Stimulation of ovarian growth by methyl farnesoate and eyestalk ablation in penaeoidean model shrimp,Sicyonia ingentis Burkenroad, 1938

The effect of methyl farnesoate (MF) administration on the vitellogenesis of the penaeoidean shrimp, Sicyonia ingentis, was studied. The short‐ and long‐term treatment effects as well as the effect of two MF injection regimens (0.1 and 1.0 μg MF/injection) were evaluated. The studies were also carried out to understand the pattern of vitellogenesis in eyestalk ablated adult and juvenile shrimps. A combination of endpoints, haemolymph vitellogenin (Vg) levels, gonadosomatic index (GSI) and histology, was used to study the effect of these treatments. The GSI increased in all the MF‐treated shrimp compared with the control shrimps. Although haemolymph Vg levels declined over the experimental period in all the treatments, the Vg levels decreased significantly only in the short‐term treatment with 1.0 μg MF. Similarly, haemolymph protein level also declined over the experimental period in all the treatment groups. However, except in the long‐term treatment with 0.1 μg MF, all treatments showed a significant decrease in haemolymph protein level. Conversely, in all eyestalk ablated adults and juveniles, haemolymph Vg, total protein and GSI increased over the experimental period, all of which were higher than the concurrent control. The discrepancy in the vitellogenic pattern between MF‐treated and eyestalk ablated shrimp was possibly due to the difference in the ovarian phase of the initial control. Although unilateral eyestalk ablation failed to induce vitellogenesis in juveniles, bilateral ablation induced vitellogenesis, which indicates that juveniles are competent to undergo vitellogenesis.     

Histological examination of final oocyte maturation and atresia in wild and domesticated Penaeus monodon (Fabricius) broodstock

Oocyte maturation and gonadosomatic index (GSI) of eyestalk ablated Penaeus monodon females collected from the wild and from two first‐generation domesticated lines were assessed. Frequency and diameter of the different oocytes, and the intensity of oocyte atresia, were compared among groups through histological assessments of the sections of the middle ovarian lobe. Digitized images from ovary sections were used to record the frequency and diameter of different oocyte types. Spawning performance of the three groups were expressed in terms of the percentage of females that spawned at least once (productive females), time from eyestalk ablation to first spawning (latency period) and the number of spawnings per female stocked. Final ovarian maturation was attained in all groups, as indicated by the presence of mature oocytes with cortical rods (cortical oocytes), dark‐green ovarian colour and high GSI values (5.83–6.86%). However, domesticated groups presented significant larger immature oocyte types (previtellogenic and yolky oocytes) and smaller cortical oocytes compared with wild females, indicating a reduced vitellogenic activity during final oocyte maturation. Additionally, the frequency of atresia was comparatively higher for both domesticated groups, which could be related to their inferior spawning performance. The implications of these results on the reproductive potential and development of domesticated P. monodon are discussed.     

日本对虾亲虾的暂养、性腺促熟及幼体培育

本文报告了对日本对虾亲虾进行暂养及切除其单侧眼柄,同时配合适当的生态条件促其性腺成熟等技术措施,并进行了幼体培育。亲虾暂养成活率为83％;促熟率为76.2％;出苗2032.6万尾。     

The cost of early maturation on growth, body condition and somatic lipid content in a lake pumpkinseed (Lepomis gibbosus) population

We investigated the implications of early maturation in a central Ontario population of pumpkinseed (Lepomis gibbosus) by comparing the growth trajectory, body condition, lipid to body weight ratio and past growth history of mature and immature females through the 1992 growing season. Pumpkinseeds were sampled from Beloporine Lake from May 28 to July 24 and on November 20, just prior to freeze-up of the lake. Prior growth history and length at age were determined by backcalculation from scale annuli. Nearly all females age 3 and older had matured in 1992, so we focused on age 2 females (22% mature). Females that matured at age 2 were significantly larger at the end of their first year of life than those that did not mature at age 2, although there was no significant difference between groups in the prior year's growth rate. The mature age 2 females were significantly larger than immatures, at the beginning and end of their third growing season, but not during the June 2 - July 19 breeding season. The condition factor of mature females was higher than that of immature females on all but one collection date. However, the mean somatic lipid-to-body weight ratio was higher in immature females on all sample dates and significantly higher over the grwing season. We conclude that the costs of early maturation include lack of length and weight gain during the breeding season, and loss of stored lipid. The latter may be associated with increased overwinter mortality.     

