Immunization of grouper, Epinephelus coioides, confers protection against a protozoan parasite, Cryptocaryon irritans

The present study aimed to determine whether protection is conferred by immunization of grouper, Epinephelus coioides, against a protozoan parasite, Cryptocaryon irritans. The immunization of E. coioides was carried out by a low level exposure of fish to live C. irritans theronts from predetermined number of tomonts and by an intraperitoneal injection of a vaccine consisting of formalin-killed C. irritans theronts.

Mucus titers detected by ELISA were significantly higher in fingerling and adult grouper subjected to the low level of exposure to C. irritans theronts at 3-week post-exposure compared to fish that had no previous exposure. In addition, significantly smaller tomonts were produced from adult grouper after three successive exposures than the tomonts produced after a single exposure to the parasite.

In the vaccine-immunization experiment, no mortality was monitored in fish that received high dose vaccine (100 μg/fish), while 40% cumulative mortality and 100% cumulative mortality were recorded in low dose group (10 μg/fish) and control group (PBS-injected), respectively. In the succeeding replicate, the vaccine-immunized group (high dose) had 37.5% cumulative mortality and 100% cumulative mortality for the control. In addition, a total of 1830 tomonts were collected at 5-day post-challenge from the control group while none from the vaccine-immunized group. Significantly fewer trophonts and tomonts were enumerated at 5-day and 7-day post-challenge, respectively, in the vaccine-immunized group than the control.

Results suggest that a protective immunity has been conferred on the immunized grouper as indicated by high antibody titers in the mucus of C. irritans-exposed fish and higher survival and fewer parasites in vaccine-immunized fish than the control groups. The conferred immunity played a major role in preventing or limiting the adhesion, invasion, and development of C. irritans theronts on the skin of the immunized grouper.     

Serotonin induces ovarian maturation in giant freshwater prawn broodstock, Macrobrachium rosenbergii de Man

This study investigated the effects of serotonin (5-hydroxytryptamine or 5HT) on ovarian development in Macrobrachium rosenbergii de Man. Adult female prawns at the ovarian stage I (spent) were injected with 5HT at 1, 5, 10, 20 and 50 μg g^− 1 body weight (BW) intramuscularly on days 0, 5 and 10, and sacrificed on day 15. The doses as related to the effect could be categorized into three levels: low (1 and 5 μg g^− 1 BW of 5HT), medium (10 and 20 μg g^− 1 BW of 5HT) and high (50 μg g^− 1 BW of 5HT). The low-dose, especially at 1 μg g^− 1 BW, caused prawns to exhibit a significant increase in ovarian index (ovarian weight/body weight × 100) (5.79 ± 0.09%) as compared to the control (1.49%). The ovaries of most of these prawns could develop to stage IV (mature) and contained synchronously mature oocytes while most of the control ovaries remained at stage I and II (proliferative), and contained only oogonia to previtellogenic (Oc1, Oc2) and early vitellogenic oocytes (Oc3). The medium- and high-dose treated prawns exhibited ovaries that could reach stages III and IV and contained various types of oocytes of different maturity. Pretreatment with 5HT receptor antagonist, cyproheptadine (CYP), at 10 μg g^− 1 BW before 5HT injection significantly suppressed the effect of 5HT. Intramuscular injection of the 5HT-primed thoracic ganglion culture medium into CYP-pretreated prawns resulted in the increase of ovarian index about 5–6 times more than in the control, and in the groups injected with 5HT-primed media from muscle strip, eyestalk and brain. The ovaries of most prawn could develop up to stage IV and contained synchronously developed vitellogenic (Oc4) and mature oocytes (Oc5). These findings suggest that 5HT indirectly induces ovarian development and oocytes maturation in M. rosenbergii, probably via a putative ovarian stimulating factor released from the thoracic ganglia.     

Long photoperiod delayed spawning and increased somatic growth in gilthead seabream (Sparus aurata)

