Reduction of early sexual maturation in male S0 Atlantic salmon (Salmo salar L.) by dietary supplementation of tetradecylthioacetic acid (TTA)

Effects of dietary tetradecylthioacetic fatty acid (TTA) on muscle fat, development of gonads and early sexual maturation in S0 Atlantic salmon during the first year in sea were investigated. TTA (0.5% w/w) was added to the feeds for 8 weeks in the spring. In May, at the end of the TTA‐feeding period, the fish in the TTA group had significantly (P < 0.05) less fat (10.1%) stored in muscle compared with the control group (10.8%). In September, mean male gonadosomatic index (GSI) in maturing fish in the TTA group was found to be lower compared with the maturing fish in the control group (P = 0.05). On the basis of GSI values, male sexual maturation in September was 10.0% vs. 14.4% for the TTA and the control group respectively. Thus, relative to the control group, the incidence of male sexual maturation in the TTA group was reduced by about 1/3 (P = 0.002). Production data was not affected by dietary supplementation of TTA. This study reveals that TTA significantly reduces the incidence of male sexual maturation in S0 Atlantic salmon. A significant elimination model of TTA in fish muscle that takes into account, the growth rate of the fish was further developed in this study.     

Deviation of habitat salinity during seasonal gonad recrudescence affects plasma sex steroid levels and suppresses gonadal maturation in an euryhaline fish Etroplus suratensis

Impact of osmoregulation on plasma sex steroid levels and gonadal histo‐architecture was monitored to elucidate the effects of deviation from habitat salinity on gonadal recrudescence in an active reproductive season of an euryhaline fish Etroplus suratensis (pearlspot). Fish were maintained in three different salinities of 0 ppt Fresh Water (FW), 15 ppt Brackish Water (BW) and 30 ppt Sea Water (SW) for a period of 60 days. Plasma osmolality values were found to be significantly highest in SW‐acclimated fish accompanied by highest levels of plasma K? and Cl¯ ions. The progress of gonadal recrudescence was higher in BW followed by FW and SW as evident from the cellular features of gonads and increased level of plasma sex steroids, such as, in case of female and 11‐keto Testosterone and Testosterone in case of males. Plasma cortisol levels were comparatively higher in fish of both sexes in SW group. Significantly high levels of cortisol in SW suggest its role in hypo‐osmoregulation and associated stress. This study clearly reveals that salinity changes during the active reproductive phase can suppress the steroid‐mediated gonad recrudescence maximally under hypo‐osmoregulation in an euryhaline fish.     

Morphological changes during the transition from freshwater to sea water in an amphidromous goby,Sicyopterus lagocephalus (Pallas 1770) (Teleostei)

The widely distributed amphidromous goby Sicyopterus lagocephalus needs drastic change of habitat to fulfil its life cycle: adults live and spawn in rivers, where eggs hatch into prolarvae that have to reach the sea to acquire characteristics of planktonic larvae. Postlarvae return to rivers where they recruit and grow to the adult reproductive stage. Here, we describe the prolarval stages, namely from hatching to first contact with sea water, as well as the first marine larval stages. The observations were made under experimental conditions. We described 3 prolarval substages in freshwater (L1a–L1c). Prolarvae present a slight but visible ontogenetic development in freshwater, during which the yolk sac begins to reduce, the pigmentation increases on the body and in the eyes, and the lenses appear, although the eyes are not functional. Prolarvae need to reach the sea in a maximum of 96 h to pursue their development. Their transfer in sea water at a salinity of 36.5 induces important morphological modifications (i.e. yolk sac full absorption, appearance of pectoral fins, migration of the eyes in anterolateral position of the head, opening of mouth and anus), enabling the organisms to adapt to their new environment. This marine stage is divided into two substages: L2a corresponding to the organisation of the morphological structures adapted to the marine environment and L2b during which these morphological structures become functional. Whether it is in freshwater or sea water, the duration of the substages depends on the water temperature, but is similar for all individuals for a given temperature.     