Successful spawning of cultured Penaeus monodon Fabricius after eyestalk ablation

Preliminary experiments resulted in successful spawning of captive stock of the prawn Penaeus monodon, or “sugpo”, to complete the life cycle and produce a viable F₁ generation of larvae. Gonadal development was induced using eyestalk ablation techniques on sexually mature females. Removal of one eyestalk was found to be sufficient to induce gonadal development, whereas bilateral ablation indirectly resulted in high mortality of the treated females. By comparison, successful spawning had not occurred in unablated animals after 9 months.Fry hatched from wild adult stock and reared to 25-day postlarvae were further impounded in brackishwater experimental ponds and reared for 4 months. A transfer of 1 500 animals were then made to marine pens. After a further 10 months, 600 animals were selected for the experiment; healthy females were ablated unilaterally and placed with 100 males for a further 9 months. Of the remaining 400 specimens, 200 were used as controls and the remainder ablated bilaterally, Seven of the 23-month old females with one eyestalk removed had spawned successfully by January 27, 1976.Egg numbers, hatching rate and larval survival compared favorably with data obtained from females of oceanic origin. It is not known if the success of the experiment was entirely due to the effect of ablation or to the choice of a suitable environment. Work is continuing to induce gonadal development under more closely controlled conditions to overcome the inadequate and unreliable supply of spawners.     

切除单侧眼柄对不同体质量养殖斑节对虾卵巢发育及产卵的影响

在盐度31、水温28~29℃下,进行了4次卵巢诱导试验,研究了切除单侧眼柄对体质量56.4~105.4g的养殖斑节对虾卵巢发育和产卵的影响及卵巢发育、产卵与体质量之间的关系。结果显示,切除单侧眼柄诱导养殖斑节对虾卵巢发育成熟,成功率(y)与雌虾体质量(x)显著相关(P0.05),雌虾体质量越小,诱导成功率越低,回归方程为:y=133.92lnx-535.63(r2=0.9297)。养殖斑节对虾眼柄手术后,最快10d产卵,部分雌虾能重复产卵。产卵量(y)与雌虾体质量(x)显著正相关(P0.05),雌虾体质量越小,产卵量越小,回归方程为:y=122.22lnx-472.2(r2=0.9738)。雌虾累积死亡率、卵子直径和卵子孵化率与雌虾体质量无显著相关性(P0.05)。建议用体质量80g以上的养殖斑节对虾雌虾作为亲虾。     

去眼柄后中华绒螯蟹法呢酸甲基转移酶表达和卵巢发育

为了解甲基法呢酯(methyl farnesoate,MF)在中华绒螯蟹(Eriocheir sinensis)卵巢发育中的调控作用,采用离体方法研究了中华绒螯蟹大颚器(mandibular organ,MO)以及X-器官窦腺复合体(X-organ-sinus gland,XO-SG)对卵巢发育的作用。将MO与离体卵母细胞共培养作为实验组1,将MO和XO-SG与离体卵母细胞共培养作为实验组2,仅添加培养液的卵母细胞作为对照组。实验发现,蟹去眼柄(eyestalk ablation,ESA)后的第1、3、6、14天,同对照组相比,MO对其卵母细胞的发育均有极显著促进作用。ESA处理第6天,MO对卵母细胞发育的促进作用最强。XO-SG能逆转ESA处理后MO对卵巢发育的促进作用(P<0.01)。荧光定量PCR技术检测结果显示,ESA处理后,MO中法呢酸甲基转移酶(farnesoic acid O-methyltransferase,FAMeT)mRNA相对表达量上升。同未去眼柄的对照组相比,第1、3天FAMeT mRNA表达丰度无明显变化(P>0.05),第6、14天表达丰度提高至265%左右(P<0.01)。结果表明,中华绒螯蟹MO功能性物质能够促进卵母细胞发育,且ESA处理后第6天MO生物效应最强。MO中FAMeT mRNA的合成受XO-SG的抑制调节。在离体条件下,中华绒螯蟹XO-SG能够抑制卵母细胞的发育。     

Effect of prepared diet on the induction of precocious maturation in Pleoticus muelleri Bate (Crustacea, Penaeoidea)

