Ontogenetic variability of chill tolerance in larval Artemia salina: II. Dual cryoprotectants

Chill tolerance was determined for various larval stages of Artemia salina in solutions with and without dual cryoprotectants (glycerol and sucrose) and in saline solutions of corresponding osmolalities. Synchronous batch cultures of larvae were removed from a donor culture at post-hatch intervals (0, 3, 6, 12 and 24 h) and transferred immediately to solutions at -1 ± 0.2°C for 10-, 30- and 90-min intervals. Survival of control groups (cryoprotectant-free sea water, salinity 40 ppt) varied with age. In these groups, 0 h post-hatch larval survival decreased linearly with exposure time to 27.1%. Older stages, however, were insensitive to prolonged -1°C exposure after the initial 10-min period. The addition of combined glycerol-sucrose cryoprotectants to the chilled solutions enhanced survival patterns, with 0h post-hatch nauplii showing the greatest enhancement and 3-, 6- and 12-h nauplii the least. Maximum survival enhancement exceeded 250% of controls. A 4 M glycerol concentration provided more cryoprotection than 1, 2 or 3M. No enhancement was afforded any age groups maintained under hyper-saline conditions.     

Effects of docosahexaenoic, eicosapentaenoic, and arachidonic acids on the early growth, survival, lipid composition and pigmentation of yellowtail flounder (Limanda ferruginea): a live food enrichment experiment

The role of dietary ratios of docosahexaenoic acid (DHA, 22:6n−3), eicosapentaenoic acid (EPA, 20:5n−3) and arachidonic acid (AA, 20:4n−6) on early growth, survival, lipid composition, and pigmentation of yellowtail flounder was studied. Rotifers were enriched with lipid emulsions containing high DHA (43.3% of total fatty acids), DHA+EPA (37.4% and 14.2%, respectively), DHA+AA (36.0% and 8.9%), or a control emulsion containing only olive oil (no DHA, EPA, or AA). Larvae were fed differently enriched rotifers for 4 weeks post-hatch. At week 4, yellowtail larvae fed the high DHA diet were significantly larger (9.7±0.2 mm, P<0.05) and had higher survival (22.1±0.4%), while larvae fed the control diet were significantly smaller (7.3±0.2 mm, P<0.05) and showed lower survival (5.2±1.9%). Larval lipid class and fatty acid profiles differed significantly among treatments with larvae fed high polyunsaturated fatty acid (PUFA) diets having higher relative amounts of triacylglycerols (18–21% of total lipid) than larvae in the control diet (11%). Larval fatty acids reflected dietary levels of DHA, EPA and AA while larvae fed the control diet had reduced amounts of monounsaturated fatty acids (MUFA) and increased levels of PUFA relative to dietary levels. A strong relationship was observed between the DHA/EPA ratio in the diet and larval size (r²=0.75, P=0.005) and survival (r²=0.86, P=0.001). Following metamorphosis, the incidence of malpigmentation was higher in the DHA+AA diet (92%) than in all other treatments (50%). Results suggest that yellowtail larvae require a high level of dietary DHA for maximal growth and survival while diets containing elevated AA exert negative effects on larval pigmentation.     

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%).     

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.     

Some effects of temperature and salinity on laboratory-reared eggs and larvae of Polydactylus sexfilis (Pisces: Polynemidae)

Effects of temperature and salinity on eggs and yolksac larvae of Polydactylus sexfilis (Cuvier and Valenciennes) were examined in laboratory experiments. Data on developmental rates as influenced by temperature are presented. Larval length at 95% yolksac absorption was maximized between 23.8 and 28.6°C. Based on the development of functional eyes and jaws, larvae were judged capable of feeding before the yolk was completely absorbed. Larvae incubated at intermediate temperatures also had larger amounts of yolk remaining when eyes and jaws were judged functional. Temperature and salinity effects on hatching success, survival at the end of the yolksac stage, and morphological abnormalities were studied in a 10 × 5 (temperature × salinity) array of treatments. In 34‰ sea water, normalized larval survival at the end of the yolksac stage was greater than 50% between temperatures of 21.9 and 28.0°C. Larval survival decreased at lower temperatures and salinities. Proportions of abnormal larvae increased at temperature and salinity extremes, and normal development was maximized between 26 and 34‰. Larvae (74 h after fertilization) were more tolerant to extreme high temperatures than were newly fertilized eggs. Upper salinity tolerance limits of 42-h larvae were greater at 26.2°C than at 23.5 or 29.2°C, and lower salinity was less tolerated at the two extreme temperatures. Based on the results, recommended temperatures and salinities for rearing P. sexfilis eggs and early larvae are 24–28°C and 26–34‰.     

