Growth and survival of first-feeding spotted wolffish (Anarhichas minor Olafsen) at various temperature regimes

In order to define temperature regimes that could benefit successful production of spotted wolffish (Anarhichas minor) juveniles, experiments with offspring from two different females were carried out. The larvae were fed a new formulated feed or a commercial start‐feed for marine fish, both of which have given high survival rates. In the first experiment newly hatched larvae were fed at constant 6 °C, 8 °C, 10 °C and 12 °C as well as at ambient seawater temperature (2.9–4.5 °C) during 63 days. High survival, 90% to 96%, was registered at ambient and most constant temperature regimes, whereas in the 12 °C groups survival was reduced to 80%. Growth rate (SGR) was very low, 1.8% day^?1, at the low ambient temperatures. Growth rate was positively correlated with temperature and varied between 3.1% day^?1 to 4.7% day^?1, from 6 °C to 12 °C. In the second experiment, set up to include potential detrimental temperatures and study beneficial effects of a more restricted, elevated first‐feeding temperature regime, the larvae were fed at constant 8 °C, 10 °C, 12 °C, 14 °C and 16 °C until 30 days post hatch, followed by constant 8 °C for the next 33 days. In this experiment, low survival, 25% and 2.0%, was registered at 63 days post hatch when larvae were reared initially at 14 °C and 16 °C respectively. The survival of the larvae at the other temperature regimes varied from 47% to 64%, highest survival rate (64%) was found at 8 °C. The lowest specific growth rate, 2.6% day^?1, was noted in the 16 °C group. At constant 8 °C to 14 °C (regulated to 8 °C), the SGR varied from 4.45% day^?1 to 5.13% day^?1. The larvae grew faster in the experiment when initially comparable temperatures (8 °C, 10 °C and 12 °C) were regulated to constant 8 °C after 30 days compared with the first experiment where feeding was carried out at the same constant temperatures (8 °C, 10 °C and 12 °C) during the whole experimental period.     

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.     

The effect of temperature on early development of barbel Barbus barbus (L.)

The rate of swelling of barbel Barbus barbus (L.) eggs and of embryonic development increased with temperature (from 12 to 22°C). Survival of embryos decreased during the embryonic development and the highest mortality at each developmental stage occurred at 12 and 22°C. Body malformations in embryos during cleavage and organogenesis were the most frequent at 12, 14 and 22°C. During the embryogenesis, three types of embryonic body malformations were observed: yolk sac oedema, spine curvature and shortening of body. At all temperatures, most of larvae hatched with tail first but at 12 and 22°C significantly more larvae hatched with yolk sac compared to the other temperatures. The highest percentage of normal viable larvae was obtained at 14 and 18°C. Larval malformations and dead larvae were significantly most frequent at 12 and 22°C compared to the other groups. At all temperatures, spine curvatures and yolk sac deformation were the most frequent types of larval deformations.     

Effect of temperature increase on the embryonic development of Patagonian red octopus Enteroctopus megalocyathus in controlled culture

One of the major problems involved in the controlled cultivation of Patagonian red octopus (Enteroctopus megalocyathus) is its long embryonic period ranging between 150–176 days, after which the hatching of planktonic paralarvae is achieved. The effect of temperature on the incubation of E. megalocyathus eggs was studied with the aim of establishing if a temperature higher than 12°C is effective to accelerate the embryonic development without altering their morphological and physiological conditions. Fertilized eggs obtained under controlled conditions at 11°C ± 0.1 were randomly distributed in 12 water baths of 30 L at 4 temperatures: 12, 14, 15 and 16°C ± 0.1°C. The experiment lasted until egg hatching occurred.The embryo growth rate was accelerated at 15–16°C, so the time spent in embryonic development can be reduced in 15% when compared with embryo development obtained from eggs incubated at 12°C. The embryos showed no significant differences in the final survival and were morphometrically similar in all stages of development at all temperatures. The increase in temperature from 12 to 16°C, even if it allowed a better growth, had high metabolic costs for embryos of E. megalocyathus. The activities of lipases and proteases were affected by interaction between temperature and the embryo stage, with high lipase activity observed in embryos of stage XV incubated at high temperatures and the highest levels of trypsin and chymotrypsin in stage XX at 14°C. The results suggest that 15°C could be the limit temperature to increase growth.     

