spawning were 1444, 908, 64.90, and 7.24 g respectively. Heritabilities for reproductive traits were low to moderate (0.20 for number of eggs, 0.16 for number of hatched fry and 0.11 for fry weight per female at spawning). The genetic correlations between female body weight at spawning and reproductive traits were very low to low (0.01 to 0.31) and not significantly different from zero. The genetic correlations among reproductive traits (i.e. number of eggs, number of hatched fry and fry weight) were high (0.75 to 0.92). Phenotypic correlations were consistent with the genetic correlations, ranging from 0.56 to 0.85. Correlated responses in reproductive traits measured as differences in least squares means between Selection and Control lines were positive and significant (except for the number of dead fry) when age of females at spawning was fitted as a covariate. However, there were no significant differences in all studied traits when body weight of the female at spawning was fitted as a covariate within lines. This indicates that the greater reproductive rate was due to the greater size of females in the Selection line, but the efficiency of reproduction per unit weight of female did not change as a consequence of selection for growth.     

Fry Production of Shire River Tilapia Oreochromis shiranus at Two Broodstock Sex Ratios1

Abstract.— Shire River tilapia Oreochromis shiranus broodfish were stocked at a density of 1.25 fish/m² and sex ratios of either 1:1 or 1:3 (males: females). Two weeks after stocking, fry collection began. Fry were then harvested weekly for 9 wk with a fine-meshed dip net operated from the pond bank for 1.5 h each morning and afternoon. Ten weeks after fry collection began, all ponds were drained and completely harvested. Over the entire 84 d, fry production averaged 0.78 fry/m² per d and did not differ (P < 0.05) between treatments. Fry production per female was significantly higher (P < 0.02) in ponds stocked at a 1:1 sex ratio (111 fry/female) compared to a 1:3 sex ratio (66 fry/female). To avoid inbreeding without sacrificing production, a broodstock sex ratio of 1:1 can safely be used when producing O. shiranus fry at a density of 1.25 fsh/m² in earthen ponds. Competition among females is a possible cause of reduced fry production in densely-stocked brood ponds.     

Improving spawning synchrony in the Nile tilapia, Oreochromis niloticus (L.)

Abstract. The development stage and number of seed (eggs and fry) removed from individual incubating Oreochromis niloticus (L.) broodfish at 10-day interharvest intervals (IHI) was compared with the harvest of free-swimming fry from undisturbed fish held in a tank within the same system. Spawning synchrony and productivity were compared for (1) total exchange of females for ‘conditioned’ females after each harvest, (2) exchange of only spawned females, and (3) return of females back into the spawning tank. Improved synchrony and seed production were positively related to removal of eggs and fry from incubating females and could have important implications for broodstock management in commercial hatcheries. Allowing fish to remain undisturbed in clear water tanks may lead to inhibition of spawning activity related to the formation of hierarchies. Individual weight loss by females during incubation was correlated with stage of seed harvested and thus with timing of spawning during the interharvest interval.     

Role of thyroid hormones in tilapia larvae (Oreochromis mossambicus): I. Effects of the hormones and an antithyroid drug on yolk absorption,growth and development

Treatment of one-day old yolksac larvae of tilapia (Oreochromis mossambicus) by immersion in 0.05 ppm T₄ or 0.01 ppm T₃ significantly accelerated the differentiation and growth of all the fins, particularly pectoral and tail fins. Both the treatments also significantly accelerated yolk absorption and transition to free-swimming activity in the larvae. The treatments also significantly accelerated the growth of the larvae, with T₃ at 0.01 ppm having a greater effect than T₄ at 0.05 ppm. The yolk conversion efficiency was found not to be significantly affected by the hormone treatments but the treated larvae exhibited an increased heart beat, suggesting metabolic stimulation by the hormones.On the other hand, yolk absorption and free-swimming activity were significantly delayed in tilapia larvae immersed in 25 ppm solution of an antithyroid drug, phenylthiocarbamide (PTC). PTC also retarded the growth of the larvae. T₄ (0.05 and 0.10 ppm) or T₃ (0.01 and 0.02 ppm) therapy removed the PTC-inhibition,albeit not completely, suggesting that thyroid hormones are involved in the larval growth and development of tilapia.     