A successful microbound diet for the larval culture of freshwater prawn Macrobrachium rosenbergii

A high moisture (63–71%), semi-purified microbound diet containing alginate was compared to newly hatched live Artemia nauplii as an exclusive diet for the culture of larval freshwater prawn Macrobrachium rosenbergii from 5th stage (weighted mean) through metamorphosis to postlarva. Two separate trials, representing larvae from different hatches, were conducted. Larvae were stocked at 50/l into cone-shaped vessels that contained 2 l of 12‰ seawater and were part of a temperature-controlled (28 °C) recirculating culture system. Larvae were manually fed either the live Artemia diet or the microbound diet exclusively, several times daily. After 14 days (23 days post-hatch (dph)), growth of larvae fed the microbound diet was 90% of that achieved for larvae fed newly hatched nauplii of Artemia. Survival of larvae fed the microbound diet was 77.3% and 73.3%, and was not significantly different from that of Artemia-fed larvae. Composed of readily available ingredients, the diet contains 46.2% crude protein and 37.4% lipid, is easy to prepare, and has good water stability. The diet is an economically practical alternative to the fluctuating cost, nutrient uncertainty, and labor associated with the use of Artemia nauplii hatched from cysts. The characteristics of the diet suggest good potential for successful use in the larviculture of other fish and crustacean species, in either the existing or a modified state.     

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.     

Effect of stocking density and addition of proteins on larval survival in Japanese flounder, Paralichthys olivaceus

The effects of larval density, rearing media, and protein additions on fish larval survival were tested by rearing larvae in small containers. Yolk-sac larvae of Japanese flounder, Paralichthys olivaceus, were transferred 1 day after hatching to plastic dishes and cell-culture microplates by Pasture pipette at densities ranging from 0.3 to 30 individuals/ml and incubated at 16 °C without food. Dead larvae were removed and counted every 12 h. Three peaks of larval mortality were observed: the first peak appeared just after the transfer, the second corresponded to the completion of yolk absorption, and the third occurred 10–12 days after the transfer. Since about 50% of larvae survived until the third peak, it was clear that mortality at the second peak (completion of yolk absorption; equivalent to the first feeding) was not due to starvation. At the first mortality peak, better survival was unexpectedly recorded at higher larval densities (30 individuals/ml), suggesting that some material beneficial for survival is derived from the larvae. This idea was further supported by the improved survival in media previously used to rear larvae at high densities. The addition of bovine serum albumin (BSA) at 10 μg/ml effectively reduced mortality in microplates and in 30-l tanks. To reduce the larval mortality just after handling, addition of egg white at a dilution rate of 1/30,000 (vol/vol) or less is recommended as a practical alternative to BSA. Since the addition of polyethylene glycol 6000 (1 μg/ml) also effectively reduced mortality, reduction in mortality could not be attributed to a specific mechanism. The precise determination of the magnitude and timing of larval mortality was attained through the use of small containers, and a method to prevent mortality due to handling was identified in this study. These types of tests may allow the logical evaluation and establishment of better rearing procedures for seed production in aquaculture.     

Temperature effects on early development and occurrence of metamorphosis-related morphological abnormalities in hatchery-reared brown sole Pseudopleuronectes herzensteini

The objectives of the present study are to elucidate the effects of rearing temperatures on early larval development and the occurrence of metamorphosis-related morphological abnormalities in hatchery-reared brown sole Pseudopleuronectes herzensteini. Newly hatched larvae were reared through metamorphosis at different temperatures (6, 9, 12, 15, 18, 21, and 24 °C). Growth and development of larvae were accelerated concomitant with higher temperatures. Metamorphosed juveniles were classified into four morphological categories as normal, pseudoalbinism (two types), and ambicoloration, in combination with body color (pigmentation) and eye location. Incidence of normal morphology was lowest (11–24%) and that of pseudoalbinism was highest (74–83%) at 12 °C. The highest incidence of normal morphology (51–73%) was obtained at 21 °C. Although occurrence of ambicoloration was very low in all temperature regimes (0–10%), it increased slightly with increasing temperatures. Results of the present study strongly suggested that rearing temperature during the larval period affected the appearance of normal fish because of the different larval growth and development.     