Effect of different chilling rates for cold anaesthetization of Penaeus monodon (Fabricius) on the survival, duration and sensory quality under live storage in chilled sawdust

The present work was carried out with a view of determining the chilling rates for cold anaesthetization and live storage of Penaeus monodon (Fabricius) in chilled sawdust, for live transportation. Three chilling rates of 1.38 ± 0.16 °C h^?1 within 8 h (slow), 2.76 ± 0.32 °C h^?1 within 4 h (moderate) and 5.52 ± 0.64 °C h^?1 within 2 h (fast) were tested to cold anaesthetize 144 farm‐raised P. monodon (22–25 g) in each chilling rate at 15 g L^?1 salinity, from 25 °C down to 14 ± 1 °C in plastic net boxes kept in a refrigerated chilling tank provided with aeration. Eight cold‐anaesthetized shrimps subjected to each chilling rate were packed in an insulated cardboard box (triplicate) between two layers of moist and chilled (2–3 °C) sawdust, and kept inside a chilled storage cabinet at 14 ± 1 °C for durations of 16, 20, 24, 28, 32 and 36 h. Survival was determined by revitalizing the shrimps in aerated water with an initial temperature of 20 °C, which was raised to 28 ± 1 °C at 2.7 °C h^?1 within 3 h. Statistically valid, safe durations for obtaining 100% survival were 22.9 ± 1.1, 19.1 ± 0.4 and 14.6 ± 1.1 h, using probit analysis at the slow, moderate and fast chilling rates respectively. The weight loss (1.5–8.8%) due to cold anaesthetization and subsequent revitalization of the packed shrimp was insignificant. Sensory evaluation showed significant improvement in general appearance, and also in colour as well as in flavour of the meat when compared with that of the freshly harvested dead shrimps. The texture as well as odour of the raw and cooked meat between treated and untreated shrimps was unaffected. The effects of chilling rates and shipping durations on sensory quality were insignificant. One hundred per cent survival was obtained for 24, 20 and 16 h for the slow, moderate and fast chilling rates respectively. Percentage survival of the shrimps at different durations was significantly different among the chilling rates, but pair‐wise comparison revealed that the slow and moderate chilling rates were identical. Hence, the moderate chilling rate, which took only 4 h, can be considered the optimum, though the choice of different chilling rates depends on the duration of live storage desired.     

Influence of incubation temperature on body movements of Atlantic cod (Gadus morhua L.) embryos and on size at hatch

Body movements of cod (Gadus morhua L.) embryos reared from fertilization to hatch at 5.4°C were observed at various stages of development and at six experimental temperatures ranging from 0–10°C. Frequency of cod embryo body movements increased from zero at 42 degree‐days post fertilization to maximal at 73–82 degree‐days (1 or 2 days prior to hatch). Embryos were most active at 2°C (mean of 5.5 movements per 10 min), with activity declining to less than 1/10 min at 8–10°C. Lengths of hatched cod larvae reared at a series of constant temperatures (from 4–10°C) from fertilization to hatch were greater at lower incubation temperatures. Incubation temperatures of 2–4°C were found to be optimal for incubation of cod eggs.     

Motoricity of Atlantic salmon embryos (Salmo salar L.) at different temperatures

Atlantic salmon eggs were fertilized and incubated in two temperature series at 3 and 8°C. Four motor criteria (heart rate, embryo motion, motion of the pectorals and motion of the mouth-gill apparatus) and oxygen consumption at different stages of embryogenesis were studied. At certain intervals the temperature was changed rapidly (within 30 min) to 3, 6, 8, 10, 12, 14 or 16°C and the detectable changes in the above motor criteria were recorded. Heart rate and embryo motion were the first recognizable motor components. The heart responded particularly sensitively to temperature shock with a change in heart rate, whereas temperature changes were not clearly reflected in embryo motion because space within the egg membrane was restricted owing to embryonal growth. Motion of the pectorals and mouth-gill apparatus did not start until shortly before hatching and achieved maximal values at 8–10°C. Pulse rates for all of the motor criteria except embryo motion were distinctly higher for eggs incubated at 8°C than for those incubated at 3°C.     

The influence of rearing temperature on early development and growth of spotted wolffish Anarhichas minor (Olafsen)

Temperature influenced the developmental rate, survival and early growth of eggs and embryos of spotted wolffish, Anarhichas minor (Olafsen), an interesting candidate for cold water cultivation. The total incubation period decreased from 220 days at 4 °C (880 daydegrees), to 177 days at 6 °C (1062 daydegrees) and 150 days at 8 °C (1200 daydegrees) in these experiments. The proportion of normal embryos and survival of eggs until hatching were highest when the eggs were incubated at 6 °C. During the incubation period, the embryo and yolk sac size at 280 daydegrees was not significantly different but at 850 daydegrees the embryo size was inversely related to temperature and the remaining yolk sac size positively correlated with the incubation temperature. The transformation of yolk to body mass during incubation appeared to be most efficient at 4 °C, and the embryos hatched with a larger visible yolk sac at 6 and 8 °C. The largest larvae (wet‐weight) hatched from the largest eggs and the egg groups incubated at the lowest temperature (4 °C). There was no effect of temperature on meristic characters. During 6 weeks post‐hatching, all larvae from the three temperature groups were fed formulated dry feed in excess at 8 °C in low water‐level raceway systems. During startfeeding, the larvae from eggs incubated at the lowest temperature (4 °C) showed the highest growth rates (SGR). Best survival of larvae was noted among batches incubated at 6 °C.     