Experiments were conducted comparing the reproductive performance of ablated female shrimp Pleoticus muelleri fed either a fresh frozen diet (ND) (clam, prawn, squid) and the same diet supplemented with 15% of an artificial diet (SD) (54% protein, 13% lipid, 7% moisture). The shrimp were maintained in 3500‐L tanks (12 h light‐12 h dark photoperiod, temperature 18–20°C, pH 7, salinity 31 g L^?1, ammonium <0.2 mg L^?1, and sea water exchanged at 100% per day) for 45 days. Significant differences in weight gain were determined between ablated females fed ND (37.2%) and SD (26.4%). No significant differences in the average duration of the intermolt period (19±2 days) were recorded. Females fed SD showed signs of maturation 20 days after ablation, with spawning occurring 1 day later, as long as ablated females fed ND reached maturation 4 weeks after did not occur. The number of eggs per spawn varied from 136 000 to 345 000; the percentage viability ranged between 39.3% and 99.3% with an average of 78.5%. The results indicated that a suitable formulated diet together with eyestalk ablation promotes maturation of P. muelleri in captivity.     

Reproduction of Penaeus kerathurus using eyestalk ablation

In a preliminary experiment on the induction of sexual maturity in Penaeus kerathurus by unilateral eyestalk ablation, spawning was obtained in 94% of the females treated. The time necessary to reach the spawning stage appeared to be closely related to the stage of natural physiological development of the gonads and the length of the photoperiod, the period between ablation and spawning decreasing from 69 days for females treated in November to about 10 days for females treated at the beginning of their natural reproductive period in May/June. Spawning after treatment was repeated up to eight times, sometimes at intervals of less than 10 days, without showing a decrease in the amount of fertile spawn. The mean number of fertile eggs per spawn was 78.400, which is not significantly different from the corresponding mean obtained previously after thermal stimulation of almost mature breeders; the hatching percentage, 67%, was also similar. Often only the anterior and median lobes of the ovaries are included in the spawning process. The discharged spawn is nearly always completely free of matrix material. It is anticipated that induction by eyestalk ablation could allow a considerable extension of the growing season and of the area suitable for culture.     

Unilateral eyestalk ablation improves molting frequency and reproduction in Macrobrachium amazonicum females

This study has investigated the influence of unilateral eyestalk ablation on the survival, molting frequency, fecundity, reproductive output, and fertility of M. amazonicum females. We divided 96 females into with ablation and without ablation groups with six replicates. Water quality, growth, survival rate, intermolt period, molts number, and ovigerous females over a 90-day period were monitored. Unilateral eyestalk ablation reduced intermolt period by 30% and increased molts number, ovigerous females, and reproductive output. Our findings indicate that unilateral eyestalk ablation positively influences reproduction in M. amazonicum and is appropriate for females of this species having a body length of ≥ 70 mm.     

ARTIFICIAL REPRODUCTION OF Penaeus japonicus BATE AS A BASIS FOR THE MASS PRODUCTION OF EGGS AND LARVAE1

Penaeus japonicus Bate is absent on the Italian coasts, but it is considered a very promising species for national aquaculture. To develop the shrimp-culture on a commercial basis, a convenient method for producing eggs and larvae of Penaeus japonicus was studied. A stock of 156 females, age class 1+ and F₃, underwent unilateral eyestalk ablation and they were stocked with males in three plastic tanks (bottom area 14 m²) at a density of 25 individuals/m² and a sex ratio of 1:1. Conditions of environment and management consisted of: temperature 21±3°C; natural light and photoperiod; total exchange of sea water every day; feeding on mussels. A month after eyestalk ablation the females were inspected every 7–10 days; mature females were transferred to the spawning tanks. Females with well developed gonads averaged 25.0% of the population of females at every inspection; 51.3% of spawners were impregnated with spermatophores; others were inseminated artificially by the method of introducing spermatophores into the thelycum. In six inspections (carried out during a period of 89 days), 3,028,525 eggs were released; a female released 17,500 eggs on the average (maximum was 123,000 eggs, minimum 4,340). The mean rate of fertilized eggs was 52.7%—67.7% from naturally inseminated females and 7.5% from the artificially inseminated ones. The mean hatching rate was 30.9%—40.1% from natural insemination and 3.3% from artificial insemination. Total amount of viable nauplii was 820,550.     