Role of sex steroids in gonadal differentiation of the mussel Choromytilus chorus (Bivalvia Mytilidae) (Molina 1782)

In Chile, the species Choromytilus chorus stands out for its ecological and economic importance. This mussel has a very particular condition in the colour of the gonad, being cream‐yellow colour the male gonad and dark brown the female which is hardly desired by the consumers. In this context, the aim of this research is to determine the role that sex steroids have in gonadal differentiation of the mussel C. chorus. For this, juveniles with sizes 15–22 mm were selected, which were subjected to acute exposure in the form of bath for 60 days to four treatments: T1: dihydrotestosterone (DHT); T2: 17β‐estradiol (E2), T3: fadrozole (F) and T4: DHT‐F (DF), plus a control without chemicals. Each treatment as well as control included three replicates with 90 individuals each. The mussels undergoing treatment with E2 had a sex ratio (male:female) of 0.47 compared to 1:1 in the control group. In contrast, in the groups treated with DHT, F and DF the sex ratio changed to 2.0, 1.60 and 1.70 respectively. In the fertilization trials, all the mussels produced functional gametes, as they were able to generate gametes that were developed to morula, and veliger larva. Nevertheless, it should be noted that the size of oocytes from the group exposed to estradiol (61.12 ± 2.40 μm) was significantly higher than in other groups. These results support the hypothesis that sex steroids would be involved in sexual differentiation of marine bivalves.     

Use of reflex indicators for measuring vitality and mortality of the snow crab (Chionoecetes opilio) in captivity

The snow crab (Chionoecetes opilio) is one of the most important commercial crabs in the world; it is heavily exploited in Atlantic Canada, Alaska, the Sea of Japan and the Barents Sea. Catches in the Barents Sea north of Norway have increased dramatically in the last decade. Most of the world's catch is processed, frozen and exported overseas. However, recently there has been considerable interest in exporting live snow crab, particularly in Norway. The stress of capture and live transport can result in significant mortalities. In order to establish a live export industry for snow crab, the welfare of the animal must be monitored throughout all the steps of the live transport process. In this study the reactions of snow crabs exposed to increasing periods of air exposure were measured in terms of reflex indicators, incidence of mortality, blood lactate levels and blood protein and haemocyanin. Although this is not a specific live holding or live transport process the aim was to test the suitability of reflex indicators to reflect vitality (stress) and not just to predict mortality. This would be compared with traditional blood biochemistry techniques for measuring crustacean stress. The study demonstrated that the reflex index score (RIS) is suitable to assess the vitality of snow crab. Longer air exposure periods render higher mortality rates and less vital individuals. The authors believe using vitality reflex indicators would be a suitable way of measuring crab welfare during the live holding and transport process.     

The urogenital papillae as an indicator of sexual maturity in male African catfish,Clarias gariepinus, (Burchell, 1822)

The present study investigated a non‐invasive method based on macroscopic morphological features of male Clarias gariepinus for the assessment of sexual maturity stage. As African catfish cannot be stripped for semen as in most other fish species; they have to be killed to obtain semen from the testes. This method could be used to ensure that males used to obtain sperm are sexually mature to increase the concentration and quality of mature sperm for egg fertilization in the production of C. gariepinus. Morphological features including the length and width of the urogenital papillae (UGP), an external secondary sexual characteristic of C. gariepinus (n = 89) were measured and calculated as a percentage of total body length. The urogenital papillae length (L_UGP) and width (W_UGP) index of each fish were used and compared with the macroscopic and microscopic maturity stage of the testes. The results revealed that although positive, a significant correlation does not exist between the L_UGP or W_UGP and maturity stage of the testes. Therefore, although this procedure would be valuable as an initial non‐invasive assessment of maturity, it does not provide an accurate or reliable indication of the maturity stage of the fish.     

Gonadic conditioning and maturation of the queen conch (Dosinia ponderosa) fed three microalgae at three temperatures

Gonadic conditioning and maturation of queen clam Dosinia ponderosa fed three microalgae (Isochrysis galbana, Tetraselmis suecica and Chaetoceros calcitrans) at three temperatures (20, 25 and 30°C) were assessed. Histological analysis showed six gonadic stages, indicators of maturity. The evaluation included sex proportion, oocyte diameter and frequency of gonadic stages after 22 (middle of trial) and 44 days (end of trial). At day 22, around 60% of females conditioned at 20°C, reached stage III (advances grade of maturation) when fed T. suecica. At day 44, around 50% of females were on stage III, conditioned at 20 and 25°C and fed T. suecica and C. calcitrans. For males, the best combination was C. calcitrans at 20 and 25°C. The temperature of 30°C resulted inadequate for maturation, especially when fed the diatom Isochrysis galbana. High mortalities occurred at that temperature with the three microalgal diets, especially in females. The results permits conclude that T. suecica and C. calcitrans are good sources of feed for D. ponderosa and that the best range of temperature for gonadic development is 22–25°C. These results may be basic for a best management and culture of this clam.     