First feeding of burbot, Lota lota (Gadidae, Teleostei) larvae under different temperature and light conditions

The burbot (Lota lota) is the only fresh water member of the cod family, Gadidae, and is adapted to cold waters. The effects of temperature and light on the growth and survival of burbot larvae were investigated under hatchery conditions. Three temperature regimes (12, 16 and 20°C) were applied under continuous light and darkness during the experiment. Rotifer, Brachionus calyciflorus (L.) were fed to the larvae in the first 10 days and the diet was then replaced with Artemia nauplii. At the end of the feeding stage with rotifer, growth in terms of the total length and wet weight were larger at higher temperatures under continuous light. At day 10, survival rates of the fish held at 12°C under continuous light and darkness regime were higher than those held at 16°C and 20°C kept under the same conditions. From day 10 onwards, larval growth improved remarkably after changing the live food from rotifer to Artemia in all treatments. At the end of the study, the highest survival rate was recorded among the larvae held at 12°C exposed to continuous light. Under light condition, the temperature of 20°C did not result in an improved larval growth compared with 16°C. This may indicate that high temperature and continuous light are not beneficial for larval growth and survival when they reach older stage of development. The results indicate a significant interaction for the combination of temperature, light and time with respect to survival and wet weight, making unambiguous interpretation of the main effects difficult.     

Live transportation of Macrobrachium rosenbergii (De Man) in chilled sawdust

Three cooling rates of 1.26±0.09°C h^?1 within 8 h (slow, T₁), 2.52±0.18°C h^?1 within 4 h (moderate, T₂) and 5.04±0.36°C h^?1 within 2 h (fast, T₃) were tested to cold‐anaesthetize farm raised Macrobrachium rosenbergii (De Man) (45–52 g) in each case from 25°C down to 15±1°C in a refrigerated chilling tank, provided with aeration. The cold‐anaesthetized prawns subjected to each chilling rate were packed in an insulated cardboard box (triplicate) between two layers of moist and chilled (2–3°C) sawdust, and kept inside a chilled storage cabinet at 15±1°C, for set durations of 6, 9, 12, 15 and 18 h. Survival was determined by revitalizing the prawns in aerated water with an initial temperature of 20°C, which was raised to 29±1°C within 3 h. The experiment was repeated using berried females acclimated to brackishwater of 12 g L^?1 salinity and the percentage survival recorded after live storage for durations ranging from 6 to 24 h at intervals of 3 h. Statistically valid safe durations for obtaining 100% survival of the cold anaesthetized and live stored prawns were determined using probit analysis at the three chilling rates tested, and were found to be 7.39, 6.98 and 4.54 h in the case of adult prawns, and 7.87, 8.17 and 6.43 h for berried females for T₁, T₂ and T₃ respectively. For practical purposes, the durations that yielded 95% survival rates were computed to be 16.47, 12.14 and 8.35 h in the case of adult prawns and 18.49, 19.02 and 11.11 h for berried females for T₁, T₂, and T₃ respectively. The berried prawns revitalized after live storage were incubated in tanks and the zoea larvae reared up to postlarvae (PL‐5), and compared against a control. No significant difference was found in larval hatch fecundity, survival rate and the production of PL L^?1 between the treatment and control, indicating that the method of cold anaesthetization and live storage of berried prawns could be used for successful transportation of broodstock.     

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.     

