The effects of elevated pCO2 on growth,shell production and metabolism of cultured juvenile abalone,Haliotis iris

Reduced seawater pH and elevated pCO₂ are important considerations in tank‐based abalone aquaculture, while sea‐based farms may be at risk to ocean acidification reductions in pH. Juvenile Haliotis iris (5–13 and 30–40 mm shell length) were reared in two, 100‐day experiments at ambient pH_nbs (~ 8.1, 450 μatm CO₂), pH 7.8 (~1000 μatm CO₂) and pH 7.6 (~1600 μatm CO₂). Seawater pH was measured and adjusted automatically by bubbling CO₂ into water in replicated flow through tanks. Two separate trials were run, in winter (8.8°C) and summer (16.5°C). Survival and growth were monitored every 30 days, and post experiment measurements of morphometrics and respiration rate undertaken. Growth of shell length and wet weight were negatively affected by reduced pH, with a 2 to 3‐fold reduction in growth of both size classes between ambient and pH 7.6 treatments in the summer experiment. For small juveniles, growth reductions were in conjunction with decreases to shell weight, while large juveniles showed greater resilience in shell production. No changes to respiration rate occurred, suggesting that juveniles may maintain physiological functioning while tolerating dissolution pressure or that they are unable to upregulate metabolism to compensate for pH effects. These data show that CO₂ driven reductions in pH can impact growth, metabolism and biomineralization of abalone, and indicate that water quality and ocean acidification are of importance in aquaculture of the species.     

Effect of Hybrid Abalone,Haliotis discus hannai × Haliotis discus discus,Cultivation on the Carbon Cycle: Carbon Source/Sink

Respiration, calcification, and bio‐deposition of hybrid abalone, Haliotis discus hannai × Haliotis discus discus, fed on different foodstuffs have been measured to evaluate the effect of hybrid abalone culture on carbon source/sink in coastal areas. Fed with Laminaria japonica, Undaria pinnatifida, Gracilaria lemaneiformis, U. pinnatifida, and Ulva pertusa, alternated mutually, the carbon bio‐deposition rate of hybrid abalone was 24.29 ± 6.39, 65.40 ± 10.55, 21.48 ± 5.99, and 29.28 ± 6.47 µg/g/h, respectively. Hybrid abalone fed on U. pinnatifida had a higher carbon bio‐deposition rate compared to that fed on other foodstuff (P < 5%). Rate of CO₂ released by respiration of hybrid abalone fed on the experimental foodstuff was 24.53 ± 8.57, 32.73 ± 7.99, 29.31 ± 6.39, and 33.67 ± 12.37 µg/g/h, respectively. Results indicated that calcification presented less relationship with body weight type of the foodstuff. The rate of CO₂ released by calcification into seawater and atmosphere was 2.77 ± 1.89 and 6.53 ± 3.36 µg/g/h, respectively. The total rate of CO₂ released because of bio‐deposition, respiration, and calcification processes was 16.19 ± 4.67 µg/g/h, while the total rate of carbon sequestered in shells and tissues was 8.94 ± 2.07 µg/g/h. The study revealed that hybrid abalone culture is a source of CO₂.     

Breeding and larval rearing of the camouflage grouper Epinephelus polyphekadion (Bleeker) in the hypersaline waters of the Red Sea coast of Saudi Arabia