Thelohanellus testudineus n. sp. (Myxosporea: Bivalvulida) infecting the skin of allogynogenetic gibel carp Carassius auratus gibelio (Bloch) in China

A Thelohanellus species was encountered during a survey on Thelohanellus diversity of Carassius auratus gibelio (Bloch) in China. The infection is characterized by the presence of large cysts of 1.4–3.2 cm in diameter in the skin of host. Mature spores were ampullaceous in frontal view and testudinate in lateral view, measuring 19.7 ± 0.7 (18.6–20.8) μm long, 7.6 ± 0.4 (6.6–8.4) μm wide and 7.3 ± 0.5 (6.6–8.8) μm thick. The single polar capsule was elongated pyriform, with 11.1 ± 0.5 (10.0–11.9) μm long and 5.3 ± 0.3 (4.3–5.8) μm wide. Polar filaments coiled with 7–8 turns. Scanning electron microscopy revealed a smooth spore surface with flat side and convex side. The sutural line was straight or ‘S’ like, running near the middle of the valves. Histologically, the large cysts consisting of numerous small plasmodia developed in the dermis of the skin. The BLAST search indicated that the newly obtained ssrRNA gene sequences did not match any available sequences in GenBank and phylogenetic analysis placed it in the Thelohanellus clade. Based on morphology and molecular differences with reported Thelohanellus spp., this parasite was described as a new species of genus Thelohanellus.     

Pelagic larval duration of three amphidromous Sicydiinae gobies (Teleostei: Gobioidei) including widespread and endemic species

Sicydiinae species have an amphidromous life cycle during which they undergo a pelagic larval phase allowing them to disperse through the ocean and to recruit in distant island rivers. Hypotheses for the differences observed in dispersal abilities between species include the variation in pelagic larval duration (PLD). However, the implication of the PLD as a proxy for explaining the dispersal ability of a species is not clear in the Sicydiinae subfamily. In this study, otolith microstructure of three Sicydiinae species was analysed. One of these species, Sicyopus zosterophorum, has a widespread distribution in the West Pacific area, whereas the other two species, Smilosicyopus chloe and Akihito vanuatu, are endemic to New Caledonia and to Vanuatu, respectively. Deposition of the daily growth increments on the otoliths of S. zosterophorum was validated using an alizarin complexone time marking technique. We estimated the PLD for the three species by counting the number of growth increments from the core to the metamorphosis check mark, and it was shorter than the one of previous studies on Sicydiinae species. The PLD of the widespread species, S. zosterophorum (54.6 ± 5.6 days), was similar to those of the endemic species, S. chloe (53.6 ± 5.7 days) and A. vanuatu (55.4 ± 7.5 days). Here, we show that in contrast to the most diverse Sicydiinae genus, Sicyopterus, the PLD could not explain endemism, and we must take into account other elements to explain the differences observed in the distribution range.     

Gonadotropin‐releasing hormone analogue multiple injection potentially accelerated testicular maturation of male yellow catfish (Pelteobagrus fluvidraco,Richardson) in captivity

The potential for accelerating testicular development and final maturation of adult male yellow catfish (Pelteobagrus fluvidraco, Richardson) in captivity was evaluated by using gonadotropin‐releasing hormone analogue (GnRHa) multiple injection, and its possible regulatory mechanism was explored by measurements of luteinizing hormone (LH) and steroid levels. The results showed that GnRHa multiple injection increased gonad‐somatic index (GSI), the sperm count and the milt‐testis index (MTI) and promoted the larvae production by elevated rates of fertilization and hatching, and lowered the rate of deformed larvae. Meanwhile GnRHa treatment decreased the percentages of spermatogonia and spermatocytes, increased the relative sperm density (RSD) and percentages of spermatids and spermatozoa (STZ), suggesting GnRHa treatment could accelerate meiotic division and enhance the formation of spermatids andSTZ. Moreover, pituitary and serum LH, as well as serum T levels were increased after GnRHa multiple injection. Taken together, the present study demonstrated GnRHa multiple injection successfully accelerated the testicular development and maturation of male yellow catfish, which was mediated by the increase in serum LH and T levels that further mediated biological and histological changes of testis. Therefore, GnRHa multiple injection could be a valuable method to induce precocious testicular maturation of adult yellow catfish with gonadal developmental arrest in captivity.     

