Efficacy, tissue distribution, and residue depletion of oxytetracycline in WS-RLP infected California red abalone Haliotis rufescens

Oxytetracycline (OTC) was recently demonstrated to be an effective therapeutant for California red abalone (Haliotis rufescens) infected with the agent of withering syndrome (WS), a Rickettsia-like prokaryote (WS-RLP). This study examined the influence of temperature on the efficacy and pharmacokinetics of oral OTC treatments on WS-RLP infected red abalone, H. rufescens. Medication was administered in an artificial diet containing 1.85% active OTC at a rate of 103.4 mg/kg abalone for 10, 20 and 30 days at both 13.4 °C and 17.3 °C. Drug residue concentrations, WS-RLP burden and WS-associated pathological changes within foot muscle and digestive gland were measured 3, 17, 23, 42, 63, 81, 102, 122, and 160 days after OTC treatment. In all samples the highest concentrations of OTC were detected on the first sample day. Furthermore, all sampling periods showed significantly less OTC in foot muscle samples relative to corresponding digestive gland samples (p < 0.001). While drug depuration occurred rapidly from foot muscle, unusually high concentrations and long depuration times were measured within the digestive gland. The pharmacokinetic trends in both the foot muscle and digestive gland at 13.4 °C were adequately described by a one-compartment model, while the digestive gland depuration models within the 17.3 °C treatments conformed to a two-compartment model. At both temperatures treatment duration gave rise to significant differences in OTC accumulation and depletion (p < 0.001). Despite this, terminal elimination rate constants were similar. Estimated half-lives were similar among all treatments for digestive gland (23.8–27.5 d) and all treatments for the foot muscle at 13.4 °C (10.7–13.4 d; calculated only for the 13.4 °C treatments). At both temperatures all three durations of drug treatment led to significant reductions in WS-RLP prevalence, foot muscle atrophy, and mortality. WS-RLP re-challenge trials initiated 44, 88, and 122 days following the 10-day treatment at 17.3 °C showed reduced susceptibility to re-infection for up to 88 days after treatment, suggesting that digestive gland OTC residues confer long-term resistance to pathogen. Atomic absorption spectroscopy conducted on both foot muscle and digestive gland found significantly higher concentrations of iron, zinc, and manganese in the digestive gland, offering an explanation behind the underlying mechanism of OTC retention for extended periods within this tissue.     

Induced triploidy and tetraploidy in the European flat oyster, Ostrea edulis L.

Eggs of the European flat oyster, Ostrea edulis, were treated with cytochalasin B (1 mg/l, 20°C, 20 min), at different time intervals after in vitro fertilization. Ploidy levels were assessed by chromosome counting on 1- and 54-day-old specimens. Evidence for bimodal distribution was found to separate meiotic I and meiotic II triploids. Peaks were located at 30–35 min and 90–100 min post-fertilization, triploid rates reaching 70% and 68% respectively. Tetraploid embryos were induced in two major groups. The effective shocks were those applied at 5–25 min and 260–280 min after fertilization (respectively 40% and 53% tetraploid metaphases). Karyological examinations of embryos and spat, carried out 20 h and 54 days after fertilization, showed a differential mortality among triploids and diploids in all treated groups and no tetraploids among the spat.     

Filtration of king scallops (Pecten maximus)