西昌白鱼雅砻亚种胚胎发育研究

西昌白鱼(Anabarilius liui)为中国特有种,隶属鲌亚科,白鱼属,共记载有16种和亚种,大多分布于云南,在四川省仅分布于凉山州,共有2个种和亚种。西昌白鱼(雅砻亚种)(A. liui yalonggensis)是雅砻江特有种,是增殖放流品种之一,但自命名后多次调查均未采集到,资源量情况不容乐观。通过人工干法授精获得西昌白鱼(雅砻亚种)受精卵,在恒定水温(14.4 0.8)℃条件下进行孵化,对其胚胎的发育过程进行了观察和描述,旨在为该鱼的科学养护提供技术支撑。结果表明：西昌白鱼成熟卵(n=10)卵径为(1.83 0.15)mm,沉性,粘性,接近无色透明,吸水充分膨胀后卵径为(2.53 0.07)mm。在波动水温“昼(21.5 1.7)℃-夜(15.0 1.2)℃”、恒定水温(23.5 2.2)℃条件下胚胎均能不能成功孵化,胚胎均发育至肌肉效应期即全部死亡。在水温(14.4 0.8)℃的条件下,胚胎受精后1h30min胚盘隆起,14h55min和35h45min进入囊胚期和原肠胚期,46h5min胚孔封闭,158h35min开始出膜。胚胎发育积温为2284.4℃?h。初孵仔鱼(n=10)全长(5.77 0.24)mm。西昌白鱼(雅砻亚种)胚胎较鲌亚科其他种类,具有较大的卵径、脊索形成期在胚孔封闭期之前等特征,是其对雅砻江环境的一种适应和进化。     

Influence of stocking density and temperature on early development and survival of the purple sea urchin,Strongylocentrotus purpuratus (Stimpson, 1857)

We evaluated the effect of four densities (940, 1880, 3760, 7520 eggs cm^?2 and 0.5, 1, 2, 4 ind mL^?1 of embryos and larvae, respectively) and four temperatures (8, 11, 14, 17°C) on early growth and survival of the sea urchin Strongylocentrotus purpuratus. Prism‐stage length was significantly greater in embryos initially held at 940 and 1880 eggs cm^?2 than in those held at 3760 and 7520 eggs cm^?2. Larvae grew significantly faster and had significantly greater survival when reared at 0.5 or 1 ind mL^?1 than when held at 2 or 4 ind mL^?1. Embryos had greater survival at 11 and 14°C than at 8 and 17°C, whereas embryo length was significantly smaller at 8°C than at 11, 14 or 17°C. Larvae grew significantly slower at 8°C than at 11, 14 or 17°C, whereas survival was significantly reduced at 8 and 17°C compared with 11 and 14°C. Per cent survival from prism to metamorphic competency in the best treatments was 48.9 ± 2.2% and 50.0 ± 3.6% (mean ± SE) for the 1 ind mL^?1 and 11°C treatments, respectively. On the basis of these results, for rearing of S. purpuratus under static conditions, we recommend that fertilized eggs and larvae be held at ≤1880 eggs cm^?2 and ≤1 ind mL^?1, respectively, and at 11–14°C.     

Investigations on the effect of formalin and iodophor on embryo and larvae development in pikeperch,Sander lucioperca

ABSTRACT

An experiment was conducted to evaluate the effects of incubating pikeperch, Sander lucioperca, eggs in formalin and iodophor solutions for 15 min on embryo survival, the hatching rate, as well as on the rate of misshaped larvae, in order to develop methods for egg surface disinfection. Embryos in the morula stage, in the epiboly stage, and at the beginning of heart beat and blood circulation tolerated formalin concentrations up to 1,500 ppm for 15 min. However, they were very susceptible to iodophor treatment, as >0.1% iodophor solution (=13 ppm active iodine) significantly decreased the percentage of ready-to-hatch embryos and the percentage of hatched larvae. These data of this study recommend the use of formalin at a concentration of up to 1,500 ppm to disinfect pikeperch eggs.     

Development of the common dentex (Dentex dentex) eggs in relation to temperature

Embryonic development of common dentex (Dentex dentex) was investigated at nine different constant water temperatures (8°C, 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C and 24°C). The observed effects were compared using of regression analysis. Constant water temperatures between 12°C and 18°C were found to support successful embryonic development. A negative relationship between the rate of embryonic development and incubation temperature was observed. While embryonic development was completed within this range (12°C–18°C), there was no cell division at water temperatures of 8°C and 24°C. Total mortalities were observed at the 128 cleavage stage at a temperature of 10°C, and after the beginning of gastrulation at 20°C and 22°C.     