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.     

5-Hydroxytryptamine enhances larval development of the giant freshwater prawn,Macrobrachium rosenbergii

The effect of 5-hydroxytryptamine (5-HT) on larval development of the giant freshwater prawn, Macrobrachium rosenbergii, was investigated. Four days after hatching, larvae were exposed to 5, 50 or 100 μg/ml 5-HT in 12 ppt commercial seawater for a period of 2 or more days. Continuous exposure to 50 μg/ml or 100 μg/ml 5-HT over 2 days reduced the survival significantly and all larvae died by 13 days post-hatch (after 9 days of exposure). On the contrary, there was no significant difference in the survival of larvae exposed to various concentration of 5-HT for 2 days compared to that of the control. Exposure to 5-HT for 2 days stimulated growth and developmental rate of the larvae. Furthermore, pigmentation of the exoskeleton was also induced within 1 h of exposure. The larvae exhibited bright-orange color on their eyestalks, cephalothoraxes and abdomens. Exposure to 100 μg/ml 5-HT for 2 days produced the highest growth, developmental rate and the strongest pigmentation. The average body lengths 25 days post-hatch of larvae exposed to 50 μg/ml and 100 μg/ml 5-HT for 2 days were 3.5 ± 0.6 mm and 4.3 ± 0.7 mm, respectively, compared to 2.8 ± 0.4 mm that of the control. Furthermore, the rate of transformation of larvae to postlarvae during 30–40 days post-hatch was significantly higher in those exposed to 50 μg/ml and 100 μg/ml 5-HT compared to that of the control. The present study indicates that brief exposure of early stage larvae to 50–100 μg/ml 5-HT enhances growth, developmental rate and pigmentation of the giant freshwater prawn larvae.     

Comparison of three fish-loading systems to harvest food-size channel catfish (Ictalurus punctatus)

Three fish-loading systems were used to harvest food-size channel catfish (Ictalurus punctatus). Loading rates of equipment and their effect on post-harvest fish survival and weight gain during cool and warm weather were studied.

The turbine pump loading rate (300·7 kg/min) was greater than the lift net (158·00 kg/min) and vacuum pump (54·1 kg/min), while the lift net was greater than the vacuum pump (p < 0·05).

Mean survivals (± SD) for catfish loaded by lift net, turbine pump and vacuum pump from earthen ponds during cool and warm weather were 96·6% (±2·8), 93·9% (±7·4) and 97·7% (±1·1) and 94·0% (±5·7), 85·3% (±8·6) and 89·0% (±12·5), respectively. Mean weight change (± SD) per catfish loaded by the same equipment during cool-and warm-weather tests were −8·2 g/fish (±31·1), −12·4 g/fish (±15·2) and −17·5 g/fish (±19·9), and 67·6 g/fish (±60·6), 33·9 g/fish (±137·4) and 32·4 g/fish (±142·1), respectivley. There were no significant differences among loading systems for survival or mean weight change per fish. The turbine pump is a possible alternative to the traditional life net as a means of loading food-size channel catfish. Further testing on commercial catfish farms is required.     

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.     

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.     