The effects of extended photoperiods, mimicking the longest day of the year, were studied in 1- and 2-year seabream. The photoperiod regimes started in late July, 36 and 39 days after the summer solstice and continued for 11 months, well beyond the natural reproductive season of December–March. Regime 1 (long day, 15.5L:8.5D), which used natural and fluorescent light, reduced the incidence of maturity in both year classes and females did not spawn although some gonadal development was observed. Among all 1-year sampled fish of regime 1, a maximum of 5% became spermiating males (March) and 5% reached the yolk granule stage of vitellogenesis (VO3; 250–400 μm diameter) by May. Among 2-year sampled fish of regime 1, 45% became spermiating males and 25% were females, which reached the advanced vitellogenesis stage (VO4; 400–600 μm) by April. Regime 2 (skeleton photoperiod), consisting of natural light and a 1.5-h pulse of fluorescent light during the period 14–15.5 h after sunrise, postponed gonadal development and spawning for up to 3 months. In this regime, a maximum of 80% of 1-year sampled fish were spermiating males in February and a maximum of 10% were VO3 stage females in March. In the sampled 2-year fish, the maximum levels were 50% spermiating males in February and 25% VO3 stage females in March. Control fish, which were exposed to the natural photoperiod (29°34′N), spawned during their natural season. The maximum levels for 1-year sampled control fish were 95% spermiating males and no females in December, while among 2-year sampled fish, maxima of 75% males in February and 45% VO4 stage females in November. Final average weights of photoperiod treated fish (1-year=430 g—regime 1, 400 g—regime 2; 2-year=582 g—regime 1, 518 g—regime 2) were significantly greater (p<0.05) than control fish (1-year=341 g; 2-year=476 g). Daily feed consumption (g/100 g fish) dropped from an average of 1.83 to 0.93 g for 1-year fish during August–December and from 0.88 to 0.54 g for 2-year fish during the same period. This was correlated with reduced autumn and winter water temperatures (26–20°C summer to winter change) and increased fish weight in all treatments. Daily feed consumption was also affected by the onset of spawning in the control and regime 2 (skeleton photoperiod) treatments of both 1- and 2-year fish. The efficiency of feed utilization (FCR) and protein and energy retention were all affected by the photoperiod regimes and followed the same pattern of decrease as weight gain, regime 1 (long day)>regime 2 (skeleton photoperiod)>control.     

Self-feeding activity of a pleuronectiform fish, the barfin flounder

The self-feeding activity of the barfin flounder (Verasper moseri) was examined under natural photoperiod and temperature. The experiment, carried out over 12 weeks from September to December, involved tagged fish (mean body weight: 371 g) reared in three 1000-l tanks (3 or 5 fish per tank) with a self-feeder device. The sensor comprised a switch and trigger string with a bead. Self-feeding activity was recorded in all tanks from day 1. The fish fed mostly at night. Strong positive correlations were observed between the number of daily feeder activations and water temperature/photoperiod, and all fish grew during the experiment. These results demonstrate that barfin flounder can operate self-feeding systems and it is suggested that self-feeding activity is influenced by photoperiod and water temperature.     

Safety and efficacy of emamectin benzoate administered in-feed to Atlantic salmon, Salmo salar L., smolts in freshwater, as a preventative treatment against infestations of sea lice, Lepeophtheirus salmonis (Krøyer)

The safety and efficacy of emamectin benzoate, administered in-feed to Atlantic salmon smolts, Salmo salar L., held in freshwater, was evaluated as a preventative treatment against sea lice, Lepeophtheirus salmonis, following transfer of fish to seawater.

In the safety study, salmon smolts held in freshwater were fed with diets containing emamectin benzoate at nominal doses of 0 (control), 50 (recommended dose) and 250 (5× recommended dose) μg kg⁻¹ fish day⁻¹ for 7 days (days 0–6). Actual dose rates, based on measured concentrations of emamectin benzoate in feed, differences in fish weight, and feed consumed, were 0, 54, and 272 μg kg⁻¹ day⁻¹, respectively. On day 9, fish were transferred to seawater and observed for 14 days. No differences in feeding response, coordination, behaviour, gross and histological appearance were observed between control fish and those that received 54 μg kg⁻¹ day⁻¹. Among smolts that received 272 μg kg⁻¹ day⁻¹, approximately 50% exhibited darker coloration, and one fish (1%) exhibited uncoordinated swimming behaviour. No pathognomonic signs of emamectin benzoate toxicity were identified.

In the efficacy study, smolts held in freshwater were fed an unmedicated ration (control group) or emamectin benzoate at 50 μg kg⁻¹ day⁻¹ (treated group) for 7 days (days 0–6). On day 9, fish were re-distributed to eight seawater tanks, each holding 30 control and 30 treated fish. On days 28, 56, 77 and 109, respectively, control and treated fish in two tanks were challenged with L. salmonis copepodites. When lice in each group reached chalimus stage IV, fish were sampled and the numbers of lice were recorded. Fish challenged at day 109 were sampled for the second time when lice were at the adult stage. Efficacy was calculated as the reduction in the mean number of lice on treated fish relative to the mean on control fish. Treatment with emamectin benzoate resulted in an efficacy of 85.0–99.8% in fish challenged at days 28–77, from the start of treatment, and lice counts were significantly lower (P<0.001) on treated fish than on controls. When fish challenged at day 109 were sampled at day 128, efficacy was 44.3%, but survival of chalimus to adult lice on treated fish was lower, and at day 159, efficacy had increased to 73%. These results demonstrate that treatment of salmon smolts with emamectin benzoate in freshwater was well tolerated and highly effective in preventing sea lice infestation following transfer of fish to seawater.     