Induced out-of-season spawning of the mud crab, Scylla paramamosain (Estampador) and effects of temperature on embryo development

Treated with combined bilateral eyestalk ablation and maintenance of water temperature at 22.5±1.5 °C, mud crab Scylla paramamosain females with mature ovaries were induced to produce eggs outside the natural spawning season in subtropical southern China. Newly extruded eggs from a crab were incubated in vitro at 10, 15, 20, 25, 27, 30, 35 °C, respectively, and the embryonic development was closely monitored. Abnormal cell division was observed at temperatures 10 and 35 °C. At 15 °C, development remained at the gastrula stage by day 32 post‐spawn, at which time the experiment was terminated. Hatching of in vitro incubated eggs occurred between 20 and 30 °C. An increase in incubation temperature from 20 to 25 °C reduced the incubation duration by 14 days, 2.6 times of that measured for a similar 5 °C increase from 25 to 30 °C. Embryonic development of S. paramamosain was divided into stage 0–10, and the duration of each stage was recorded for each incubation temperature. The information obtained allows accurate prediction of hatching time of female crabs incubated under variable temperatures. Larvae hatched from in vitro incubated eggs were reared to reach first juvenile crab stage and their dry weights were similar to those of larvae hatched naturally.     

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.     

Effect of drying on the viability of the probiotic bacterium Lactobacillus plantarum Lab9 (CPQBA 144‐09 DRM 03) impregnated in the feed for tilapia (Oreochromis sp.)

Drying experiments were conducted at different temperatures and air flux velocities to determine the proper drying conditions for reducing moisture in commercial fish feed impregnated with probiotic lactic acid bacteria and to assess the effect on bacteria viability over time. At temperatures of 45°C, the drying time was shorter, without the air flux velocity under study having a relevant influence. The drying conditions influenced the viability of the bacteria in the feed; the least loss of viability was obtained with a velocity of 0.8 m s^?1 and a temperature of 45°C during 15 min. Using these drying conditions, 5 kg of feed was dried and stored for a month at temperature of 26°C and relative humidity of 75%. The viability of the bacteria and the moisture of the feed were measured every 3 days during the storage period. Loss of viability followed first order kinetics, with a constant k of 0.112 days^?1. Thus, the viability of the bacteria in the feed is less than 10⁶ CFU g^?1 after 43 days.     

Effects of fertilization and incubation factors on the quality and yield of scallop, Pecten fumatus Reeve, larvae

Variable quality and yield (percentage development from eggs) D-veligers of the scallop, Pecten fumatus Reeve, prompted assessment of fertilization and incubation protocols. Various sperm to egg ratios were tested on eggs suspended in sea water at different densities. Ratios of 1000:1 led to the highest D-veliger yield when eggs were incubated in suspension at one per millilitre. With increasing egg densities, the addition of 1000 sperm per egg led to increasing average numbers of sperm visible at the periphery of each egg, indicating that fewer sperm were necessary for fertilization at higher egg densities. The time period and temperature over which released gametes were stored before fertilization were also found to significantly affect D-veliger yield. Decreasing gamete storage temperature from 26 to 14^oC increased D-veliger yield, as did a reduction in the gamete storage period from 6 to 1 h. The incubation of embryos at densities in the 5-50 ml^-1 range did not affect D-veliger yield. A significant increase in total bacterial counts in the culture water occurred with increasing embryo stocking densities. However, presumptive Vibrionaceae counts did not increase significantly with increasing embryo stocking densities. In a comparison of the viability of self- and cross-fertilized embryos and larvae, fewer self-fertilized embryos developed to D-veliger stage; however, percentage survival, although highly variable, did not differ significantly in subsequent larval rearing. Cross-fertilized larvae had attained a significantly larger size by day 7.     

Long-term cryopreservation of spermatophore of the giant freshwater prawn, Macrobrachium rosenbergii (de Man)

Long‐term cryopreservation of the giant freshwater prawn, Macrobrachium rosenbergii, spermatophores using glycerol (Gly) and ethylene glycol (EG) as cryoprotective agents (CPAs) was studied. The tolerance of sperm to cryopreservation was evaluated on the basis of sperm survival and fertilizing ability. The survival of the sperm was determined by trypan blue staining, while the fertilizing ability was assessed from artificial insemination of the cryopreserved spermatophores. The rates of embryo survival on day 5 after spawning and of spermatophores capable of producing embryos survived to hatching were determined. Storage of spermatophores at ?20°C without CPA for a short period of up of 1–5 days decreased the sperm survival significantly and did not preserve fertilizing ability. Preservation at ?20°C in the presence of 10% or 20% Gly or of 10% or 20% EG offered a simple and efficient short‐term storage up to 10 days. For a long‐term storage, cryopreservation in the presence of 20% EG at ?196°C was more efficient than at ?20°C. High sperm survival rates and high fertilizing ability were recorded from those cryopreserved at ?196°C for up to 150 days. High sperm survival rates with moderate levels of fertilizing ability were obtained from those cryopreserved at ?20°C for not more than 30 days. The results indicate that preservation at ?196°C with 20% EG is a suitable procedure for long‐term storage of the giant freshwater prawn spermatophores.