Filtration rates of hatchery-reared king scallop (Pecten maximus L.) juveniles, fed a single species alga diet (Pavlova lutheri (Droop) Green), were measured at a range of temperatures (6–21 °C). Weight specific filtration rate (ml min⁻¹ g⁻¹ (live weight)) of juveniles of a selected size range of 17–19 mm shell height (0.26–0.36 g live weight) increased with temperature above 16 °C and decreased below 11 °C, but was not significantly different between these two temperatures. Measurements at 16 °C using juveniles with a wider size range of 10–25 mm shell height (0.05–0.8 g live weight) gave the allometric equation: filtration rate (ml min⁻¹)=12.19×weight (g)^0.887. Filtration rate decreased significantly when the cell concentration was greater than 200 cells μl⁻¹ (4.25 mg (organic weight) l⁻¹). With six other algae food species, filtration rates similar to those with P. lutheri were only achieved with Chaetoceros calcitrans (Paulsen) Takano. All other algae species tested were cleared from suspension at significantly lower rates. Experiments with diet mixtures of P. lutheri and these other algae suggested that this was usually a reflection of lowered filtration activity, rather than pre-ingestive rejection of cells. In experimental outdoor nursery rearing systems, the filtration rate was inversely proportional to the concentration of cells in the inflow, in the range 5–210 cells μl⁻¹. It was not affected by flow rate (2–130 l h⁻¹, equivalent to 0.12–28.38 l h⁻¹ g⁻¹ (live weight)) with scallop juveniles stocked from 2 to 62 g l⁻¹. The results are discussed in relation to on-growing scallops at field sites.     

Measurements of oxygen consumption and ammonia excretion of Atlantic salmon (Salmo salar L.) in commercial-scale, single-pass freshwater and seawater landbased culture systems

The oxygen consumption of Atlantic salmon was measured in large culture tanks for a period of 20 months from the parr to the adult stage. In addition, diurnal sampling was conducted for estimation of both oxygen consumption and ammonia excretion. The oxygen consumption was affected especially by temperature, season and smoltification. For parr the oxygen consumption rate was 1–6 mg O₂/kg min and the ammonia excretion rate was 0·037–0·13 mg N/kg min from autumn to spring. The corresponding rates for adult salmon during the period October to July were 1·5–4·5 mg O₂/kg min and 0·075–0·13 mg N/kg min.     

Effect of water temperature on the immune response of white shrimp Litopenaeus vannamei to Vibrio alginolyticus

White shrimp Litopenaeus vannamei held in 25‰ seawater at 27 °C or 28 °C were injected with TSB-grown Vibrio alginolyticus at 1 × 10⁴ colony-forming units (cfu) shrimp^− 1 or 1 × 10⁵ cfu shrimp^− 1, and then cultivated onward at water temperatures varying from 20 to 34 °C. Over 24–144 h, mortality of V. alginolyticus-injected shrimp held at 34 °C or 32 °C was significantly higher than that of shrimp held at lower temperatures. In a separate experiment, shrimp held in 25‰ seawater at 28 °C and then cultured onward at 20 to 32 °C were examined for immune parameters at 24–96 h. THC, phenoloxidase activity, respiratory burst, and SOD activity decreased significantly at 24 h after transfer to 32 °C. Shrimp held in 25‰ seawater at 27 °C and then cultured onward at 20 to 34 °C showed a significant reduction in phagocytic activity and clearance efficiency for V. alginolyticus at 24 h after transfer to 34 °C. It was concluded that transfer of shrimp from 27 or 28 °C to higher temperatures (32 and 34 °C) reduced their immune capability and decreased resistance to V. alginolyticus infection.     

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.     

Hormone-induced spawning of the Australian freshwater fish Murray cod, Maccullochella peeli (Mitchell) (Percichthyidae)

Murray cod, Maccullochella peeli, originally captured from the wild, underwent normal gonadal development in earthen ponds. Handling of broodfish in the 3 months before a breeding season caused atresia and resorption of oocytes in most females. Cod were removed from the ponds when the water temperature reached 20°C during spring, and final oocyte maturation and ovulation were induced in mature females by injecting 1000 or 2000 IU/kg human chorionic gonadotrophin (HCG) or 2–5 mg/kg of a preparation of the pituitary gland from common carp (CPG). Control treatments and dosages of 100–750 IU/kg HCG did not induce ovulation. Broodfish were held at 21 ± 1°C in 2000-l tanks after injection. The time of stripping and fertilization of Murray cod eggs was an important factor determining their hatchability. There was generally high post-fertilization mortality of eggs stripped within 1 h or between 4 and 6 h of ovulation, but high hatchability of eggs stripped 2–3 h after ovulation. The mean hatchability of eggs stripped 48.5–49.5 h after the injection of 1000 IU/kg HCG was 79.8%, but there were significantly lower mean hatchabilities of eggs stripped after 46–48 h and 50–52 h, as well as after the injection of 2000 IU/kg HCG. Results using CPG were variable. Possible reasons for the high post-fertilization mortality of Murray cod eggs are discussed, and techniques for broodfish handling, injection, stripping and the fertilization and incubation of eggs are presented.     

