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.     

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.     

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.     

The effect of temperature on the clearance of intraperitoneally-injected gonadotropin in the goldfish Carassius auratus

The serum half-disappearance time ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$), metabolic clearance rate and volume of distribution of intraperitoneally administered carp gonadotropin (cGtH) and endogenous GtH levels were determined in sexually mature male and female goldfish, Carassius auratus maintained at 12 ± 1°C or 20 ± 1°C. The results indicated that the rate of serum uptake of the injected cGtH from the peritoneal cavity was greater at 20°C than at 12°C in sexually mature male goldfish. Although increased endogenous serum GtH levels and decreased values of serum $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ were associated with the elevated temperature, there was no difference in any of the parameters between sexually mature male and female goldfish acclimated to 12°C.     

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:

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

     

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.     

Secretion of hatching enzyme and its proteolytic activity in coregoninae (Coregonus albula L andC. lavaretus L) embryos

After the electrial stimulation Coregoninae embryos secreted the hatching enzyme (chorionase) within 0.1–0.5 h, and the dissolution of their chorions lasted 1.2–2.0 h, depending on embryo's developmental stage (DS 13 or DS 14) and water temperature (5.2 or 9.6–9.8°C).Crude chorionase (hatching liquid) ofCoregonus albula andC. lavaretus was collected in large quantities by means of the electric stimulation of eggs. In both species the temperature optimum of proteolytic activity of the crude chorionasc was 30°C; the activity was lost at temperatures < 3-2°C and > 35–40°C. The maximal proteolytic activity was observed at pH 8.5; a rapid decrease in enzyme activity was evident at pH < 7.0, and the activity was zero at pH 6.The temperature-activity curve of chorionase may reflect the adaptation of Coregoninae to hatching immediately after the ice cover recedes from lakes, whereas the rapid decrease of enzyme activity at pH 7 -pH 6 can affect adversely the process of hatching in acidified lakes.     

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.     

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.     

Incubation experimentale et developpement embryonnaire de la daurade royale, Sparus aurata (L.), a differentes temperaturesIncubation and embryonic development of gilthead bream, Sparus aurata (L.), at a range of temperatures

Eggs of raised gilthead bream, Sparus aurata (L.), were incubated to hatching at various temperatures ranging from 7.7°C to 26.3°C. For four stages of development, the relationship between temperature and incubation time is given. Time from fertilization to hatching varies from 135 h at 11°C to 40 h at 21.3°C. In our experiments no egg hatched below 11°C or above 22°C. The highest hatching rate and the lowest rate of larval abnormalities were both observed at 14.5°C which is also the spawning temperature.     

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.     

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.     

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.     

Effect of temperature on energetic demands during the last stages of embryonic development and early life of Octopus vulgaris (Cuvier, 1797) paralarvae

This study describes the effect of seasonal average temperatures (14 and 18°C) in the Ría of Vigo, on the utilization of external yolk over the last five Naef stages of development (XV–XX) for Octopus vulgaris embryos. Also, the transference of the outer yolk to the inner yolk sac, and its use during embryonic development and early life by O. vulgaris paralarvae. Temperature had a marked effect on embryonic development, except during stages XV–XIX (until the second inversion) where development time was the same (14 days), regardless of temperature. There were no significant differences in outer yolk decrease between consecutive Naef stages at 14°C and 18°C. Contrary, significant differences at all Naef stages from XV to XIX (both, with or without outer yolk) were observed for inner yolk between temperatures. A higher accumulation of inner yolk in embryos at 14°C was observed, due to lower yolk consumption. Paralarvae incubated at both temperatures were maintained independently at starvation during 4 days. At 18°C, a reduced accumulation of inner yolk, especially during Naef stage XIX, was observed. In 24 h old paralarvae, there was already significant higher inner yolk content at 14°C than at 18°C. Unfed paralarvae at 18°C lost weight faster than those at 14°C, due to higher energetic requirements. Finally, from these results, we propose a paralarvae rearing protocol during the first days after hatching and during the last five Naef stage (XV–XX) at lower temperatures, since the energy requirements are lower during the initial maturation stage.     

The effects of constant and oscillating temperature on embryonic development and early larval morphology in longfin yellowtail (Seriola rivoliana Valenciennes)

Constant and oscillating egg incubation temperatures on embryonic development and early larval morphology were studied in longfin yellowtail (Seriola rivoliana Valenciennes). We investigated the effects of constant temperatures from 16 to 32°C on embryo development and larval morphology at hatch, and whether oscillating temperature during embryogenesis could lead to larval morphological variations. After hatching, larval morphology and development during yolk sac (YS) utilization were examined in larvae at constant temperatures and larvae at 25°C that had oscillating temperature during egg incubation. Hatching rates were > 75%, only decreasing to ~ 50% at 30°C. At constant temperatures, the largest larvae occurred at 22 and 24°C. The oscillating temperature did not affect the timing of embryo development but resulted in larger and smaller larvae with a smaller and bigger YS, respectively, with a similar hatching time. Therefore, a growth response occurred in embryos during a window of development before hatching, depending on the adaptive response to temperature (spawn‐specific). After hatching, most of the YS was absorbed within 24 hr in all treatments, and the growth of the larval head was a priority with an optimal development at 26°C. There was compensatory growth in smaller larvae resulting in similar sizes after YS utilization, but larvae showed variations in body structure that could be important in further aquaculture research.