Growth and survival of larval and juvenile cobia Rachycentron canadum in a recirculating raceway system

Cobia Rachycentron canadum is a fast-growing, pelagic marine species that has recently attracted aquaculturists in both the research and commercial sectors. The typical method of grow-out for this species is in outdoor systems where production is limited to locations and seasons conducive for adequate growth and survival. Expanding the culture of cobia to indoor recirculating aquaculture systems (RAS) would allow for the production of fingerlings throughout the year and extend production to cooler regions. Two rearing trials were conducted to examine the growth and survival of cobia from hatching through 4 (trial 1, T1) or 35 (trial 2, T2) g in RAS. Cobia larvae were reared in circular tanks placed in a raceway to control water temperature and quality. During early juvenile grow-out, fish were transferred without grading to a second raceway on 29 dph (T1) or over a period of grading from 29–43 dph (T2). Larval growth (1–22 dph) measured as standard length was similar for both trials ranging from  3.9 to 14.7 mm. However, larval growth measured as wet weight (0.033 g, T1; 0.026 g, T2) or dry weight (5.7 mg, T1; 3.9 mg, T2) was significantly greater on 22 dph during T1 as was the ratio between myotome height and standard length. These differences may have resulted from an increase in initial densities from 8.7 larvae l^− 1 (T1) to 14.7 larvae l^− 1 (T2) which apparently caused an increase in food competition and overall aggression. During juvenile grow-out, cobia reached 4.0 g on 43 dph in T1 and 35.4 g on 71 dph in T2 matching weights achieved during grow-out in outdoor ponds. Over the course of both trials, survival was similar to that reported in outdoor ponds. Mean survival (± S.D.) during the early rearing phase (hatching through 29 or 43 dph) averaged 13.2 ± 3.2 % and 10.4 ± 3.2 % corresponding to final densities of 0.9 ± 0.2 and 1.2 ± 0.4 fish/l for T1 and T2, respectively. During the first grow-out phase (29–43 dph), survival of fish moved into the open raceway was 64.5% in T1 and 88.7 % in T2. Survival of cobia during the second grow-out phase (43–71 dph) for T2 was 92.5%. The results of this study indicate that cobia can be successfully cultured in indoor systems from hatching through at least 35 g without negatively affecting growth or survival.     

Extenders and cryoprotectants for cooling and freezing of piracanjuba (Brycon orbignyanus) semen, an endangered Brazilian teleost fish

The aim of this study was to develop a protocol for semen storage of piracanjuba (Brycon orbignyanus) by both cool storage at 4 °C and cryopreservation at − 196 °C. Semen was diluted in some fish semen extenders (Exp. 1) or in extenders combined with the antibiotic gentamycin sulfate (Exp. 2) and stored at 4 °C. Sperm motility was estimated every 24 h. Then, the effects of egg yolk (0 and 5%), cryoprotectants (dimethyl sulphoxide — DMSO, methanol, and methylglycol) and extenders (NaCl 154 mM, BTS™ Minitub and M III™ Minitub) on semen cryopreservation were evaluated (Exp. 3). Semen was added to each of eighteen cryosolutions (2 yolk concentrations × 3 cryoprotectants × 3 extenders), aspirated into 0.5-mL straws, frozen in nitrogen vapor (Taylor-Wharton, CP 300, “dry shipper”) and stored at − 196 °C. Sperm motility was evaluated after thawing at 60 °C-water bath for 8 s. The three cryosolutions that produced the highest post-thaw sperm motility were used again to freeze semen. Post-thaw semen quality was then evaluated under three tests: sperm motility, the percentage of live spermatozoa and hatching rate (Exp. 4). Piracanjuba semen diluted (1:10 total volume) in NaCl 200 mM or in Saad solution (NaCl 200 mM, Tris 30 mM) maintained motility above 35% for as long as 7 days, at 4 °C. Motility of only 7% was observed on undiluted semen after 3 days at 4 °C. There was neither beneficial nor detrimental effect of gentamycin on sperm motility at 250 μg/mL. Egg yolk addition to the cryosolution was beneficial in samples cryopreserved in NaCl 154 mM and in M III™, but detrimental for samples cryopreserved in BTS™. Methylglycol was the most effective cryoprotector compared to DMSO and methanol. Motility and percentage of live spermatozoa were similar among semen cryopreserved in NaCl–yolk, M III™–yolk and BTS™, all containing 10% methylglycol, but lower than fresh control. Hatching rates of eggs fertilized with sperm cryopreserved in NaCl–yolk or BTS™ were higher than for eggs fertilized with sperm cryopreserved in M III™–yolk, but lower than control fertilizations. The semen cryopreservation protocols developed here will be used to set up a gene bank for endangered piracanjuba populations.     