Effects of storage temperature and duration on the setting and post-set spat survival of the tropical oyster, Crassostrea iredalei (Faustino)

The effects of six storage temperatures (5°C, 10°C, 15°C, 20°C, 25°C and room temperature) and six storage durations (6, 12, 24, 48, 72 and 96 h) on pre-settlement larvae of Crassostrea iredalei indicated that settlement rate deteriorated with time for all temperatures. The highest settlement rate (40.1%) was attained at a storage temperature of 20°C for 6 h. This was followed by 10°C and 15°C for 6 h, with mean percent sets of 35.4% and 33.5%, respectively. An above-average set of 29.5% was obtained for the control larvae (larvae directly from the rearing tanks) compared to larvae stored between 10°C and 20°C for 12 to 24 h (21.1–28.2%). Average sets obtained for storage between 10°C and 20°C was 16.6–19.7% for up to 48 h, and sets for room temperature (ca. 30°C) and 5°C for 12 h were 11.9% and 16.9%, respectively; whereas at 25°C the set rate was 10.7% for 6 h. Storage at all other levels of temperature and duration resulted in poor set rates of less than 8%. All successfully set larvae from this experiment were further kept in the hatchery for three weeks to observe their short-term post-settlement survival. Survival rates were closely related to the setting rates, whereby higher sets contributed to better survival rates. The highest survival rates, 61.3–84.8%, were recorded for larvae set at temperatures ranging from 10°C to 20°C with a storage time of up to 48 h. These levels were comparable to the control (68.0%) and 5°C for up to 12 h (68.9%). Storage at 72 h resulted in total mortality at all temperatures, except for those stored at of 10°C (51.5% survival) and 20°C (14.7%).     

Welfare aspects of live chilling and freezing of farmed eel (Anguilla anguilla L.): neurological and behavioural assessment

The overall objective of the study was to evaluate a slaughter method of eels, which consisted of chilling until their body temperature was <5 °C for stunning, and subsequently placing them in cold brine at −18 °C for 15 min for killing. Three distinct experiments and a control were performed.

Firstly, 19 eels with an average live weight of 758±44 g were restrained and equipped with EEG, ECG electrodes and a temperature sensor inside the body. Then, they were placed in the ice water. Indices for the induction of unconsciousness and insensibility were the appearance of theta and delta waves and no response on pain stimuli, which disappeared at a body temperature of 8.0±2.1 °C after 12±5 min in 15 eels. The responses to pain stimuli did not disappear in three eels. Within a confidence level of 95%, the percentage of eels that is not effectively stunned during the procedure in ice water of <5 °C was at least 5%. The heart rate decreased from 24±10 beats/min (n=14) to 7±4 (n=11) and became irregular during cooling down. When placed in the brine water of −18 °C, the EEG showed rapid and extreme depolarisation of the membranes, which started after 27±17 s (n=18). The ECG showed fluttering of the heart in all eels. None of the eels recovered after this procedure.

For 10 eels with an average live weight of 128±27 g, it was observed that the body temperature decreased from 17.1±0.6 to 4.0±0.5 °C in the ice water. After 15 min in the brine water of −16.1±2.2 °C, the body temperature decreased to −3.1±2.3 °C.

Finally, three groups of seven eels and eight single eels were placed in ice water of −0.0±0.1 °C. The observation of unrestrained eels revealed four phases. Animals were (1) swimming around in the water, (2) attempting to escape from the ice water, (3) pressing their nose to the wall or corner while showing clonic muscle cramps, and finally (4) breathing only, while all other muscle activity was totally suppressed. Afterwards, they were transferred to cold brine at −18 °C, and none of the eels recovered.

