Gametogenesis and breeding of Ostrea edulis on the west coast of Ireland

Gametogenesis, spawning and larval production of the European flat oyster Ostrea edulis L. were studied in sublittoral beds in Ballinakill Harbour and Kilkieran Bay, Co. Galway, from April 1977 to November 1978 and from November 1978 to May 1980 respectively. Histol ogical preparations of gonads and percentages of oysters brooding larvae were used to monitor breeding.Maturation began in March/April with ripe gametes appearing in some oysters in mid-May. Incubating oysters were observed from mid-June to August/September. Spent oysters were numerous in September. Gametogenesis was at a minimum from October to February depending on the year of study. Ripeness as measured by four different parameters was observed to peak around 29 June 1977 and 4 July 1978 in Ballinakill Harbour, and on 10 July 1979 in Kilkieran Bay. The onset of maximum ripeness in both populations could be predicted using the formula:

$\text{D=}\text{∑}\text{i=1}\text{N}\text{(t}{}_{\mathrm{i}}\text{? t}{}_0$

where D is the thermal constant in degree-days, n = the number of days required to reach ripeness, t_i = temperature to which the oysters were exposed daily (°C) and t₀ is the developmental zero for gametogenesis. The mean thermal constant as calculated from the gametogenesis study was 554.52 ± 44.52 degree-days. Redevelopment of gametes began during late winter at mean seawater temperatures above approximately 7.0°C.     

Dependence of Coregonus albula embryogenesis rate on the incubation temperature

Eggs stripped from Coregonus albula were incubated at different constant temperatures. The duration of embryogenesis varied from 183 days at 1.1°C to 45 days at 9.9°C. We describe the course of embryogenesis using 16 easily recognizable developmental stages (DS j). Development rate (DR j) for any given stage (DS j) is expressed as the reciprocal of time (in days) from fertilization to attainment of a given developmental stage. The generalized equation relating rate of development to stages DS j with respect to temperature (x) is

The values of DR to the “eyed egg” stage and to 50% hatch, expressed as percentage per day of the total development period, were computed and tabulated for temperatures ranging from 0.1 to 9.9°C. To verify the derived regression model we observed the course of embryogenesis of C. albula eggs incubated in a commercial hatchery at fluctuating temperatures. The observed times of attainment of the successive developmental stages were compared to the predicted times based on mean daily water temperatures. The time observed agreed well with times predicted by the model; the only exception was the time of hatching, which was systematically overestimated (5 to 7 days) by the model. This was possibly due to the influence of dissolved oxygen on the time course of hatching processes, which was not considered in our regression model.     

The inhibition by ammonia of population growth of the rotifer, Brachionus rubens, in continuous culture

For the safe maintenance of microalgae and rotifers in mass culture, it is necessary to know the exact threshold concentration of ammonia for rotifers. In order to determine this threshold concentration, the continuous culture technique was used as a sensitive method to determine the influence of ammonia on the reproduction rate of the rotifer Brachionus rubens. As expected, only unionized (free) ammonia affected the population growth. Up to a concentration of 3 mg $\text{NH}{}_3\text{-N}\text{l}$ the reproduction of Brachionus was unaffected. In the range of 3–5 mg $\text{NH}{}_3\text{-N}\text{l}$ the reproduction rate decreased, although no animals were killed. This decrease was reversible and could be overcome by lowering the NH₃-N concentration. At concentrations over 5 mg $\text{NH}{}_3\text{-N}\text{l}$ the rotifers died within 2 days.     

The effects of thermal amplitude on the growth of Chinese shrimp Fenneropenaeus chinensis (Osbeck, 1765)