Formalin as an alternative to trifluralin as prophylaxis against fungal infection in mud crab Scylla serrata (Forsskål) larvae

The toxicity of formalin and trifluralin to the larval stages of the mud crab Scylla serrata was compared in a static bioassay. Prophylactic doses of 5, 10, 15, 20 and 25 μg L⁻¹ formalin and 0.05, 0.1, 0.2, 0.4 and 0.8 μg L⁻¹ trifluralin were used. Toxicity was assessed on the basis of survival of larvae after 24, 48, 72 and 96 h exposure to the test chemicals and metamorphosis to the next larval stage. Result shows that larval survival in all stages was significantly reduced at concentrations of 20 and 25 μg L⁻¹ formalin whereas larvae were able to tolerate all trifluralin treatments. However, larvae became more tolerant to high formalin concentrations as the larval stage progressed. Survival was better at 5, 10 and 15 μg L⁻¹ formalin and in all trifluralin treatments than the control in almost all the larval stages. Faster metamorphosis was observed at 5 and 10 μg L⁻¹ formalin and 0.05, 0.1 and 0.2 μg L⁻¹ trifluralin concentrations. Doses of formalin and trifluralin obtained from the toxicity experiments were applied as prophylaxis to newly hatched larvae in white plastic basins. Prophylactic doses of 5 and 10 μg L⁻¹ formalin and 0.05 and 0.1 μg L⁻¹ trifluralin applied every other day were found to be effective in enhancing survival and larval development to megalopa compared with control. However, no megalopae survived to crab instar in all formalin treatments. Although the use of fungicides in rearing systems resulted in higher survival compared with controls, other strategies (i.e. maintenance of good water quality and hygienic practices in the hatchery) should be further investigated as an alternative to the use of chemicals in hatcheries.     

Salinity tolerance of cultured Eurasian perch, Perca fluviatilis L.: Effects on growth and on survival as a function of temperature

Eurasian perch is generally only considered to be a candidate for freshwater aquaculture even though wild populations are found in estuarine and brackish water habitats. Little knowledge exists on two issues a) the effect of temperature on the salinity tolerance of perch and b) the long-term effects of brackish water on their overall growth performance. The present study addresses these two questions.

Firstly, the effect of temperature (12, 15, 20 and 25°C) on perch survival of a salinity challenge at either 13 or 18‰ was determined. Survival was unaffected by 13‰ at the two lowest temperatures whereas higher temperature and higher salinities had a dramatic detrimental effect (at 25°C, 50% mortality was reach at 62h and 39h for 13‰ and 18‰, respectively). Secondly, we examined the effect of salinity on growth, which was assessed by measuring standard length and body weight at regular intervals for 130days. In addition, Specific growth rate (SGR), Fulton's condition factor (K) and food conversion ratio (FCR) were also calculated as was the effect of salinity on plasma osmolality, blood ion content (Na⁺, Cl⁻, K⁺) and muscle water content at the termination of the experiment. The optimum growth for this study was seen in the lowest salinities at 0 and 4‰. Surprisingly, even small increases in salinity were detrimental to perch growth. At 10‰, growth in terms of body weight was reduced by about 50% after 130days compared to perch reared in freshwater.

Interest in brackish water production of perch would be most likely served best by selecting a strain of perch that is adapted to saline conditions, as found in the lower Baltic region. Further studies are required to understand the potential for brackish water perch production.     

Effects of temperature, salinity and pH on larval growth, survival and development of the sea cucumber Holothuria spinifera Theel

For large-scale seed production of sea cucumbers through a hatchery system, it is imperative to know the effects of environmental parameters on larval rearing. Auricularia larvae (48 h post-fertilization) were obtained from induced spawning of Holothuria spinifera and used in experiments to ascertain the effects of temperature, salinity and pH on the growth and survivorship of the larvae. The larvae were reared for 12 days at temperatures of 20, 25, 28 and 32 °C; salinities of 15, 20, 25, 30, 35 and 40 ppt; and pH of 6.5, 7.0, 7.5, 7.8, 8.0, 8.5 and 9.0. The highest survivorship and growth rate and fastest development of auricularia indicated that water temperature of 28–32 °C, salinity of 35 ppt and pH of 7.8 were the most suitable conditions for rearing larvae of H. spinifera.     