The eight control eels, which were transferred to water at 18 °C, swam around, except for one that was lying in an S-shape position at the bottom. After 570 and 605 s, two eels tried to escape from the box.

The obtained results show that the eels, which were transferred from water at 18 °C to ice water, might be stressed, a specific behaviour and an irregular heart rate were observed. From an animal welfare point of view, it is therefore not recommended to stun eels by live chilling. Moreover, at least 5% of the eels will not be stunned at a body temperature of <5 °C. Placing eels in brine water of −18 °C is an effective method to kill the eels before slaughter. However, it cannot be recommended to place conscious eels in cold brine water, because it takes more than 27 s before unconsciousness may be induced.     

Responses to predators of cultured and wild red abalone, Haliotis rufescens, in laboratory experiments

Hatchery-spawned and reared abalone that are placed onto subtidal reefs to enhance native populations often suffer a high mortality. A potential source of mortality is behavioral differences of cultured and wild abalone. Controlled observations and factorial experiments in the laboratory were used to examine abalone behavior and mortality rate due to three predators — crabs, sea stars and lobsters — on small reefs in laboratory tanks. Two abalone types — cultured and wild — and two age/size classes, 0+ (8–20 mm shell length) and 1+ (25–50 mm), were used. Abalone types differed in their movement patterns, with wild animals moving rapidlyto concealed positions within the reefs and most cultured abalones remaining in their original positions for several hours. Over all experiments, there were differences in predation rates by crabs, lobsters and sea stars, with crabs consuming the most abalone and sea stars the least. Significantly more cultured than wild abalone were consumed in an experiment in which different combinations of predators were present. No consistent differences were seen in the consumption of the two size classes of abalone. Animals fresh from the hatchery suffered significantly higher mortality and were more sluggish in their responses to predators than hatchery-reared abalone that had been acclimated to laboratory conditions. The results suggest, however, that cultured abalone may acclimate relatively quickly to a new environment, which may be useful for future attempts at transplanting these animals.     

Induction of triploidy in the turbot (Scophthalmus maximus): II. Effects of cold shock timing and induction of triploidy in a large volume of eggs

Triploidy was induced in the turbot (Scophthalmus maximus, L.) by applying cold shocks shortly after fertilization. The combined effects of the timing of cold shock commencement after fertilization, cold shock duration and cold shock temperature were investigated. Ploidy was assessed by counting the number of nucleoli per nucleus (NOR) in larvae and also by measuring erythrocyte size in juveniles. A clear peak in triploidy induction was obtained when shocks were started between 6 and 7 min after fertilization at a pre-shock temperature of 13–14°C. With this timing, shocks of 20-min duration at 0°C gave >90% triploidy, with survival about 80% of the untreated controls. In order to ensure both high triploidy rates and high survival, it was necessary to carefully maintain the water temperature just below 0°C. Experiments with small and large volumes of eggs were performed in order to determine how changes in the relative volumes of eggs and chilled water could affect survival and triploidy induction. The best combination to induce triploidy in the turbot was as follows: shock commencement 6.5 min after fertilization, shock duration 25 min, and shock temperature between 0 and −1°C. With this combination, 100% triploidy could consistently be induced with survival 60% of the untreated control. This was successfully applied to a large volume of eggs (300 ml; 1 ml 800 eggs) in order to mass-produce triploid turbot. Triploids had lower survival rate than diploids at hatching but similar thereafter, with the ability to complete the different stages of larval rearing, indicating the viability to produce triploid turbot under farming conditions.     

Effect of temperature on hatching success and size of striped trumpeter (Latris lineata) larvae

Egg samples were collected from captive striped trumpeter maintained under phase-shifted and simulated ambient photothermal regimes and incubated at 9, 10, 11, 12, 13, 14, 15 or 16 °C. No eggs hatched at 9 °C. Time to hatch decreased from 9.6 to 4.2 days as temperature increased from 10 to 16 °C. Survival to hatch was low at 10 and 11 °C, but similar within the range 12–16 °C. Larval length at hatching was greatest at 14 °C, with no significant difference in yolk volume or muscle depth at vent across the range of temperatures. The results of our study suggest that the optimal temperature for the incubation of striped trumpeter eggs is 14 °C, which is higher than found previously.     