Effects of thermal amplitude of diel fluctuating temperature on the growth, food consumption, food conversion efficiency and apparent digestibility coefficient of Chinese shrimp, Fenneropenaeus chinensis (Osbeck), with initial body weight of 0.36 ± 0.04 g were studied at average temperature 25, 28 and 31 °C from May to July, 2000. Among four diel different fluctuation amplitudes of ± 1, ± 2, ± 3 and ± 4°C, the growth rate of shrimp at 25 ± 2, 25 ± 3, 28 ± 2 and 31 ± 1 °C were significantly higher than those at corresponding constant temperatures of 25, 28 and 31 °C, respectively, while growth rate at 31 ± 4 °C was significantly lower than at 31 °C. There is a trend that the optimal thermal amplitude for shrimp growth decreased with the increase of average temperature in the present study. The growth rate of Chinese shrimp was a quadratic function of the thermal amplitude at the same average temperature. Such a growth model may be described by$G={\beta }_0+{\beta }_1\left(\mathrm{TA}\right)+{\beta }_2{\left(\mathrm{TA}\right)}^2$where G represents the specific growth rate on a 33-day basis, TA is thermal amplitude in degree Celsius, β₀ is intercept on G axis, and β₁ and β₂ are the regression coefficients. The optimal thermal amplitude for the growth of shrimp at sizes of this experiment at average temperature of 25, 28 and 31 °C was estimated to be ± 2.0, ± 2.2 and ± 1.4 °C, respectively. The changes of food conversion efficiency were similar to the growth rate, while the trends of food consumption of shrimp between fluctuating temperature and constant temperature were variable at different average temperatures. There was no significant difference in apparent digestibility coefficient between diel fluctuating temperatures and corresponding constant temperatures. Therefore, more food consumption, high food conversion efficiency and more energy partitioned into growth might account for the enhancement in the growth of shrimp at the diel fluctuating temperatures in the present study.     

Growth of the green mussel, perna viridis L., in a sea water circulating system

Growth of the green mussel, P. viridis L., was studied in a sea water circulating system for 12 months. The maximum growth rate was recorded during March–May, coinciding with the maximum abundance of phytoplankton. The other hydrological parameters did not show any marked correlation with growth rate, which was chiefly influenced by the availability of food. A significant relationship was noted between the shell length and total weight of the mussel, i.e.

$\text{W = 3.7522 L}{}^{1.3007}$

The maximum growth rate (91.62%) was recorded at an early stage and was followed by a sharp decline to 5.78%. The growth pattern of the mussel fitted well with the von Bertalanffy growth equation:

$\text{Lt = 110 (1?e}{}^{\mathrm{?0.1124\; (t+0.0889)}}\text{)}$

     

Botulism in juvenile coho salmon (Oncorhynchus kisutch) in the United States

Botulism type E was first recognized as a major cause of fish mortality in the United States in 1979. This disease caused an estimated loss of $\text{1}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ million juvenile salmon reared in earth-bottom ponds during the summer and fall of 1979 and 1980. The botulism outbreaks, preliminary laboratory results of experimental botulism, and precautions to be taken by fish farm employees are discussed.     

Involvement of steroid hormones in the preovulatory gonadotropin surge in female goldfish

Goldfish,Carassius auratus, spawn several times within a spawning season. A gonadotropin (GtH) surge occurs at the time of ovulation in this cyprinid species. This ovulatory GtH surge mediates the processes of final oocyte maturation and ovulation, and occurs at the end of each spawning cycle. Within a cycle, there is a shift in the predominant plasma steroid from estradiol to testosterone, and finally 17α, 20β-dihydroxy-4-pregnen-3-one at the time of the ovulatory GtH surge. High levels of testosterone were always observed before ovulation. When ovariectomized or sexually regressed female goldfish were implanted with testosterone, they exhibited a GtH surge which was similar to those normally observed at ovulation. These results strongly suggest that elevated plasma testosterone is an important physiological requirement for the occurrence of the GtH surge.     

Cold tolerance at three salinities in post-larval prawns,Macrobrachium rosenbergii (De Man)

Post-larval Macrobrachium rosenbergii acclimated to 27, 22, or 16°C and 5, 8, or 14 ‰ were temperature-shocked to 16°C or $\text{13°}\text{16°}\text{C}$ for 1 week. Survival was significantly better in animals acclimated to 22°C or below. Salinity had no significant effect on survival. Growth of post-larvae which had been maintained at 16°C or below for 3 weeks was followed for 1 month at 27°C; it was not significantly different from that of 27°C controls. Slower growth was observed in the 14‰ prawns. These data indicate that post-larvae stocked into cool ponds from warm hatcheries might benefit from pre-acclimation to lower temperatures. Exposure to cold does not adversely affect later growth.     

Involvement of protein kinase C in the modulation of gonadotropin and growth hormone secretion from dispersed goldfish pituitary cells

It has been established that secretion of gonadotropin (GtH) and growth hormone (GH) release in goldfish are both stimulated by GtH-releasing hormone (GnRH); in addition GtH secretion is inhibited by dopamine D₂ mechanisms. In the present study, depletion of protein kinase C (PKC) in goldfish pituitary cells reduced the GtH and GH responses to GnRH and an activator of PKC in static culture. In perifusion studies, GtH released in response to sGnRH analog was greatly attenuated in PKC-depleted cells, however, hormone responses to forskolin were enhanced. Stimulation of dopamine D₂ receptors reduced the GtH, but not the GH, responses elicited by PKC activators. These results indicate that PKC participates in the GtH and GH responses to natural neuroendocrine regulators in the goldfish.

