Dietary influence on growth and development of flat oyster,Ostrea angasi (Sowerby, 1871), larvae

The influence of algal diet on survival, growth and development of hatchery reared flat oyster, Ostrea angasi, larvae was investigated in a series of uni, binary and ternary algal diet trials. Early stage larvae (140–230 μm shell length) generally grew faster than late‐stage larvae (230–340 μm shell length) when fed unialgal diets. Of the 24 algal diets evaluated, larvae fed unialgal diets of Isochrysis sp. (T. Iso), Nannochloropsis oculata, Tetraselmis chuii or Pavlova lutheri; a binary diet of T. chuii+T. Iso; or ternary diets of T. chuii+T. Iso combined with P. lutheri or N. oculata had the greatest larval growth, survival, development and metamorphosis, in the respective trials. The correlation between growth rate and spat produced in late‐stage larvae was stronger when fed unialgal diets (r = 0.75) than when larvae were fed either binary or ternary diets (r = 0.44 and r = 0.45 respectively). Marked differences in proportion of spat produced (24 h post metamorphosis) were evident among diets producing similar growth rates. For hatchery production of O. angasi larvae, ternary diets of T. chuii+T. Iso combined with either P. lutheri or N. oculata were the best diets to maximize larval growth rate, development and survival 24 h post metamorphosis.     

Influence of feeding regime and temperature on development and settlement of oyster Ostrea edulis (Linnaeus, 1758) larvae

Under controlled conditions of food density and temperature, larval performances (ingestion, growth, survival and settlement success) of the flat oyster, Ostrea edulis, were investigated using a flow‐through rearing system. In the first experiment, oyster larvae were reared at five different phytoplankton densities (70, 500, 1500, 2500 and 3500 μm³ μL^?1: ≈1, 8, 25, 42 and 58 cells μL^?1 equivalent TCg), and in the second, larvae were grown at four different temperatures (15, 20, 25 and 30°C). Overall, larvae survived a wide range of food density and temperature, with high survival recorded at the end of the experiments. Microalgae concentration and temperature both impacted significantly larval development and settlement success. A mixed diet of Chaetoceros neogracile and Tisochrysis lutea (1:1 cell volume) maintained throughout the whole larval life at a concentration of 1500 μm³ μL^?1 allowed the best larval development of O. edulis at 25°C with high survival (98%), good growth (16 μm day^?1) and high settlement success (68%). In addition, optimum larval development (survival ≥97%; growth ≥17 μm day^?1) and settlement (≥78%) were achieved at 25 and 30°C, at microalgae concentrations of 1500 μm³ μL^?1. In contrast, temperature of 20°C led to lower development (≤10 μm day^?1) and weaker settlement (≤27%), whereas at 15°C, no settlement occurred. The design experiments allowed the estimation of the maximum surface‐area‐specific ingestion rate  = 120 ± 4 μm³ day^?1 μm^?2, the half saturation coefficient {X_K} = 537 ± 142 μm³ μL^?1 and the Arrhenius temperature T_A = 8355 K. This contribution put a tangible basis for a future O. edulis Dynamic Energy Budget (DEB) larval growth model.     

Effects of temperature and photoperiod on the conditioning of the flat oyster (Ostrea edulis L.) in autumn

The production of the flat oyster Ostrea edulis (L.) natural spat in Europe has decreased almost by 60% in the past ten years. Thus, the importance of the production of oyster spat in hatcheries is evident. One of the critical steps in hatchery production is broodstock conditioning, especially difficult in autumn, when gonadal development is in resting period. Conditioning is influence by temperature, photoperiod and nutrition. In this work, the effects of two temperature and three photoperiod regimes on the conditioning of O. edulis were studied for three years by stereological analyses and registering number and dates of spawning and larval yield. Temperature had a positive effect on the gonadal development of O. edulis during conditioning. The percentages of germinal cells in oysters conditioned with a gradient of temperature (14–18°C) were double compared to oysters conditioned at 15°C. Oysters conditioned with longer photoperiods showed higher percentages of germinal cells. There was no interaction between temperature and photoperiod. Spawning was observed in the oysters treated with daylight (8–16 h) ten weeks from the beginning of conditioning. Flat oysters conditioned with 8 h and 8–12 h of daylight delayed the first spawning for a month. Total larval production was higher in the oysters treated with the longest daylight gradient. Gonadal and gametogenic development was a non‐synchronic process and the spawning extended for around two months. A protocol for flat oyster broodstock conditioning in autumn by using both a gradient of temperature (14–18°C) and daylight (8–16 h) is proposed.     