The quantitative dietary protein requirements of Penaeus monodon juveniles in a controlled environment

Penaeus monodon juveniles (average WEIGHT = 1.32 g) were kept in individual 2 l perforated plastic containers, 10 of which were placed in each of the twenty-four 50 l rectangular wooden-glass aquaria supplied with seawater filtered through a sand-gravel filter (32–34 ppt; 26.5–29.0°C; pH, 7.6–8.2) at 0.8–1.01 l/min. Eight diets were prepared containing 25–60% protein and fed at 10% of the body weight/day for the first 2 weeks and 8% for the succeeding 4 weeks.

Shrimps fed the 40% protein diet produced the best growth, feed conversion ratio (FCR), protein efficiency ratio (PER) and survival rate. However, shrimps fed the 30, 35 and 45% protein diets produced comparable results. The protein content of the shrimps was directly related to the level of protein diet up to 50%; whereas fat content seemed to be inversely related up to 50% protein diet.     

The effects of temperature and diet on the survival, growth and food uptake of aquarium-held postpueruli of the rock lobster Jasus lalandii

Aquaculture of the rock lobster Jasus lalandii has been considered, but is hindered by a paucity of knowledge about conditions that promote yields. This study investigated the influences of temperature and diet on the growth of aquarium-held postpueruli of J. lalandii. First, postpueruli (11.5±0.2 mm CL) were exposed to temperatures spanning 12–24 °C for a total time period of 77 days, while being given a constant diet of mussel flesh. Under these conditions, intermoult period (IMP) was longest at 12 °C (50.6±1.2 days) and at 24 °C (>57 days), and shortest at 18 °C (35.5±1.1 days). Growth increments (GI) were large at 12–18 °C, smaller at 21 °C and negative at 24 °C. Survival was 100% at 12–16 °C, above which mortalities rose to 70% at 24 °C. Food consumption, body mass and condition all peaked at 18 °C. Thus, growth was optimal at 18 °C, but survival greatest at 12–16 °C.

Second, diet-controlled experiments examined the effects of three different diets (blue mussel, commercial shrimpfeed or an alternation of the two) on survival, growth (IMP and GI) and food uptake of postpueruli (11.0±0.3 mm CL) held at 18 °C for a total time period of 77 days. Feeding rate, average growth, body mass and condition were all highest on the mussel diet, and lowest on the shrimpfeed, and the postpueruli consumed more mussel flesh than shrimpfeed. There was little difference in survival of postpueruli subjected to the three diet treatments.

A diet of exclusively blue mussel yielded higher growth, body mass, condition and food uptake than a diet of either shrimpfeed alone or an alternation of mussel and shrimpfeed. The postpueruli acclimated well to culture conditions and survived on a diet of artificial pellets, thus showing good potential for mariculture. On the present evidence, greatest returns are likely at 16–18 °C and with a diet of mussel flesh.     

Sublethal effects and safe levels of carbon dioxide in seawater for Atlantic salmon postsmolts (Salmo salar L.): ion regulation and growth

Atlantic salmon (Salmo salar L.) postsmolts (0.17–0.26 kg) were exposed to four different levels of carbon dioxide partial pressure for 43 days in an open flow system: 0.6 mm Hg (control), 4.9 mm Hg (low), 12 mm Hg (medium), and 20 mm Hg (high). The water temperature was 15–16°C and the salinity 34‰. In the low carbon dioxide group (P_CO2=4.9 mm Hg; 10.6 mg/l), no significant differences were found in blood parameters (haematocrit, plasma chloride and plasma sodium) or in growth parameters (weight, length and condition factor) when compared to the control group. After 43 days, the mean plasma chloride concentration for the medium group (P_CO2=12 mm Hg; 26 mg/l) was significantly reduced, while weight and condition factor were slightly, although not significantly, lowered. For the high carbon dioxide group (P_CO2=20 mm Hg; 44 mg/l) plasma sodium and plasma pH were significantly increased and plasma chloride, oxygen consumption, weight, length and condition factor were significantly reduced at the end of exposure. There was no mortality in the control group or in the low carbon dioxide group. The mortalities in the medium and high carbon dioxide groups were 1.1 and 4.3%, respectively. Nephrocalsinosis was not observed in any of the groups. The results of the present investigation indicate that the CO₂ concentration of the low group may represent a safe level for Atlantic salmon postsmolts when the temperature is 15–16°C and the oxygen level is 6–7 mg/l. Further studies are required.     