Biological performance of Octopus vulgaris in ‘integrated aquaculture’ models: effect of two potential fresh diets,sex and sexual maturation during the grow‐out phase

Two fresh diets were tested on the biological performance of males and females of Octopus vulgaris under industrial rearing conditions in floating cages. The presence of females could potentially release paralarvae to the natural environment (‘integrated aquaculture’). Octopuses were fed on a single diet of bogue (aquaculture by‐product), and on a mixed diet (60–40% crab‐bogue), in two trials. In Trial 1 (918 ± 125 g), growth was higher in octopuses fed on the mixed diet (1.9–2.0%d^?1) than in those fed on the bogue diet (1.8–1.9%d^?1) irrespective of sex, and mortality was 3% regardless of sex and diet. In Trial 2 (1483 ± 269 g), growth was higher in males fed on the mixed diet (1.8%d^?1) than in males fed on the bogue diet (1.4%d^?1), both higher than females (1.1–1.3%d^?1), and mortality was 22–28% regardless of sex and diet. Best biological performance in trial 1 was related to the lack of functional maturation in females, evidence by the low average gonadosomatic index (2.0–3.6%) in comparison with trial 2 (8.8–11.4%), regardless of diet. No correlations between final weight and sexual maturity indices were found, so the length of the rearing period to maximize biomass increment or to release paralarvae depends on functional maturation in females.     

Effect of aromatable androgen (17‐methyltestosterone) on induced maturation of silver European eels (Anguilla Anguilla): Oocyte performance and synchronization

The reproductive performances of silver European eel in term of gonad development and egg production, employing slow‐release implants with the androgen 17‐MT (1 mg) in combination with traditional weekly injection of carp pituitary extract (CPE) was evaluated. Wild female European eels (Anguilla anguilla) underwent a standard induction protocol with CPE and were randomly divided into three groups (N‐group, no implant; Y‐group, with implant; and control, C‐group, no treatment). The results showed that 17‐MT‐treated females (Y‐group) reproduced spontaneously about 6 weeks earlier than the N‐group females with a saving of almost 40% in CPE and time of induction. Concerning artificial induction of maturation in female silver eels, our study demonstrated that they positively respond to androgen exposure also in terms of eggs productivity. Indeed, Y‐group was more productive than N‐group: in Y‐group, 11 eels ensured an eggs production that exceeded 50% of initial body weight (BW), whereas in N‐group only three eels have exceeded this value. The results suggest that 17‐MT should be considered in future protocols for the improvement of the artificial reproduction of female silver European eels.     

Spermatological research of experimentally farmed Patagonian blenny (Eleginops maclovinus) (Perciformes: Eleginopsidae) in Chile

Spermatological research of the Patagonian blennie was carried, specifically biometric parameters, sperm density, sperm count and motility in different activation mediums (815, 716, 590 and 0 mOSm kg^?1), at different temperatures (5, 10 and 15°C) and pH levels (5, 7 and 9). The results indicate that Patagonian blennie spermatozoa have a primitive form, with a total length of 44.09 ± 3.36 μm, with a head length of 2.15 ± 0.28 μm and head width of 2.5 ± 0.31 μm. The mid‐piece had a length of 0.72 ± 0.12 μm, and its tail measures 41.21 ± 3.21 μm long. The motility pattern indicates that the spermatozoa are found immobile in the seminal plasma and only initiates its movement in a hypertonic medium from 590 to 815 mOsm kg^?1. The longest motility time that was registered at 10°C in 716 mOSm kg^?1 was of 245 ± 39 s and an optimum pH of 7 was observed.     