This is the first report on the successful year-round natural spawning and larval rearing of Epinephelus polyphekadion (Bleeker) in captivity and under hypersaline water conditions of 42-43%₀ salinity in the Red Sea coast of Saudi Arabia. Although the fish spawned naturally once or twice a year during 1992-94 culture period, incorporation of cod-liver oil in the broodstock diet during the 1995 culture period enabled the fish to spawn continuously for 2-3 days in each month during March, April, May and August. The egg fertilization and hatching rates also increased during the 1995 spawning period. The egg fertilization rate varied from 90 to 100% with a mean of 96.5 ± 3.38%. The egg hatching rate varied from 70 to 95% with a mean of 83.1 ± 10.12%. The fertilized egg diameter averaged 757.3 ± 37.36 μm. There was a linear relation between the fertilized egg size and the egg hatching rate. The increase in the hatching rate relevant to the egg size was statistically significant (P < 0.01). The egg development time until hatching lasted for 19 h at 29°C. The newly hatched larval size ranged from 1.55-1.71 mm with a mean of 1.65 ± 0.052 mm in total length. The larval growth was slow in the early stages and the growth curve until metamorphosis showed a curvilinear pattern. Wide variations in larval size, range 22-47 mm with a mean of 33.40 ± 7.01 mm, were observed during the metamorphosis stage at day 50. No significant difference (P > 0.05) in growth and survival was observed between the larvae reared using white and grey coloured tanks. The larval survival up to metamorphosis was 1.6-4.7% with a mean of 2.98 ± 1.56% in the grey coloured tanks and 1.6-1.9% with a mean of 1.73 ± 0.16% in the white tanks. The results demonstrated the possibility of breeding E. polyphekadion under captive culture conditions. However, methods to improve the larval survival have to be pursued further for commercial farming of this species.     

Acidified seawater suppresses insulin‐like growth factor I mRNA expression and reduces growth rate of juvenile orange‐spotted groupers,Epinephelus coioides (Hamilton, 1822)

Ocean acidification, resulted from high level of carbon dioxide (CO₂) dissolved in seawater, may disturb the physiology of fish in many ways. However, it is unclear how acidification may impact the growth rate and/or growth hormones of marine fish. In this study, we exposed juvenile orange‐spotted groupers (Epinephelus coioides) to seawater of different levels of acidification: a condition predicted by the Intergovernmental Panel on Climate Change (pH 7.8–8.0), and a more extreme condition (pH 7.4–7.6) that may occur in coastal waters in the near future. After 6 weeks of exposure, the growth rates of fish in pH 7.4–7.6 were less than those raised in control water (pH 8.1–8.3). Furthermore, exposure at pH 7.4–7.6 increased blood pCO₂ and HCO₃^? significantly; exposure at pH 7.8–8.0, meanwhile, did not affect acid–base chemistry. Moreover, exposure to pH 7.4–7.6 resulted in lower levels of hepatic igf1 (insulin‐like growth factor I) mRNA, but did not affect levels of pituitary gh (growth hormone) or hypothalamus psst2 and psst3 (prepro‐somatostatin II and III). The results show that highly acidified seawater suppresses growth of juvenile grouper, which may be a consequence of reduced levels of IGF‐1, but not due to diminished growth hormone release.     

Elevated CO2 does not exacerbate nutritional stress in larvae of a Pacific flatfish

Multiple aspects of climate change are expected to co‐occur such that ocean acidification will take place in conjunction with warming and a range of trophic changes. Previous studies have demonstrated that nutritional condition plays a significant role in the responses of invertebrates to ocean acidification, but similar studies have yet to be conducted with marine fishes. In this study, we examined the potential interactive effects of elevated CO₂ levels and nutritional stress on the growth and development of northern rock sole (Lepidopsetta polyxystra). Separate experiments examined the effects of these two environmental stressors during the pre‐flexion (3–31 days) and post‐flexion (31–87 days) larval stages. In both stages, the larval feeding regime has a much larger impact on growth rates than did the CO₂ level, and there was no observed interaction between stressors. By 31 days post‐hatch, larvae in the high‐feeding treatment were 84.2% heavier than the fish in the low‐feeding treatments, but there was no significant effect of CO₂ level on body size or condition. While overall growth rates were faster during the pre‐flexion stage, the effects of food limitation were greater for post‐flexion larvae undergoing metamorphosis, with the high‐feeding treatment fish being 3.3 times as heavy as fish in the low‐feeding treatments. These results have important implications for understanding the impacts of the multi‐faceted nature of climate change on population productivity of commercial fish species in the North Pacific.     

Is batch variability in hatching time related to size heterogeneity and cannibalism in pikeperch (Sander lucioperca)?