The use of luteinizing hormone releasing hormone analogue for ovulation induction in black sea bass (Centropristis striata)

Interest in commercial production of black sea bass has increased in recent years, but reliable spawning methods remain problematic. The objective of this study was to evaluate the effects of oocyte size and luteinizing hormone releasing hormone analogue (LHRHa) dosage and delivery systems on ovulatory success for in vitro fertilization. Vitellogenic females with maximum oocyte diameters of 400–625 μm were implanted with a 95% cholesterol–5% cellulose pellet containing 50 μg of LHRHa. Fish with maximum oocyte diameters < 450 μm failed to ovulate. In contrast, 90% of fish with 500 μm oocytes spawned within 36 h and 40% of this group ovulated a second time. All of the females containing oocytes > 550 μm ovulated. In a second experiment, females with uniformly vitellogenic oocytes (> 500 μm) and implanted with 50 μg LHRHa ovulated substantial numbers of eggs (45,000–192,000 eggs/kg body weight (BW), but fertility was consistently low (0–15%). In a third experiment, 19 of 39 females receiving implants containing 6.3–23.6 μg LHRHa/kg BW during the spawning season ovulated, but fecundity (17,000–339,000 eggs/kg) and fertilization (0–98%) were highly variable. When fish were grouped by developmental index, calculated as the number of oocytes with diameters > 400 μm/total number of oocytes measured, there were no statistical differences among groups with respect to the number of spawns, fecundity or fertilization success. In a fourth experiment, 11 of 13 females with a clutch of fully vitellogenic oocytes that were injected with 20 or 100 μg/kg BW LHRHa ovulated between 1 and 2 times on consecutive days. Five of seven given an implant containing 12.5 μg LHRHa ovulated one or more times. Fish implanted with shams or injected with vehicle alone did not ovulate in any of the experiments. No differences were found in the number of spawns, fecundity or fertilization success from fish receiving different doses of injected or implanted LHRHa. Incubation of pooled eggs produced 155,000 larvae (60% hatch) and 95,000 one-gram juveniles. These results demonstrate that injected or implanted LHRHa is effective for inducing ovulation in black sea bass with maximum oocyte diameters > 500 μm.     

Nutrients removed by Kappaphycus alvarezii (Rhodophyta, Solieriaceae) in integrated cultivation with fishes in re-circulating water

The potential of the red alga Kappaphycus alvarezii to remove nutrients was tested to treat effluents of Trachinotus carolinus fish cultivation, and the production of carrageenan in this condition was analyzed. Experiments were conducted in four tanks of 8000 L with approximately 1200 fishes of 30 g each integrated with three tanks of 100 L with 700 g of K. alvarezii, as initial biomass per tank. Seawater was re-circulated between tanks with seaweed and with fish. As a control, three tanks with seawater circulating in an open system were utilized. Seawater samples were collected daily for 10 days and concentrations of nitrate, nitrite, ammonium and phosphate were determined in the inflow and outflow water of the tanks. Significant differences between both collecting points were considered as nutrient removal by the seaweed. Growth rates and carrageenan yields were also analyzed in seaweed cultivated in seawater and in effluents. Growth rates of seaweed cultivated in tanks were lower than those obtained in open sea and in laboratory cultivation. Effluents had concentrations of nitrate and nitrite ca. 100 times higher than in the control. Maximum values of nutrient removal on effluents were: nitrate = 18.2%; nitrite = 50.8%; ammonium = 70.5% and phosphate = 26.8%. All plants survived throughout the experimental period, but some developed “ice–ice”, a disease associated with physiological stress. After the experimental period, some plants selected and cultivated in open sea presented higher growth rates in 40 days, indicating nutrient storage. No significant differences between carrageenan yields of K. alvarezii cultivated in seawater and in the effluents were observed. Our results show that K. alvarezii can be utilized as a biofilter for fish cultivation effluents, reducing the eutrophication process and can also be processed for carrageenan production, which provides an additional benefit to the fisheries.     