Reproductive cycle of the rock oyster,Striostrea prismatica (Gray, 1825) from two locations on the southern coast of Ecuador

The reproductive cycle of the rock oyster Striostrea prismatica was determined at two fishing areas, General Villamil and Ayangue (located on the southern coast of Ecuador), between May 2012 and April 2013. Monthly sampling campaigns were performed at both locations. The tissues were histologically examined to determine gonadal index (GI), oocyte development, follicular area coverage and sex ratio. Surface seawater temperature, salinity and chlorophyll a concentration were measured during samplings. Our results show a similar annual reproductive pattern at both locations. The GI reached maximum values during the summer. Oysters reached highest ripeness in January and February, while spawning occurred in February–March. Gametogenesis was linked to a consistently increasing follicular area (from 1.3 ± 0.7% to 85.8 ± 7.8%) and associated to surface seawater temperature. Spawning coincided with warm water temperature fluctuations and a seawater salinity decrease. No correlation was found with Chlorophyll a concentration. The sex ratio of sampled populations was 1:1, suggesting that oysters sizing more than 10 cm in shell length present a stable sex proportion in the population. The diameter of mature oocytes was significantly reduced (32.7%) during histologically preparations in comparison to fresh oocytes. Our study provides useful information of environmental factors that may control the observed gametogenesis and spawning activity of S. prismatica.     

Effect of temperature and salinity on sex inversion in Asian Seabass (Lates calcarifer): relationship with plasma sex steroids concentration and aromatase activity of gonad and brain

Asian Seabass which shows precocious sex inversion in cultured environment is a major impediment to maintain a proper broodstocks. Seabass grown commercially in freshwater were transported to the research facility and held in freshwater at 29°C for 4 weeks and acclimatized to the experimental conditions. Fish were daily fed with a commercial pellet (50% protein, 18 MJ kg^?1) to satiety. Blood, brain and gonad collected before and at the end of the experiment were analysed for sex steroids level and aromatase activity. There was an increase in Plasma E₂ levels with temperature in fish at 34°C whereas no significant difference was observed at 24 and 29°C although the highest plasma T level was detected in fish at 34°C which had significantly lower level than at the beginning, except those held at 24°C in freshwater. Plasma 11‐KT was significantly greater in fish at 24°C compared with 29 or 34°C which had clear opposite to the E₂. Aromatase activity in brain was higher at 29°C than at either 24 or 34°C, whereas gonadal aromatase recorded highest at 34°C. These findings concluded that high temperature in culture facility induces sex inversion of Asian Seabass.     

Effects of androgenic gland ablation on growth,sexual characters and spermatogenesis of the white shrimp,Litopenaeus vannamei (Decapoda: Penaeidae) males

This research was implemented to study the effects of androgenic gland ablation in the white shrimp Litopenaeus vannamei to explore sex reversal potential as an alternative technology for monosex female mariculture based on the sex dimorphic growth of this species. The surgical procedure was applied to male postlarvae (PL) at different ages, after external sex differentiation, as well as in sex undifferentiated PL. Andrectomized males regenerated normal appendices including pereiopods and pleopods; however, body growth and relative size of regenerated petasmas and appendices masculinae were statistically inferior (P ? 0.05) to control males. Spermatogenesis in andrectomized males was active, but a phenomenon of degradation of spermatids and reproductive tissues was detected. No sex reversal was accomplished regardless of PL age from sex undifferentiated stages (PL38) to sex differentiated stages (?PL55). The complete regeneration of sexual characters in andrectomized L. vannamei (Dendrobranchiata) is different from previous reports from Decapoda.     

室内养殖条件下中华绒螯蟹雄性个体的生殖潜力

为评判中华绒螯蟹育苗工作亲本投放性比(♀∶♂=2~3∶1)的合理性,通过室内连续交配实验,对雄性个体的生殖潜力进行了研究。结果显示,雄蟹具备完成3次连续交配活动的生殖潜力;个体丧失交配能力前,贡献了超过60%的精子(≥6×109个)等雄性产物;多次交配活动并没有对雌蟹的个体繁殖力产生影响;雌蟹抱卵后,纳精囊亦没有出现明显的偏差;实验条件和基地育苗池个体纳精囊内均还存有一定数量的精子,表明雄蟹提供的雄性产物可以满足雌蟹受精的需要,因此,该性比在实际育苗生产中具有一定合理性,而作为亲本雄蟹的大规格及自身的生殖策略则可能是中华绒螯蟹避免精子限制发生的重要原因,其潜在的精卵比达(1.59~10.86)×10~3∶1。此外,研究成果揭示这个被广泛采用的亲本性比存在进一步优化的可能,可以提升至4∶1。     