Larval size heterogeneity is known to induce cannibalism, and procedures to avoid larval size differences are consequently implemented already during egg incubation and hatching. We investigated the relation between larval development variability, size heterogeneity and cannibalism in pikeperch. Larvae were sorted into five groups according to the time of hatching during a 65‐h period. The larvae with different times of hatch were then reared separately or together during an 18‐day period. Late hatched larvae were longer (P=0.003) and had less yolk remaining (P<0.001) than early hatched individuals at the time of hatching. However, on 11 days post fertilization, the late‐hatching larvae tended to have larger yolk reserves than earlier hatched individuals (P=0.07). Furthermore, the next day, a lower proportion in the late fraction had switched to exogenous feeding (P=0.024). That larvae with a late hatching time developed slower suggests a positive relationship between the hatching time and the embryonic developmental rate. However, differences in the length and available yolk reserves at hatching between larval fractions with different hatching times suggest that hatching is not strictly associated with a specific developmental stage, and that factors other than the development rate of the embryo are involved in the timing of hatching.     

Triploidy induction in Australian greenlip abalone Haliotis laevigata (Donovan) with cytochalasin B

Triploid induction in Australian greenlip abalone, Haliotis laevigata (Donovan), was conducted by blocking the formation of the second polar body using cytochalasin B (CB). Twenty minutes after fertilization, the zygotes of greenlip abalone were treated with four CB concentrations (0, 0.25, 0.5 and 0.75 mg L⁻¹) for 10, 15 and 20 min. The ploidy of resultant larvae was determined using flow cytometry at 72-h post fertilization. Our study showed that fertilization, hatching, survival and induced triploidy of abalone larvae were significantly affected by the CB concentration and treatment duration. The effective range of CB concentration for triploid induction on greenlip abalone was 0.5–0.75 mg L⁻¹ with an induction duration of 10–15 min. The results indicate that the most effective treatment combination for triploid induction in greenlip abalone is 0.5 mg CB L⁻¹ for 15 min starting at 20-min post fertilization.     

Feeding early larval stages of fire shrimp Lysmata debelius (Caridea, Hippolytidae)

An important constraint to the commercial rearing of the marine ornamental shrimp Lysmata debelius is high larval mortality during early stages due to inappropriate procedures of larval collection and not feeding a live prey before one day elapsed after hatching. This incorrect feeding practice is commonly adopted in larval rearing of L. debelius and other ornamental marine shrimps because it is wrongly assumed that reserves of the newly hatched are enough for the first 24 h of life. Present work demonstrates that captive newly hatched L. debelius larvae ingest microalgae within minutes after hatching. When fed solely with Artemia nauplii, they have acceptable survival rates with stocking densities at or below 50 larval L^–1; but when nauplii are combined with microalgae, survival is further improved to zoea 2 as initial mortality is reduced, and higher stocking densities are supported (up to 75 larvae L^–1). The microalgae used were Rhinomonas reticulata, Skeletonema costata and Tetraselmis chuii. Higher survival through metamorphosis to zoea 2 was always observed for groups fed combinations of microalgae including Tetraselmis chuii. It is recommended that, larval collection methods ensure that larvae are fed microalgae within 2–3 h of release.     

Exterminating Sunamphitoe namhaensis using carbon dioxide in seawater for culturing brown algae Sargassum horneri seedlings

The amphipod Sunamphitoe namhaensis grazes on seedlings of Sargassum horneri in culture. To exterminate S. namhaensis, we immersed them in seawater with dissolved carbon dioxide—a treatment used previously to remove copepods in cultures of abalone and sea cucumber. Experiments were conducted under different CO₂ (aq) concentrations and for different lengths of time. Amphipod mortality was 100% following immersion in CO₂ seawater with a CO₂ (aq) concentration of 26,262 µmol/kg (pH 5.0) for 60 min. When algal seedlings were immersed in CO₂ seawater under these same conditions, their survival rate and growth were not affected.