Use of endoscopy for gender and ovarian stage determinations in Russian sturgeon (Acipenser gueldenstaedtii) grown in aquaculture

The Russian sturgeon (Acipenser gueldenstaedtii) is native to the Caspian Sea, the Black Sea and the Azov Sea. It used to breed in the main incoming rivers, until dam construction in the mid 20th century blocked upriver spawning migration. Aquaculture of Russian sturgeon has only recently begun, prompted by their declining populations in natural habitats and the rise in meat and caviar prices. However, information on their gonadal development and puberty under culture conditions is incomplete.

Because sturgeons have no external sexual dimorphism and there are no external markers for sexing, internal examination of the gonads must be employed for gender identification as well as to monitor their development. The present study describes endoscopic and histological observations of the gonads of young Russian sturgeons aimed at identifying gender and monitoring ovarian developmental stage in females up to the age of 6 years, when they enter their first puberty cycle, as well as at 7 years of age, when they have completed vitellogenesis, under culture conditions. This information, as related to fish age and size, is of vital importance to commercial farming of Russian sturgeon for caviar production and reproduction.

For gonadal observations in both sexes, we used an endoscopic system consisting of a 4 mm, 14 cm long cystoscope sheath incorporated with fiber-optic light transmission, connected to a halogen cold light source and a miniature videocamera with a control unit attached to a color monitor. This system allowed us viewing of the fish's abdominal organs, and to save pictures of selected areas of the gonads on a computer as the fish's personal record. Ovarian biopsies were taken in parallel for histology at typical stages of gonadal development.

Gender could be identified with this system as early as at 3 years of age and the sex ratio under culture conditions of females, males and unidentified gender were 55, 40 and 5%, respectively.

Not only did large differences occur in the developmental stages of female of the same age group, but also ovarian development was highly asynchronous at the early vitellogenic stages. In late vitellogenesis, at the “gray egg” stage (1600–2600 μm diameter), the oocytes were quite regular in size and color, and remained so until the final stages of maturity.

Our study suggests that endoscopy is an efficient method for both gender identification at an early age, and for determination of gonadal development stage in sturgeon aquaculture. The ability to see the whole intact gonads of anesthetized fish can reveal important management and research information, with minimal damage or stress to the fish.     

Effects of Cu-exchanged montmorillonite on growth performance, microbial ecology and intestinal morphology of Nile tilapia (Oreochromis niloticus)

A total of 360 Nile tilapia at an average initial body weight of 3.9 g were randomly allocated to 4 treatments, each of which had three replicates of 30 fish/tank and used to investigate the effects of Cu²⁺-exchanged montmorillonite (Cu-MMT) on growth performance, microbial ecology of the skin, gill and intestine, and intestinal morphology. The dietary treatments were: 1) basal diet, 2) basal diet + 1.5 g/kg MMT, 3) basal diet + 30 mg/kg copper as CuSO₄ (equivalent to the copper in the Cu-MMT treatment group), or 4) basal diet + 1.5 g/kg Cu-MMT. The results showed that supplementation with Cu-MMT significantly improved growth performance as compared to control and fish fed with Cu-MMT had higher growth performance than those fed with MMT or CuSO₄. Supplementation with Cu-MMT reduced (P < 0.05) the total intestinal aerobic bacterial counts and affected the composition of intestinal microflora with a tendency of Aeromonas, Vibrio, Pseudomonas, Flavobacterium, Acinetobacter, Alcaligence, Enterobacteriaceae decreasing as compared with control. Measurements of villus and microvillus heights at different sites of the intestinal mucosa indicated that dietary addition of MMT or Cu-MMT improved intestinal mucosal morphology. However, the microbial ecology of the skin and gill was not affected by the addition of CuSO₄, MMT or Cu-MMT. Supplementation with CuSO₄ had no (P > 0.05) effect on the growth performance, microbial ecology and intestinal morphology. The results showed that Cu-MMT exhibited antibacterial activity in vivo and protected intestinal mucosa from invasion of pathogenic bacterium and toxins, resulting in a positive effect on the growth performance.     