Effect of Acclimation Temperature and TemperatureChanges on Molting and Survival of Ablated and Non-ablated Crayfish Orconectes virihs

The effect of acclimation temperatures for producing soft-shell crayfish, and changes upward from acclimation temperature, were evaluated in crayfish Orconectes virilis subjected to either hemilateral or bilateral eyestalk ablation. In each experiment, 60 juvenile O. virilis were reared for 21 d at temperatures ranging from 20 C to 30 C. Equal numbers of male and female crayfish ranging in weight from 5.0 g to 16.0 g were used in each study. In the first three experiments, crayfish were acclimated and maintained at a constant temperature. In the remaining experiments, crayfish were subjected to a step-wise increase in temperature of either 5 or 10 C. Molting was highest in crayfish acclimated to 25 C prior to experimentation at 25 C (experiment 2) and in crayfish acclimated to 14 C prior to experimentation at 20 C (experiment 4). Total molts during these two experiments were 51 (85.0%) and 56 (93.3%), respectively. Bilateral eyestalk ablation resulted in significant reductions in the intermolt period in experiments 1 (acclimation temperature 20 C, experimental temperature 20 C), 3 (acclimation temperature 30 C, experimental temperature 30 C) and 6 (acclimation temperature 15 C, experimental temperature 25 C), while hemilateral eyestalk ablation had no effect on molting when compared to control (non-ablated) crayfish. Bilateral eyestalk ablation resulted in a significant reduction in survival in experiments 5 (acclimation temperature 20 C, experimental temperature 25 C) and 6 (acclimation temperature 15 C, experimental temperature 25 C). Significantly more females molted in one experiment (acclimation temperature 20 C, experimental temperature 25 C), but not in any others. The results of these studies demonstrate that bilateral eyestalk ablation and water temperatures are effective methods of inducing molting in crayfish.     

Effects of temperature on vitellogenesis in Japanese eel Anguilla japonica

ABSTRACT:   Cultured immature female Japanese eels acclimated to sea water at either 10 or 20°C were treated weekly with salmon gonadotropin fraction (sGTH) in order to investigate the effects of water temperature on artificial induction of ovarian maturation. In eels maintained at 20°C, ovulation was induced in 11 of 18 fish during the experimental period of 13 weeks, whereas at 10°C all fish showed a low gonadosomatic index (GSI) at the end of the experiment. Plasma vitellogenin levels were higher in eels kept at 20°C than in eels at 10°C throughout the experiment. However, no significant differences were observed in the plasma testosterone and estradiol-17β levels between groups. Eels pretreated with sGTHs at 10°C for 13 weeks were separated to two different temperature (10 and 20°C) groups, and received the same weekly sGTH injections. In eels transferred to 20°C, plasma vitellogenin levels, GSI and oocyte diameter were increased, but these values were maintained at low levels in eels that remained at 10°C. These results clearly indicate that water temperature is an important factor regulating vitellogenesis in the Japanese eel.     

Effect of dietary sodium chloride acclimation on growth and plasma thyroid hormones in tilapia Oreochromis niloticus (L.) in relation to sex

This trial was conducted in order to test the effect of supplemental dietary sodium chloride on growth and plasma thyroid hormone levels of male and female monosex groups of tilapia Oreochromis niloticus (L.) reared in fresh water and 10‰ brackish water. At the end of the experiment. the gonadal development of females was observed. A high‐salt diet (8% NaCl) was fed to female and male tilapia for a period of 3 weeks. After this time. both groups were transferred directly to fresh water and 10‰ brackish water, and a growth trial was conducted over 90 days. The results indicate that dietary supplementation with NaCl improved the growth of females and males at 30 days, except for females maintained in fresh water. Females reared in 10‰ brackish water showed an increase in growth rates that was accompanied by the highest plasma T3 levels. In contrast, males did not exhibit the same relationship in 10‰ brackish water, showing lower plasma T3 levels than in fresh water. Histological sections of O. niloticus ovaries revealed that female groups contained oocytes at different stages of development. At 90 days, females reared in 10‰ brackish water showed oocytes in maturation, while in fresh water, they showed the highest proportion of vitellogenic oocytes and no mature oocytes. The highest proportion of mature oocytes observed in brackish water was associated with the better growth rate in relation to fresh water. These results confirm that tilapia breed freely in low‐salinity brackish water as well as in fresh water.     

Variation in growth rate,liver weight and body composition at first sexual maturity in rainbow trout

Rainbow trout around 743 g were fed four different diets over an 8-month period. Maturing males grew faster in the period before spawning (Sept.–Dec.) than maturing females, and significantly faster than immature fish. Mature fish stagnated in growth while the immature fish surpassed the growth of mature fish during the spawning season. The condition factor was moderately influenced by the maturation process. In the period before spawning (Sept.–Jan.) maturing females had a significantly higher hepatosomatic index than males and immature fish. An increase in dry matter and fat and a decrease of protein were observed in the muscle of maturing males and immature fish towards the spawning season, while maturing females had a slight fall in dry matter and fat and a small increase in protein in the same period. Dry matter and fat in muscle of rainbow trout were positively correlated.     