     

The effects of elevated concentrations of dissolved inorganic phosphate in seawater on the growth and survival of juvenile abalone,Haliotis iris

Seawater sampling from three abalone farms in New Zealand showed average ambient concentrations of dissolved inorganic phosphate (P_i) varying between 2.36 and 238 μM. The P_i concentration within each system appeared to be directly linked to the percentage of water that was replaced each day. An experiment was conducted over 5 months to examine the effect of elevated P_i concentrations on the growth of two juvenile abalone (Haliotis iris) size classes (small: average shell length=23.9 ± 0.1 and large: average shell length=61.9 ± 0.1 mm). Abalone from each size class were exposed to P_i concentrations of; (a) natural incoming seawater (average 0.12 ± 0.12 μM), (b) 10.7 ± 1.3 μM, (c) 60.9 ± 5.8 μM and (d) 113.1 ± 5.6 μM. The results suggest that over the course of the 5‐month period of this experiment there was a significant negative impact on growth (shell length and wet weight) when the smaller size class of abalone were exposed to P_i concentrations greater than 10.7 μM and for the large size class of abalone when exposed to greater than 60.9 μM P_i. However, elevated P_i concentrations did not significantly impact on abalone survival during the course of the experiment.     

Drinking activity of the newly hatched larvae of codGadus morhua L.

The drinking rate of cod larvae 1–7 days post hatching was measured from the uptake of³H-labelled dextran (MW = 70000) admixed in the incubation seawater (34 ppt 5°C). The drinking rate increased gradually from 0.15% to 0.59% of the larval body weight on day 1 and day 7 respectively. This increase in drinking rate correlated with an observed decrease in the volume of the yolk sac and its water store. Autoradiographs showed the labelled dextran to be confined to the intestine. Electron micrographs showed an open mouth communicating with the oesophagus and the intestine in cod larvae at the time of hatching. Chloride cells were present on the opercular folds but not on the vestigial, developing gills. The data indicate that the water acquisition mechanism of larval cod is similar to that of adult marine fish.     

Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising

Mariculture of the economically important seaweed will likely be affected by the combined conditions of ocean acidification that resulting from increasing CO₂ rising and decreased light levels, especially under high culture intensity and high biomass accumulation. To examine this coupling effect on the photosynthetic performance of Sargassum fusiforme seedlings, we cultured seedlings of this alga under different light and CO₂ levels. Under low light conditions, elevated CO₂ significantly decreased the photosynthesis of S. fusiforme seedlings, including a decreased photosynthetic electron transport rate. Seedlings grown under the low light intensity exhibited higher photosynthetic rates and compensation irradiance, and displayed higher photosynthetic pigment contents and light absorption than seedlings grown under high light intensity, providing strong evidence of photosynthetic acclimation to low light. However, the captured light and energy were insufficient to support photosynthesis in acidified seawater regardless of increased dissolved inorganic carbon, resulting in declined carbohydrate and biomass accumulation. This indicated that S. fusiforme photosynthesis was more sensitive to acidified seawater in its early growth stage, and strongly affected by light intensity. Future research should evaluate the practical manipulation of biomass accumulation and mariculture densities during the early culture period at the CO₂ level predicted for the end of the century.     

Studies on the artificial propagation of Monopterus albus (Zuiew)

Artificial propagation of Monopterus albus (Zuiew) was conducted during their spawning season in the present study. Different doses of luteinizing-hormone-releasing-hormone analogue (LHRH-A) were tested for inducing the ovulation of brood females. No significant difference was found in the degree-hours and fertilization rates between three different doses (0.1, 0.2 and 0.3 μg LHRH-A g^-1 fish). A fertilization solution of 0.3% NaCl produced significantly higher fertilization rates than the other three solutions (0.5% NaCl, 0.65% NaCl and water). Fertilization times ranging from 5 to 2 0 min gave no significant difference in the fertilization rates. The embryonic and larval development of M. albus was observed and illustrated. The hatching time of eggs of M. albus was about 140 h in the 28-3 0^oC water temperature range. Using Tubifex spp. for the first food for the larval nursery gave higher growth rate than two other foods, zooplankton and artificial food.     