An improved enzyme preparation for rapid mass production of protoplasts as seed stock for aquaculture of macrophytic marine green algae

Preparation of protoplasts and their subsequent applications for both basic and applied research of marine macroalgae remains largely under developed due to lack of development of reliable methods with consistent yields of viable protoplasts. An improved enzyme preparation with a single commercial enzyme, e.g. 2% Cellulase Onozuka R-10 in 1% NaCl solution, was developed to produce protoplasts rapidly from different green algal genera of Ulva, Enteromorpha and Monostroma. The simple dissolution of enzyme powder in 1% NaCl resulted in exclusion of 2% Macerozyme R-10 from the mixture consisting of 2% Cellulase Onozuka R-10 with 3% NaCl earlier reported as superior for the same algae. Optimal conditions for the isolation of maximum yields of viable protoplasts were found to be with 2% Cellulase Onozuka R-10 incubated at 20 °C for 2 h in 1% NaCl solution with 0.8 M mannitol adjusted to pH 6.0. The protoplast yield with optimized enzyme mixture was as high as 102.8 × 10⁶ cells g^− 1 f. wt for M. oxyspermum while it was in the range of 74.4–88.6 × 10⁶ cells g^− 1 f. wt thallus for seven species of Ulva, and 82.5–95.4 × 10⁶ cells g^− 1 f. wt for three species of Enteromorpha. The regeneration rate of protoplasts isolated using this method ranged from 89 to 92% with normal morphogenesis. The seeding of nylon threads with isolated protoplasts of M. oxyspermum was successful and after 3–4 weeks the entire frame with nylon threads became thick green in color with tiny germlings in laboratory culture. Thus, the method described in the present study allow for rapid mass production of viable protoplasts that could be potentially used as a source for seed material for mariculture and for other applied phycological research.     

The use of fish vaccines in the Chilean salmon industry 1999-2003

This study summarises the availability of fish vaccines in Chile in the period 1999–2003. Through a questionnaire survey, data on annual sales per product were obtained from seven pharmaceutical companies and data on the corresponding farmed salmonid population eligible for vaccination were obtained from Sernapesca. More than 20 vaccines for aquacultured fish were brought to the Chilean market during the study period. The estimated number of fish being immunized by immersion increased from 93 million to more than 200 million, whereas sales of fish vaccines for injection increased from 2,008 to 16,561 l, the latter amount corresponding to approx. 150 million doses. Estimated vaccine coverage in the susceptible species ranked from 37–84% for yersiniosis (ERM), from 51–17% for salmonid rickettsial septicaemia (SRS), and from 8–78% for infectious pancreatic necrosis (IPN). Vaccine coverage against bacterial kidney disease (BKD) remained below 5%.     

The effect of spectral composition and light intensity on melatonin, stress and retinal damage in post-smolt Atlantic salmon, Salmo salar

Metal halide lights are currently used as standard in commercial Atlantic salmon sea cages as a means of enhancing productivity through grilse inhibition. However, such systems create bright point light sources that are neither environment specific nor species specific and could potentially compromise fish welfare. Light emitting diodes (LEDs) are a new form of lighting technology currently being developed for the fish farming industry that can be tuned to environment and species sensitivities through narrow bandwidth outputs. However, prior to implementing these new high energy alternatives, any potential adverse effects must be determined in fish. The objectives of this study were thus (1) to determine the effect of increasing intensities of blue LED light (0.199–2.7 W m^− 2, at 0.1 m from the light source) on light perception and stress response, and (2) to examine potential retinal damage under these conditions in post-smolt Atlantic salmon, Salmo salar. A white LED light was also tested, as well as a very high intensity metal halide positive control. Results demonstrated firstly that salmon perceived blue LED light (basal melatonin levels maintained) irrespective of intensity. Secondly, fish exposed to high intensity blue LED light showed an increase in plasma cortisol and glucose levels within 3 h, returning to a basal state 24 h post-light onset. This typical acute stress response was not observed in fish exposed to the white LED light and lower blue light intensities which could indicate differential sensitivities to spectral content of the light. No effects on the non-specific immune system (lysozyme activity) were observed. Finally, extensive histological examination of the retina from fish exposed to these various light treatments revealed no signs of damage. This demonstrates the efficiency of the adaptive mechanisms to light developed in fish.     

Impact of starvation and handling stress on rigor development and quality of Atlantic salmon (Salmon salar L)