Artificial incubation of Japanese crayfish (Cambaroides japonicus) eggs by using a simple, easy method with a microplate

We developed a simple, easy method with a microplate to artificially incubate Japanese crayfish (Cambaroides japonicus) eggs for their cultivation. We prepared 6-, 12-, 24-, 48-, and 96-well microplates containing sterile water heated to 5, 10, 15, and 20 °C. Fourteen experimental groups for each water temperature were prepared for each of different water volumes (0.125–10 ml) in each well. One embryonic egg was placed in each well. Experiments were also conducted with water collected from the lake where the eggs were harvested from and held at 15 °C. In the microplates with sterile water, high proportions of eggs hatched (60–100%) at 15 °C in all volumes of water, although the proportions of hatching were low (0–20%) at 5, 10, and 20 °C. All eggs died in the experiments that used lake water. We conclude that the 96-well would be the most effective size to hatch crayfish eggs in, because of its convenience. This method using a microplate is simpler and easier compared with methods of previous studies to artificially incubate crayfish eggs, and therefore it might be useful to incubate eggs of other freshwater crayfish species.     

Pharmacokinetics and tissue distribution of oxytetracycline in sea bass, Dicentrarchus labrax, at two water temperatures

A pharmacokinetic study of oxytetracycline (OTC) following an intravascular administration (40 mg/kg) was carried out in sea bass, Dicentrarchus labrax (110 g), at 13.5 and 22 °C water temperature. Blood, muscle and liver samples were taken at 1, 2, 4, 8, 16, 32, 64 and 128 h post-injection. The plasma data were conformed to a two-compartment model. The kinetic profile of the drug was found to be temperature dependent. The absorption half-life (t_1/2) of OTC was 0.98 and 0.192 h at 13.5 and 22 °C, respectively, whereas the elimination half-time (t_1/2β) of the drug was 69 h at 13.5 °C and 9.65 h at 22 °C. The apparent volume of distribution of the drug at steady state [V_d(ss)] was 5.62 l/kg at 13.5 °C and 2.59 l/kg at 22 °C. The mean residence time (MRT) of OTC was found to be 37.7 h at 22 °C and 71 h at 13.5 °C. The total clearance of the drug (CL_T) was calculated to be 73.5 and 68.7 ml/kg/h at 13.5 and 22 °C, respectively.

Liver levels indicated higher OTC values than respective muscle levels at all time points and for both temperatures. The elimination of OTC from tissues tested was faster at the high temperature, whereas the drug was eliminated faster from liver compared to muscle when comparisons are made at the same temperature.     

Effect of starvation on the growth and survival of post-larval abalone (Haliotis iris)