Gag (Mycteroperca microlepis) vitellogenin: purification,characterization and use for enzyme-linked immunosorbent assay (ELISA) of female maturity in three species of grouper

Circulating levels of the egg yolk precursor protein, vitellogenin (VTG), can be used as a biochemical indicator of maturation in female fish. Here we report on purification and partial characterization of VTG from a temperate marine serranid, the gag(Mycteroperca microlepis). Development of a competitive, enzyme-linked immunosorbent assay (ELISA) for gag VTG (gVTG) is also described. The gVTG was purified by DEAE-agarose anion exchange chromatography from a pooled plasma sample collected from several juvenile gag after they were injected with 17estradiol. The protein appeared as a major band of M_r183000 after SDS-PAGE ± Western blotting using either a specific rabbit antiserum to gVTG or a universal monoclonal antibody for vertebrate VTGs. Amino acid composition analysis and N-terminal peptide sequencing verified that gVTG is similar in primary structure to VTG from several other teleost species. The purified gVTG and its specific antiserum were used to develop a sensitive, competitive, antibody-capture ELISA for quantifying the protein in blood plasma from maturing females. VTG levels in maturing female gag were highly correlated with oocyte growth and circulating testosterone and 17-estradiol levels, whereas VTG was non-detectable in juveniles, immature females or males. Two size-based maturity schedules for female gag were constructed, one utilizing detection of VTG in their circulation as a marker of maturity and the other relying on histological evidence that their ovaries were in vitellogenic or later stages of maturation. The two schedules were virtually identical. The gVTG ELISA was also used to detect VTG in blood plasma from mature Nassau grouper (Epinephelus striatus) and red hind (E. guttatus). As with gag, the assay was completely reliable for discriminating between reproductively mature females versus males from these two grouper species.     

Changes in plasma somatolactin levels during spawning migration of chum salmon (Oncorhynchus keta)

Plasma somatolactin (SL) concentrations were examined in chum salmon in relation to gonadal maturation; immature salmon in the Bering Sea at various stages of maturation, and mature salmon during upstream migration caught at the ocean, bay and river. Plasma SL concentrations as well as plasma prolactin (PRL) and growth hormone (GH) levels in the immature fish caught in the Bering Sea were maintained essentially at similar levels. Plasma SL in mature salmon increased significantly from the fish in the ocean to the fish in the river in both sexes. Although all the fish had fully developed gonads, females completed ovulation while still in the bay, whereas final spermeation in males was achieved after entry into the river. Thus, no clear correlation was seen between plasma SL levels and final gonadal maturation. On the other hand, plasma PRL concentrations in both male and female fish were higher in the fish in the river than those in the ocean and bay, and plasma GH levels were higher in both sexes in the fish in the bay and river than those in the ocean. Plasma levels of triglycerides, glucose, free fatty acids and ionized sodium and calcium were also examined. Significant-negative correlations were seen between plasma SL and plasma ionized calcium in mature male salmon, and between plasma SL and plasma triglycerides in mature female salmon. Although our findings do not rule out the possibility of the involvement of SL in final maturation, the results indicate that SL seems to be involved at least in energy and/or calcium metabolism during the spawning migration.     

Change in flesh quality associated with early maturation of Atlantic halibut (Hippoglossus hippoglossus)

To determine the effect of maturation on flesh quality, 20 Atlantic halibut (Hippoglossus hippoglossus) consisting of mature and immature fish of both sexes were killed on site, exsanguinated and stored on ice. After 6 days of storage, the fish was gutted and filleted before colour, texture hardness and shear force were evaluated to determine the effect of maturation. Results show that mature males excreted black mucus from the skin during ice storage, while a greyish mucus was observed from immature fish. Mature fish had approximately 2% lower slaughter yield and 6% lower fillet yield compared with immature fish. The fillets from mature males were significantly harder compared with fillets from immature fish and the muscle structure proved to be stronger as an increased fracturability was observed in mature fish. In colour, fillets from mature fish proved to have a whiter appearance (L^*) than immature fish, while no difference was seen in a^* and b^* values. We conclude that the physiological changes associated with maturation affects the end quality, and may be related to slower growth.