Conditioning of the European flat oyster (Ostrea edulis,Linnaeus 1758): effect of food ration

To establish a reliable protocol for the broodstock conditioning of the oyster Ostrea edulis (Linnaeus 1758) in hatcheries is important to obtain the best number of viable larvae all year even outside the natural season for maturation and spawning. Hatchery production of bivalves depends on their initial gonadal maturation state, which is linked to season and several other factors, such as temperature, daylight, salinity and food supply. Ration and diet composition are important in broodstock conditioning because food availability affects fecundity and gametogenic development. In this work, the effect of food ration on O. edulis conditioning was studied in autumn and winter. The results of this study showed that the broodstock conditioned with a food ration of 6% and 9% produces the highest number of larvae in autumn and winter. These food rations produced rapid gonadal development and larval release in a short period with a similar larval production. The oysters conditioned with a food ration of 3% delayed larval release and produced a significantly lower number of larvae in autumn. In the 9% ration treatment, the percentages of mortality were significantly higher in both autumn and winter. Thus, a 6% food ration is likely to be the most suitable for flat oyster conditioning combined with a gradient of temperature (14–18°C) and a gradient of daylight (8–16 h).     

The effects of stressors on the dynamics of Bonamia exitiosus Hine, Cochennec-Laureau & Berthe, infections in flat oysters Ostrea chilensis (Philippi)

Oysters, Ostrea chilensis, infected with Bonamia exitiosus were held under stressful conditions for 14 days, and then under normal conditions for 3.5 months, to determine the affects of stress on B.exitiosus infection levels. The stressors used were (1) air exposure for 8 h daily; (2) hot water (25–26 °C), or (3) cold water (7 °C) for 1 h daily; (4) hyposaline (15‰), or (5) hypersaline (39–40‰) water; (6) starvation in filtered sea water; and (7) vigorous stirring four times a day. A control tank held oysters in static sea water, which was changed daily. Oysters were also (8) kept in a trough among heavily infected oysters (trough exposure), or (9) in a trough without other oysters (control), for 4 months. Oysters in hyposaline conditions all died within 3 weeks, but this was apparently unrelated to Bonamia infection. Otherwise, cumulative mortalities were highest in trough exposure, cold, hypersaline and hot treatments. There was a significant difference in prevalence between treatments, and the stir, hot, cold, hypersalinity and trough exposure treatments had significantly higher intensities of infection than controls. The mean intensity of Bonamia infection was significantly higher among female and spent oysters than in male and hermaphrodite oysters.     

Quantitative dietary leucine requirement of juvenile Pacific white shrimp,Litopenaeus vannamei (Boone) reared in low‐salinity water

The experiment was conducted to determine the leucine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low‐salinity water (0.50–1.20 g L^?1). Six diets were formulated to contain 410 g kg^?1 crude protein with fish meal, peanut meal and precoated crystalline amino acids with different concentration of l ‐leucine (16.72, 19.60, 22.06, 24.79, 27.28 and 30.16 g kg^?1 dry diet). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.38 ± 0.002 g), and the feed trial lasted for 8 weeks. The results indicated that the maximum weight gain was observed at 24.95 g kg^?1 dietary leucine group, whereas the diets containing higher leucine concentration conversely reduced the growth performance (P < 0.05). Moreover, the highest body protein content and body protein deposition and the lowest haemolymph AST and ALT activities were also found at 24.95 g kg^?1 dietary leucine group. With the increase in leucine in diets, a dose‐dependent increase was found in body lipid content and haemolymph urea concentration. The polynomial regression calculated using weight gain, feed efficiency and body protein deposition indicated that the optimal dietary leucine requirement for L. vannamei reared in low‐salinity water was 23.73 g kg^?1 leucine of dry diet, correspondingly 57.88 g kg^?1 of dietary protein.     

Combined effects of temperature and salinity on yolk utilization in Nile tilapia (Oreochromis niloticus)

The combined effects of temperature and salinity on the yolk utilization of sac fry in Nile tilapia (Oreochromis niloticus) were investigated using central composite experimental design and response surface approach. Based on the preliminary trials, temperature was determined to range from 22 to 34°C, and salinity ranging from 2 ppt to 10 ppt. The utilization was mensurated in terms of yolk sac volume. Results showed that the linear effects of temperature and salinity on the yolk utilization was significant (P < 0.01); the quadratic effects of and the interaction between the two factors were significant (P < 0.05); temperature was more important than salinity in influencing the yolk utilization. The model equation of yolk sac volume towards temperature and salinity was established. From those high R² values, the model had excellent goodness of fit to experimental data and could be applied for predictive purpose. What with the production cost, it is suggested that the temperature/salinity combination, i.e. 28–30°C/4–6 ppt, be employed during the period of sac fry rearing, in which the yolk utilization was on average 98.6%.     