Influence of light intensity on feeding, growth, and early survival of leopard coral grouper (Plectropomus leopardus) larvae under mass-scale rearing conditions

This study investigated the effect of different light intensities on feeding, growth and survival of early stage leopard coral grouper Plectropomus leopardus larvae. Four different light intensities (0, 500, 1000 and 3000 lx) were used and larvae were kept under constant light conditions from 0 day after hatching (DAH) to 5 DAH. The larvae were fed a small S-type of Thai strain rotifers at a density of 20 individuals/mL from 2 DAH. The number of rotifers in larval digestive organ and total length of larvae were examined at 3 h intervals between 04:00 and 22:00 h on 3 DAH, and thereafter at 6 h intervals until the end of the experiment (5 DAH). Four experimental trials of the larval rearing were repeated using by 60 kL mass-scale rearing tanks. The results indicate that coral grouper larvae are visual feeders and their food intake increases with increasing light intensity. Food intake of larvae reared at 3000 lx was significantly higher than those reared at 0–1000 lx on 3 DAH despite being the first-feeding day (P < 0.01). On 4 DAH, total length of larvae reared at 3000 lx was significantly larger than those reared at the lower light intensities (0, 500 and 1000 lx), and thereafter light intensity significantly influenced larval feeding and growth until the end of the experiment. Survival on 5 DAH did not show a significant difference between light intensities, but survival rate at 3000 lx and 1000 lx had a tendency to be higher than those reared at the lower light intensities (0 and 500 lx). In contrast, larvae reared at 0 lx exhibited stagnant and/or negative growth. These results indicate that light intensity is significantly the factor affecting larval feeding, growth, and survival in coral grouper larvae under the rearing conditions.     

Beneficial effects of n-3HUFA enriched Artemia as food for larval palmetto bass (Morone saxatilis × M. chrysops)

The beneficial effects of feeding n−3 highly unsaturated fatty acids (HUFA ≥ 20 carbon fatty acids with three or more double bonds) to palmetto bass (striped bass × white bass) larvae, 4–30 days of age, were studied using Artemia diets enriched with six n-3HUFA levels. Dietary n-3HUFA concentrations were < 0.03% (control diet), 0.33%, 0.63%, 0.87%, 1.26%, and 2.27% of dry-wt Artemia. Larval n-3HUFA contents were reduced at a faster rate with decreasing dietary n-3HUFA intake, and were significantly different by 30 days posthatch (4–20 mg g⁻¹ dry-wt fish). Starved larvae selectively conserved endogenous n-3HUFA reserves, indicating an essential role of n-3HUFA in larval development. Mass mortality in the control and 0.33% n-3HUFA diets occurred at metamorphosis (26–28 days posthatch). At harvest, all fish, except those fed the two highest n-3HUFA diets, suffered from handling stress (shock syndrome) with increasing severity (25 to 100%) at decreasing dietary n-3HUFA intake. Recovery from shock syndrome was 100% at the 0.63% and 0.87% n-3HUFA diets, 63% at the 0.33% n-3HUFA diet and 0% at the control diet. Post-harvest survival was similar among the four highest dietary n-3HUFA groups (64–73%), whereas the two lowest n-3HUFA groups differed significantly (0 and 37%). Growth promotion was evident with increased dietary n-3HUFA intake as fish fed the highest n-3HUFA diet were twice the size of those fed the control diet (99 vs 52 mg wet-wt). Final fish sizes at the three highest n-3HUFA diets were similar. Given similar culture conditions, a minimum dietary n-3HUFA intake of 1.26% of dry-wt Artermia is recommended to avoid handling stress and promote growth in larval palmetto bass.     

Effects of temperature and lipid droplet adherence on mortality of hatchery-reared southern hake Merluccius australis larvae

Effects of exogenous (water temperature) and endogenous (lipid droplet adherence) factors were experimentally tested on early survival of southern hake Merluccius australis reared under controlled conditions. Experiments to determine the effect of temperature (10, 12 and 14 °C) on larval growth rates and yolk-sac absorption rates of unfed southern hake were carried out under laboratory conditions. There was no significant differences in growth rates at the temperature range tested (ANCOVA, F = 0.164, p > 0.25), but yolk-sac absorption rates and mortality increased with temperature (ANCOVA, F = 53.84, p < 0.001). A high percentage (between 31 and 81%) of hake eggs showed a lipid droplet not adhered (i.e., freely moving in the yolk, and not located in the posteriormost portion of the yolk-sac). In a second experiment, fed southern hake larvae with the lipid droplet not adhered during embryonic development did not survive after yolk-sac absorption. This study provides the first data on the influence of the lipid droplet absorption on larval survival of cultured hake, and can be used as an early indication of the quality of the batch.