The starvation tolerance of post-larval abalone (Haliotis iris) was determined by examining post-larval growth and survival after various periods of starvation. Competent larvae (10 days old at 16°C) were induced to attach and metamorphose with 2 μM GABA. Post-larvae were either fed diatoms (Nitzschia longissima) or starved. In Experiment 1, post-larvae were starved immediately after metamorphosis for periods of 1, 2, 4, 8, 15, 20, 25 and 30 days. Starved post-larvae grew relatively well for several days after metamorphosis despite the absence of food (averages of 10.4 and 17.8 μm shell length (SL) per day after 8 days for two batches). Subsequent growth was minimal, averaging 1.7 and 0.7 μm day⁻¹ over 6–7 days for the two batches. There was no clear relationship between period of starvation and growth rate when fed. Mean daily growth rate over 3 weeks when fed ranged from 15–22 μm day⁻¹. However, the duration of starvation did have a significant effect on survival. Survival of post-larvae fed after 1–2 days of starvation was 90–100% after 3 weeks of feeding. Longer starvation periods gave progressively lower survival and post-larvae starved for 30 days all died within a week of being fed. In Experiment 2, post larvae were fed for 3 weeks after metamorphosis, then starved for 0, 3, 7, 14 or 21 days. Growth rates of starved post-larvae averaged only 5–6 μm day⁻¹ in the first week (vs. 30 μm day⁻¹ in controls), and later declined to zero. Growth resumed within a week following return to food, but the 14- and 21-day starvation treatments took 2 weeks to reach growth rates comparable to controls. The no-starvation controls and the 3- and 7-day starvation treatments all had >70% survival over 4 weeks after return to food. Survival in the 14- and 21-day starvation treatments was 15–20%, with almost all mortalities occurring in the first week after return to food. These data suggest that Haliotis iris post-larvae are relatively tolerant of starvation, so abalone farmers have a week or so to remedy food shortages before major post-larval mortality begins.     

Manipulation of ploidy in yellow perch (Perca flavescens) by heat shock, hydrostatic pressure shock, and spermatozoa inactivation

Heat shocks, hydrostatic pressure shocks, and ultraviolet radiation were evaluated for their efficacy as methods of manipulating ploidy in yellow perch (Perca flavescens). The most effective methods of inducing triploidy were heat shocks of 28–30°C applied at a time of initiation (TI) of 5 min postfertilization for durations of 10 or 25 min, and hydrostatic pressure shocks of 9000 or 11 000 psi applied at a TI of 5 min for a duration of 12 min. These treatments resulted in triploidy induction rates that ranged from 54–100%, and embryonic survival rates of 16–80%. Cold shocks of 0°C had no effect on the ploidy or survival of embryos. For perch, hydrostatic pressure shock offered several advantages over heat shock as a method of manipulating ploidy. The most effective methods of inducing tetraploidy were hydrostatic pressure shocks of 9000 psi applied at a TI of 192 min for durations of 16 or 24 min. Ultraviolet radiation of perch sperm with doses of 3240–6480 ergs/mm² resulted in 100% inactivation of paternal chromosomes, and perch eggs fertilized with inactivated sperm had survival rates of > 50%, thereby establishing methods for producing gynogenetic perch. Studies comparing the growth and performance of diploid vs. triploid perch are underway. Tetraploid perch are being reared to sexual maturity to evaluate their potential as brood fish.     

A comparison of new in-pond grading technology to live-car grading for food-sized channel catfish (Ictalurus punctatus)

Grading trials were performed in experimental and commercial catfish ponds to compare an in-pond horizontal floating bar grader to current live-car grading. Three replicate trials were conducted in experimental ponds at three different temperature ranges (warm, >26 °C; cool, 13–26 °C; cold, <13 °C) with catfish size groups stocked in ratios of either 75:25, 50:50, or 25:75 sub-marketable (<0.57 kg) to marketable fish (≥0.57 kg). Commercial pond trials were replicated three times at each temperature range with a fish size range typical of ponds ready to harvest. Stress experienced by fish during harvest and grading was measured by mean serum glucose and cortisol levels. Grading speed was greater (P < 0.05) with the UAPB grader (105–449 kg/min) than the traditional live-car grader (0.5–0.6 kg/min). The UAPB grader decreased (P < 0.05) the proportion of sub-marketable fish during all trials. In contrast, the live car did not reduce the proportion of sub-marketable fish with the experimental methods used in this study during commercial trials or in the 25:75 distributions during warm and cold temperature trials in experimental ponds. The UAPB grader returned an average two to four times (range of 2–52) more sub-marketable fish by weight to the pond than the traditional live car method. Glucose and cortisol levels in fish graded with the two technologies were not significantly different. The UAPB grader sorted fish more accurately, consistently, and quickly than the live car at all temperatures in both experimental and commercial trials.