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Résumé Il a été établi que chez le poisson rouge, les sécrétions de gonadotropine (GtH) et d'hormone de croissance (GH) sont toutes les deux stimulées par la gonadolibérine (GnRH); de plus, la sécrétion de GtH est inhibée par des mécanismes dopaminergiques de type D₂. Dans le présent travail, la déplétion de la teneur en protéine kinase C (PKC) dans des cellules hypophysaires de poisson rouge réduit les résponses en GtH et GH au GnRH et à un activateur de la PKC de cellules maintenues en incubation statique. Dans des cellules maintenues en périfusion et soumises à une déplétion en PKC, la GtH libérée en réponse à un analogue du sGnRH est fortement diminuée, cependent les réponses hormonales à la forskoline sont augmentées. La stimulation des récepteurs dopaminergiques D₂ réduit, dans le cas d'action d'activateur de la PKC, la réponse en GtH mais pas en GH. Ces résultats indiquent que la PKC est impliquée dans les mécanismes de régulation de GtH et GH par des facteurs neuroendocriniens naturels.

     

Aquaculture development in less developed countries: Social,economic and political problems: Leah J. Smith and Susan Peterson. Bowker Publishing Company,Essex, U.K., 1982. 152 pp., US$ 29.50. ISBN 0-86531-235-4

Oxygen consumption and ammonia production in elvers of varying growth rates were studied. The allometric equation describing the relationship between oxygen consumption and weight is y =00.638 x^0,525, where y is the oxygen consumption (mg/h) and x is the mass (g). The weight specific allometric equation for the relationship between ammonia excretion and weight is $\text{y}\text{x}\text{= 0.0129 x}{}^{\mathrm{0,465}}$. Slow growing elvers were found to have higher respiratory rates (0.737 mg O₂ h^?1 g^?1) than would be expected for their size.     

Selection experiments with salmon: IV. Growth of Atlantic salmon during two years in the sea

Brood stock of Atlantic salmon were sampled from 37 rivers or riversystems (strains) for three consecutive years. Each strain was represented by several full- and half-sib families. During the freshwater period each full-sib family was reared separately and each group was given as equal environmental conditions as possible. Fingerlings large enough to become 1-year-old smolt were freeze-branded and smolts from the different strains were sampled and transported to five salmon farms along the Norwegian coast. This paper deals with body weight and length of Atlantic salmon after a growth period of 2 years in the sea.Significant differences between strains were found for all three year classes. The interaction farm × strain was significant but accounted for only a small part of the total variation. It is concluded that genotype × environment interaction can be ignored when planning a selection programme for Altantic salmon for Norwegian farming conditions. A significant interaction sire × dam was found for the 1972 year-class, implying the presence of non-additive genetic variation. The heritabilities for body weight and length estimated from sire components (year-class 1973 and 1974) were quite high: 0.31 and 0.28, respectively. Genetic correlations between body weight and length were close to unity. The heritabilities for condition factor ($\text{K=}\text{weight in g}\text{(length in cm)}{}^3\text{·100}$ were small and none of the sire components were significant. It is concluded that the combination of weight and length used in calculating the K-factor has minor genetic basis.Genetic variation in body weight of Atlantic salmon is high, and about three times as high as for body length.     

Broken eggs as a cause of infertility of coho salmon gametes

Egg content originating from ruptured ova progressively reduced the success of fertilization in coho salmon (Oncorhynchus kisutch) eggs. The salmon egg differs in ionic composition from the ovarian fluid in exhibiting higher K⁺ and Mg²⁺ and lower Na⁺ concentrations. Normal ovarian fluid induced spermatozoan motility whereas ovarian fluid contaminated with egg content progressively lost the ability to induce motility. Loss of motility was related to decreasing $\text{Na}{}^{\mathrm{+}}\text{K}{}^{\mathrm{+}}$ ratios in the ovarian fluid, indicating that reduced fertility may be caused by inactivation of sperm cells in the insemination medium. Removal of contaminated ovarian fluid by rinsing ova in isotonic media induced spermatozoan motility and restored fertility completely. The use of an isotonic NaHCO₃ solution for rinsing of ova is suggested as a routine procedure for artificial insemination in salmonids where the presence of broken eggs is suspected.