The effects of a prolonged photoperiod and light source on growth,sexual maturation,fin condition,and vulnerability to fungal disease in brook trout Salvelinus fontinalis

The effects of an artificially prolonged photoperiod on growth, survival rate, colouration, and sexual maturation in brook trout Salvelinus fontinalis during pre‐ and post‐spawning periods from 21 June to 06 November were investigated. Fish of mean initial weight ?150 g were reared at ambient photoperiod as well as with an artificially prolonged photoperiod produced by either a light‐emitting diode or a metal‐halide light. The fish groups subjected to a prolonged period of artificial light grew significantly larger and had a higher survival rate (p < 0.05), regardless of sex, and showed lower occurrence of fungal disease compared to controls reared in the natural photoperiod. We found a significantly higher number of sexually mature fish in the control groups compared with experimental groups. The increased photoperiod effectively delayed gonad development and increased somatic growth in both male and female brook trout, and also increased resistance to fungal disease. The increased photoperiod produced an observable difference in fish colouration, with control groups exhibiting more intensive spawning colouration.     

Retracted: Study of testis histology and sperm morphology in the Bunnei,Barbus sharpeyi (Gunther, 1874) induced by luteinizing hormone‐releasing hormone analogue and carp pituitary extract

This study was conducted to determine the effects of hormone treatment on testis structure in Barbus sharpeyi, as well as the morphology of sperm examined by scanning electronic microscopy (SEM). Male B. sharpeyi were divided into three groups (three fish per group) and injected with luteinizing hormone – releasing hormone analogue (LHRH–A₂) or carp pituitary extract (CPE). The first and second groups were treated with 10 μg kg^?1 LHRH–A₂ and metoclopramide (MET), and their testis were sampled pre‐ and Poststripping respectively. The third group received 2 mg kg^?1 CPE and were killed pre‐stripping. Based on the histological results obtained, the testicular connective tissue of the lumen was thicker, and seminal vesicles were of a lower volume, in fish injected with CPE in comparison to the other groups. After treatment with LHRH–A₂ and MET, not all spermatozoa within the testis were ejaculated, and only a small amount of sperm was obtained by abdominal stripping. The highest and lowest diameters of connective tissue within lobules were observed in fish receiving CPE and LHRH–A₂ treatments respectively. There was a significant difference (P < 0.05) in lobule space between the fish injected with the CPE and the fish injected with the LHRH–A₂ and MET. The SEM results revealed that the spermatozoa of B. sharpeyi were composed of a spherical to elliptical head, a cylindrical midpiece, and a lengthy flagellum. In conclusion, it was found that injection with LHRH–A₂ and MET improved the spermatogenic process in comparison to injection with CPE.     

Pre‐impoundment stock assessment of two Pimelodidae species caught by small‐scale fisheries in the Madeira River (Amazon Basin – Brazil)

The middle stretch of the Madeira River has supported an intensive commercial fishery for several decades. Developed in an area of rapids and waterfalls, this fishery focuses primarily on catfish stocks, mainly pimelodids. Data from fish landings collected in the years immediately prior to the start in operations of two large hydroelectric dams were used to estimate growth and mortality rates for Pirinampus pirinampu (Spix & Agassiz) and Brachyplatystoma platynemum Boulenger. In addition, stock assessment was carried out for both species, and the results used to evaluate the status of the fishery. Mean population parameters were L_∞ = 80.85 cm (total length), k = 0.52 year^?1, ? = 3.53, A_0.95 = 6 year, M = 0.87, F = 1.41–1.64 and Z = 2.28–2.51 for P. pirinampu; and L_∞ = 95.55 cm (total length), k = 0.28 year^?1, ? = 3.40, winter point = 0.41, A_0.95 = 11 year, M = 0.55, F = 0.16–0.35 and Z = 0.71–0.90 for B. platynemum. Yield‐per‐recruit analysis indicated P. pirinampu was overfished and that the stock of B. platynemum was under‐exploited. Moreover, overfishing of the P. pirinampu stock and the effects of fragmentation caused by the construction of the dam should be monitored.