Larval calcification and growth of veligers to early pediveliger of the queen conch Strombus gigas in mesocosm and laboratory conditions

The goals of this study were to evaluate growth, development, and calcification process of veligers of Strombus gigas grown in natural conditions in mesocosm versus laboratory conditions. In this study, larvae bred in mesocosm conditions had a good growth rate (33.3±12.40 μm.day^?1) when fed with natural phytoplankton in natural flowing seawater versus a lower growth rate of 8.8±5.20 μm.day^?1 for larvae reared in laboratory conditions and fed with a monoalgal diet of Nannochloropsis oculata. Physicochemical parameters did not explain the difference on larval growth in both culture systems according to the principal component analysis done. Raman microspectrometry carried out on conch larvae grown in mesocosm and lab conditions allowed us to emphasize the biosynthesis of calcium carbonate species and their structure type evolution (amorphous, aragonite, or calcite structure) as a function of the breeding time by detecting and identifying in the spectra the characteristic Raman bands of CO₃ chemical groups and lattice vibrations. This analytical method seems to indicate that crystalline CaCO₃ structures are not detected in the recorded spectra on larvae reared in laboratory conditions during the early stages of the shell construction of 1 to 8 days. For this reason, light and current flow have also been considered in the discussion that can help to explain the differences found in this study. Contrarily, the Raman spectra acquired on larvae grown in mesocosms exhibit characteristic bands of aragonite (CO₃ double peak at 697–701 cm^?1 and lattice vibrations at 170 and 220 cm^?1) from the third day of breeding. The best shell growth and shell calcification pointed out in larvae grown in mesocosm compared to laboratory conditions are probably due to the nutrient amounts present in the food available in mesocosm.

     

Exploring the potential of providing and feeding pikeperch larvae (Sander lucioperca L.) with euryhaline copepod nauplii: A zoo technical trial

Egg hatching and nauplii success from three euryhaline calanoid copepod species at low salinities suggest a promising alternative initial live feed for pikeperch (Sander lucioperca L.) to the conventional live feed. Acartia bifilosa and Eurytemora affinis are viable candidates with egg hatching down to zero salinity, and Acartia tonsa nauplii survive up to 2 h at zero salinity after transfer from low-salinity seawater. When offered A. tonsa and Artemia, pikeperch larvae equally consumed both prey types. We suggest that euryhaline copepods can be a supplement to or even a substitute for the normal live feed currently used as larval feed for pikeperch.     

Larval growth of turbot, Scophthalmus maximus (L.) produced with fresh and cryopreserved sperm

The present paper assesses the fertilization and hatching rates, as well as the growth, of larvae obtained from four artificial fertilizations (AF) using fresh and cryopreserved sperm of the turbot Scophthalmus maximus (L.). Larvae growth in both sperm groups, measured in terms of length and weight at culture days 0, 7, 14 and 31, are compared, as well as their growth rates. The two groups' fertilization and hatching rates were not significantly different. Likewise, no significant differences in length and wet weight of 7‐ and 14‐day‐old larvae were found using fresh and cryopreserved sperm; however, significant differences were found in 31‐day‐old larvae, which were more attributable to the variability inherent in larval turbot culture, and to variability in the reproductive specimens used in our study, than to the type of sperm employed. These results indicate that the type of sperm used in artificial fertilization, i.e. fresh or cryopreserved, is not a determining factor, either for fertilization and hatching, or for subsequent larval development. Our results also confirm once again the high quality of cryopreserved turbot sperm, and its usefulness in commercial hatcheries.     

The effect of cryoprotectants on the motility and fertilizing capacity of cryopreserved African catfish Clarias gariepinus (Burchell 1822) sperm

The effect of six cryoprotectants was investigated on the cryopreservation of African catfish Clarias gariepinus (Burchell) sperm. Fructose (6%) solution buffered with NaHCO₃‐CO₂ was used as the diluent in the experiments. Glycerol (5–11%), ethylene glycol, methanol and propylene glycol (5–15%) and, finally, dimethyl sulphoxide (DMSO) and dimethylacetamide (DMA) (10%) were tested using various equilibration times (2–30 min). Sperm was frozen in 250‐μL straws in a programmable freezer (Cryocell‐15, BLS, Hungary) from 3 °C to ?4 °C at 4 °C/min and from ?4 °C to ?80°C at 11 °C/min. Thawing was carried out in a 40 °C water bath for 5 s. Fertilization and hatching trials were performed only with DMSO and DMA using 200 and 100 μL of diluted sperm (100 and 50 μL of pure sperm) and the dry and the wet fertilization methods. Ethylene glycol, glycerol, methanol and propylene glycol yielded poor results. An average post‐thaw motility rate of 44.0 ± 9.7% and 22.6 ± 18.1% was achieved after 10 min equilibration using DMSO and DMA respectively. Highest average fertilization (86.8 ± 3.1%) and hatching (67.1 ± 11.9%) rates were achieved with DMA and DMSO, respectively, 200 μL of diluted sperm and the wet fertilization technique. The use of cryoprotectants increased the percentage of malformed larvae compared with the control groups. We found that DMA at a 10% concentration was equally as suitable for the cryopreservation of African catfish sperm as DMSO.     