An evaluation of two types of containers for the artificial incubation of Oreochromis eggs

Abstract. Conical and round-bottomed incubating containers were evaluated for efficiency in producing Oreochromis fry. For Orcochromis niloticus (L.) and Oreochromis mossambicus (Peters): 0-, 12-, 24-, 48- and 72-h-old egg clutches were artificially incubated at 28°C in conical and round-bottomed containers. Hatching occurred within 72–84h and 90–102h after fertilization respectively compared to 96–120h for naturally incubated egg clutches. No significant differences (P > 0·05) were found between the hatch and survival rates of O. niloticus and O. mossambicus fry or between fry from the various ages of eggs. The type of containers, however, significantly (P < 0·05) influenced the hatchability and survival rates, the overall survival rate from fertilization being 60% and 85% for conical and round-bottomed containers respectively. Possible reasons for these differences are discussed. The feasibility of using the superior round-bottomed containers for artificial egg and fry incubation and the advantages for broodstock management to mass produce Oreochromis fry are discussed.     

Effect of the use of the microalga Spirulina maxima as fish meal replacement in diets for tilapia, Oreochromis mossambicus (Peters), fry

The present study addresses the use of the microalga Spirulina maxima as a protein source in diets for tilapia, Oreochromis mossambicus (Peters), fry. Animal protein was replaced with algae protein at ratios of 20%, 40%, 60%, 80% and 100%, and the substitution effect was compared with a control diet in which fish meal was the sole protein. An additional 100% spirulina protein diet was supplemented with phosphorous to test for possible mineral deficiency in the plant-protein-based diet. The six treatments were tested in triplicate in a closed-recirculating system where the fish were fed by hand at 6% of their body weight. After a 9-week feeding period, the growth rate and protein utilization of fish fed the diet with 20% and 40%Spirulina were elevated and not significantly different (P>0.05) from those fed the control diet. Further increases in the alga protein content significantly decreased the growth and feeding performance. The addition of P to the 100%Spirulina diet slightly improved performance in comparison to the same diet without P. None of the treatments produced any clear adverse effects on carcass composition. It is observed that Spirulina can replace up to 40% of the fish meal protein in tilapia diets.     

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.     

Importance of maternal size on the reproductive success of perch,Perca fluviatilis,in small forest lakes: implications for fisheries management

Abstract Abundance, sex ratio and size structure of perch, Perca fluviatilis L., populations were studied in two forest lakes. The influence of maternal size on the amount and quality of eggs and larvae was investigated, and the effect of the spawning stock’s length structure on population egg and fry production was evaluated. The importance of large females was essential for the reproduction of perch. Large perch spawned more and bigger eggs that had higher hatching percentage resulting in considerably higher fry production. Larvae of large females were heavier and survived longer with bare yolk sac reserves. The relation between egg dry weight and female length differed between the study lakes suggesting varying maternal influence in different environments. Decrease in the share of large individuals in a perch population can substantially reduce the amount and quality of larvae produced. The results can be applied to improve the sustainability of perch fisheries.     

Spawning performance and seed production from hybridization between Oreochromis spilurus and the GIFT strain of the Nile tilapia Oreochromis niloticus

This study compared the spawning performance of four crosses between the salt‐tolerant tilapia Oreochromis spilurus and the fast‐growing genetically improved farmed tilapia (GIFT) strain of the Nile tilapia Oreochromis niloticus: (1) O. spilurus♀×O. spilurus♂ (SS); (2) Nile ♀× Nile ♂ (NN); (3) Nile ♀×O. spilurus♂ (NS) and (4) O. spilurus♀× Nile ♂ (SN). In each cross, males and females having mean weights of 157 and 115 g, respectively were stocked in 0.43 m³ tanks at a male to female ratio of 1:3. Seeds (unhatched eggs, yolk‐sac fry and free swimming fry) were harvested biweekly for 127 days. Viable spawns resulted from all crosses. The NN cross produced the highest total seeds tank^?1 (2890), seeds (kg female)^?1 day^?1 (48.3), seeds m^?2 day^?1 (23.3) and seeds female^?1 day^?1 (7.9), followed by the SS and SN crosses. The NS cross had the lowest fecundity. Lower spawning parameters in the NS and SN crosses may be attributed to the lower social compatibility between the males and females compared with that of the pure parents. The survival and growth of the offspring from the four crosses will be compared in seawater (37–40 g L^?1) to assess whether hybrid vigor was produced.     

葛洲坝下中华鲟产卵场卵苗输移过程的数值模拟

基于水动力学计算的基本原理,采用三维水动力模型及粒子跟踪技术,模拟了中华鲟(Acipenser sinensis)卵苗输移过程。将目前葛洲坝下中华鲟产卵场区域划分为9个子区域,将粒子赋予中华鲟卵粒特征,反演了中华鲟2009年自然繁殖卵苗沿河道输移路线和扩散过程。在划分的9个区域中,区域1、2、5为极有可能的产卵位置。模拟得到的产卵位置、卵输移路径及输移时间与实际监测情况基本一致。模拟结果显示,卵苗输移受天然河道地形和水流流场变化的影响较大。