Farmed Atlantic salmon (Salmo salar L) were fed to satiation or starved for 35 d, and subjected to acute pre-slaughter stress or careful handling before slaughtering. Rigor development, post-mortem energy metabolism and quality variations were analysed during 72 h cold storage. The body weight averaged 2.9 and 3.5 kg of the fed and starved salmon, respectively. The starved salmon had lower condition factor (0.99 vs. 1.11) and higher slaughter yield (92.6 vs. 87.5%), but the fat content was similar (11.8–12.9%) in the fed and starved salmon. The initial glycogen level was lower in the starved salmon (21 vs. 29 μmol g^− 1), whereas initial ATP levels (6.4–6.6 μmol g^− 1) were not affected by starvation. Pre-slaughter stress accelerated rigor development, stimulated lactate formation through post-mortem glycolysis, and increased the breakdown of ATP and CP. The effect of stress on rigor development was less pronounced in starved salmon, and a significant interaction was observed between nutritional status and stress. Rigor development was closely correlated to ATP breakdown, especially in fillets. Acute stress accelerated flesh softening during ice storage. After 72 h storage, the fillets of the starved salmon exposed to careful slaughter handling had the significantly firmest texture, whereas the most intense fillet colour was observed in the starved/stressed salmon. Liquid leakage from the muscle during cold storage was lower in the starved salmon, but pre-slaughter stress had no significant impact. It is concluded that a starvation period of five weeks can improve the resistant to acute stress prior to slaughtering of Atlantic salmon that in turn hampers rigor development.     

Comparison of early life history stages of the bay scallop, Argopecten irradians: Effects of microalgal diets on growth and biochemical composition

The culture of bay scallops, Argopecten irradians, is limited by a reliable and affordable supply of spat and the ability to ensure that animals attain market size within a single growing season. The main goals of our study were thus: (1) to develop growth-optimizing algal diets for implementation in hatcheries, and (2) to identify and compare bay scallop postlarval and juvenile dietary requirements, especially of lipids and fatty acids, which if met may enhance production. Nutritional needs of postlarval bay scallops (present study) are compared with those of sea scallops, Placopecten magellanicus, offered the same diets in a previous companion study. To this end, postlarval (initial shell height, SH = 240 μm) and juvenile (initial SH = 10 mm) bay scallops were offered 6–7 microalgal diet combinations at 20 °C, for 3 weeks. A similar growth ranking among diets was observed between the two developmental stages. A combination diet of Pavlova sp. (CCMP 459) and Chaetoceros muelleri was far superior to any other diet tested, yielding growth rates of 58 and 357 μm day^− 1 which were 65% and 25% higher than the next highest performing diet of Tetraselmis striata/C. muelleri in postlarvae and juveniles, respectively. The T. striata/C. muelleri diet, which is limited in the n-3 fatty acid docosahexaenoic acid (DHA), yielded very poor growth of sea scallop postlarvae in a prior study, indicating that bay scallops may have less stringent requirements for DHA than sea scallops. The Pav 459/C. muelleri diet, which also supported the highest growth of sea scallop postlarvae, is characterized by elevated levels of the n-6 fatty acids, arachidonic (AA) in C. muelleri and 4,7,10,13,16-docosapentaenoic (DPA) in Pav 459. The two diets deficient in AA and n-6 DPA, Pavlova lutheri/Thalassiosira weissflogii and P. lutheri/Fragilaria familica, yielded the lowest growth rates in both bay scallop postlarvae and juveniles. Tissue enrichment of these two fatty acids relative to the diet, as well as overall enrichment in ∑n-6 fatty acids was observed across developmental stages and dietary treatments. A similar pattern has previously been observed in sea scallop postlarvae, suggesting a dietary requirement for n-6 fatty acids in pectinids that has often been overlooked in the past.     

Off flavor characterization and origin in French trout farming

The results of a study on off-flavor problems in four French trout (Onchorynchus mykiss) farms are presented. Methodological aspects on sensory analyses and volatile compounds quantification in fish are discussed. Detection of odorous compounds by gas chromatography–mass spectrometry shows that significant concentrations of geosmin (up to 18 μg/kg in fat) are found in trout. The sensory evaluation, the presence/absence of geosmin in the flesh and the identification of off-flavor compounds producers demonstrate the implication of Microcoleus in the appearance of earthy/musty off-flavors. The presence of this particular cyanobacterium is linked to the deterioration of water quality during the water recirculation period. Correlations between chemical and sensory detection in the flesh indicate that the taste evaluation enables the differentiation of the four categories “non-tainted”, “slightly-tainted”, “tainted” and “strongly-tainted”. However, the average concentrations of geosmin found for these different intensities are relatively limited, from 0.2 to 4.9 μg/kg. Finally, recommendations are made to allow a more effective control of off-flavor occurrences.     