Preliminary study on the induction of artificial spawning in Haliotis coccinea canariensis Nordsieck (1975)

Induced spawning of Haliotis coccinea canariensis of 29–49 mm shell length was attempted by adding hydrogen peroxide and tris(hydroxymethyl)aminomethane to the seawater. The best spawning rate was obtained at H₂O₂ concentrations of 2, 4 and 8 mmol/l for males and 4 mmol/l for females. The relationships between fecundity and shell length, and between fecundity and body wet weight are exponential and linear respectively. The mean diameters of the fertilized eggs and yolk are respectively 103 and 80 μm. The colour of the eggs is violet. Hatching of trochophore larvae took place 21 h after fertilization at 15°C. At the same temperature veliger larvae settled after 8 days.     

Effect of stocking density and feeding regime on larval growth,survival, and larval development of Japanese flounder,Paralichthys olivaceus,using live feeds

This research examined the effect of initial stocking density and feeding regime on larval growth and survival of Japanese flounder, Paralichthys olivaceus. Larval rearing trials were conducted in nine 50‐L tanks with different initial stocking densities combined with different feed rations (20 larvae/L with standard feed ration [LD], 80 larvae/L with standard feed ration [HD], and 80 larvae/L with four times the standard feed ration [HD+]). Larvae were stocked on 0 days posthatch (DPH) following hatching of the fertilized embryos. Larval total length (TL), survival rates, and final densities were observed on larval settlement (32 DPH) to evaluate larval rearing performance. At 32 DPH, there were no significant differences (p > .05) in TL or survival rates between the LD (46.5 ± 17.0%) and HD+ (40.3 ± 9.4%). The TL and survival rate of HD (23.1 ± 3.5%) were significantly lower than that of LD and HD+ (p < .05). However, the larval density of HD was significantly higher than that of LD (p < .05). HD+ achieved the best larvae production (32.27 ± 7.51 larvae/L), supported by sufficient food source, high water exchange, and proper water quality management (routine siphoning, surface skimming). The larval‐rearing protocols and larval development from hatching to metamorphosis is described in detail, with corresponding photographs taken during the experiment.     

Larval performance of matrinxã, Brycon amazonicus (Spix & Agassiz 1829), after maternal triiodothyronine injection or egg immersion

This study compared the larval performance of matrinxã, Brycon amazonicus, after maternal triiodothyronine (T₃) injection or egg immersion of T₃. In the first experiment, three groups of females (n=4) induced to spawning received pituitary extract (CPE) and a corn oil injection (control), or CPE plus 10 mg or 20 mg kg^?1 bw T₃ dissolved in corn oil (experimental). Larvae were sampled for body weight and length measurement at hatching (0 h) and 12, 24, 36, 48 and 60 h thereafter. Hatching time, hatching success and abnormal development were monitored. In the second experiment, fertilized eggs from four females were immersed in T₃ solutions (0, 0.01, 0.05 and 0.10 mg L^?1) and larvae were sampled at hatching (0 h) and 6, 18, 30, 42, 54, 126 and 198 h thereafter. Hatching time was not affected by either means of hormone treatment. Abnormalities decreased as the T₃ concentration increased in larvae from T₃‐treated broodfish but the number of dead larvae increased proportionally. Larvae from T₃‐injected females had higher weight from 24 h after hatching and greater length from hatching, while the weight of larvae produced from T₃‐immersed eggs changed at 198 h and length from 126 h of rearing. Both routes of T₃ administration affected the early growth of matrinxã but the effect was observed earlier when broodstock females were injected.