Pharmacokinetics and the active metabolite of enrofloxacin in Chinese mitten-handed crab (Eriocheir sinensis)

The pharmacokinetics and active metabolite of enrofloxacin were estimated after single intramuscular administration (10.0 or 20.0 mg/kg body weight) to the Chinese mitten-handed crab (Eriocheir sinensis) in fresh water at 25.0 ± 1.0 °C. Levels of enrofloxacin and its metabolite ciprofloxacin in the main tissues (hemolymph, hepatopancreas, muscle, ovary and spermary) were simultaneously detected by HPLC. Enrofloxacin concentration–time profiles for the hemolymph in both tests were described by a two-compartment open model with first-order absorption. Distribution half-time (T_1/2), elimination half-time (T_1/2β), body clearance (CL/F), mean residence time (MRT_0–∞), area under the concentration–time curve from 0 to ∞ h (AUC_0–∞) and apparent volume of distribution (Vd/F), which derived from the pharmacokinetic model, were 0.427 h, 21.3 h, 0.133 l/h/kg, 60.0 h, 96.9 μg/ml/h and 4.08 l/kg, respectively, at a dose of 10.0 mg/kg body weight, and 0.216 h, 12.3 h, 0.189 l/h/kg, 85.8 h, 187 μg/ml/h and 3.35 l/kg, respectively, at a dose of 20.0 mg/kg body weight. Similarities were found between the hemolymph concentration–time curves of the two tests; for example, instant absorption process followed by the distribution phrase, and a second absorption peak at 6 h post-treatment. After intramuscular administration of 10.0 mg/kg body weight, absorption of enrofloxacin was observed in the main edible tissues (hepatopancreas, muscle, ovary and spermary), and the drug residue was the highest in the hepatopancreas, where the ‘drug sink’ phenomenon occurred. Comparative pharmacokinetics showed fast absorption, broad distribution and fast elimination of enrofloxacin in E. sinensis after intramuscular dosing. Regarding ciprofloxacin, the main active metabolite of enrofloxacin, though relatively low levels were detected in all the main tissues of the crab, its kinetics in the hemolymph in the two tests were not described by a one- or two-compartment open model.     

Prey extracts evoke swimming behavior in juvenile Atlantic halibut (Hippoglossus hippoglossus)

This study tested the efficacy of prey extracts to induce food search behavior in juvenile (15–25 cm total length, 0 year group) Atlantic halibut (Hippoglossus hippoglossus). In square culture tanks, halibut responded to shrimp and squid extract by tightly turning towards the source of the stimulus and by swimming in circles for 2–5 min following stimulus delivery. Cod extract, or a synthetic mixture consisting of glycine, proline, betaine, arginine, and alanine, failed to evoke this behavior.     

Comparative performance of Gamma Amino Butyric Acid (GABA) and 5-Hydroxytryptamine (5-HT) in the diet of larvae and post larvae of giant freshwater prawn, Macrobrachium rosenbergii: Effect of dose and route of administration on growth and survival

Three experiments were conducted to evaluate the effect of different dose and route of administration of 5-Hydroxytryptamine (5-HT) and Gamma Amino Butyric Acid (GABA) on growth, survival and pigmentation of giant freshwater prawn, Macrobrachium rosenbergii, larvae (experiment 1) and post larvae (experiment 2 and 3). In experiment 1 larva were stocked at 100 /L in seven different treatments with each of three replicates. The treatments were T1 (control), T2 (100 μg/ml of 5-HT bath exposure for 2 days), T3 (1 μM of GABA bath exposure for 2 days), T4 (0.5% 5-HT in feed), T5 (0.25% 5-HT in feed), T6 (0.5% GABA in feed) and T7 (0.25% GABA in feed). Highest growth, transformation rate, pigmentation and survival of larvae were recorded in T2 group in experiment 1. In experiment 2, post larvae were stocked at 70 per tank with 200 L of water for 45 days. This experiment consisted of 5 treatment groups with each of 3 replication viz. T1 (control), T2 (0.5% 5-HT in feed), T3 (0.25% 5-HT in feed), T4 (0.5% GABA in feed) and T5 (0.25% GABA in feed). At the end of this experiment growth was found to be higher in the control than the other treatment group showing inhibitory effect of 5-HT and GABA on growth of post larvae. To confirm the result, a third experiment was conducted for 30 days. Thirty numbers of post larvae having similar size were segregated from the previous experimental tanks (experiment 2) and stocked in the tanks of 100 L of water for experiment 3. All treatments were fed with control diet. There was similar growth pattern in all the treatments, which were higher (P < 0.05) than control, confirms the inhibitory effect of neurotransmitter in the diet of PL. Therefore, the overall results of the present study suggest that the bath treatment of neurotransmitter is superior to the dietary addition with regard to the growth, survival and pigmentation of M. rosenbergii larvae. 5-HT is more effective than the GABA for larvae of M. rosenbergii.