Effects of temperature,salinity and body size on the physiological responses of the Iwagaki oyster Crassostrea nippona

The physiological responses of the juvenile Crassostrea nippona in terms of filtration, oxygen consumption and ammonia excretion to changes in temperature (16–32°C), salinity (15–35 psu) and body size (small, medium and large) were investigated. In this study, the values of filtration rate (FR), oxygen consumption rate (OCR) and ammonia excretion rate (AER) increased with temperature rising from 16°C to 24°C, reaching the highest values at 24°C and 28°C; with any further increase in temperature above this limit, these values decrease drastically (p < .05). The highest Q₁₀ coefficients were 2.75 for large, 3.54 for medium at 16–20 and 3.47 for small size at 20–24°C respectively. Moreover, the responses of FR and OCR were found to be influenced significantly by salinity, tending to increase concomitantly with salinity up to 25–30 psu, though the values of these parameters were diminished dramatically (p < .05) above this level, showing a reverse pattern from that observed in AER, which firstly decreased to the lowest level at 25 and 30 psu, and then severely (p < .05) increased to the highest level at 35 psu. In addition, the low O:N ratios of all sizes of C. nippona at 16°C and 30–35 psu were indicative of a protein‐dominated catabolism, whereas the O:N ratios of large size at 20–32°C and all sizes at 20–30 psu, indicating that the metabolic energy from protein diminished and lipid and carbohydrate were used as the energy substrates. Physiological rates of C. nippona were well correlated with its size. The average values of mass exponents (b‐values) estimated in the present study were 0.657 for OCR and 0.776 for AER at different temperatures, and 0.647 for OCR and 0.767 for AER at varying salinities, signifying that physiological process of C. nippona becomes relatively slower with increasing body size regardless of temperature or salinity. Finally, our results confirm that the optimal temperature and salinity for juvenile C. nippona lie within 24–28°C and 25–30 psu respectively. The results of physiological traits in response to environmental factors of this species are informative in site selection for the cultivation.     

Effect of temperature on survival,growth and development of Mytilus galloprovincialis larvae

Mussel aquaculture is widely prevalent worldwide, but generally relies on natural seed collection, which does not always meet the needs of the producers. Thus, development of mussel hatcheries is of economic interest in some parts of the world, such as Europe; it provides opportunities not only on annual reliability of seed but also on genetic improvements. To broaden knowledge on mussel larval physiology, we carried out temperature treatments (17, 20 and 24 °C) on Mytilus galloprovincialis larvae under laboratory conditions. The trials ended when 30% of the larval population was in the post‐larval stage. The temperature coefficient Q₁₀ indicated a strong relationship between temperature and increase in growth from 17 to 20 °C, but not between 20 and 24 °C. Exposure of M. galloprovincialis larvae to 17 °C resulted in poor growth, low survival and a delayed development and was considered to be inadequate for M. galloprovincialis larval culture. Rearing the larvae at 20 or 24 °C produced better growth, higher survival rates and faster metamorphosis as compared with 17 °C. The temperature region within 20 and 24 °C was suggested as adequate for the mussel M. galloprovincialis larval culture, and implications of these results on the development of commercial hatcheries were discussed.     

Effect of incubation temperature on the embryonic development and yolk‐sac larvae of the Pacific red snapper Lutjanus peru (Nichols & Murphy, 1922)

The effect of incubation temperature on embryonic development and yolk‐sac larva of the Pacific red snapper Lutjanus peru were evaluated by testing the effect of 26, 28 and 30°C, as this is the natural thermal interval reported during the spawning season of Pacific red snapper in the Gulf of California, Mexico. Sixteen developmental stages were observed. The incubation temperature affected the rate of development and time to hatching, being shorter at 30 than at 26°C, but no significant effect (P < 0.05) on larval length at hatching was registered. The depletion rate of yolk sac and oil globule was affected by incubation temperature particularly during the first 12 h post hatching (hph). At the end of the experiment (48 hph), significantly (P < 0.05) larger larvae were recorded at 26°C (TL = 3.22 ± 0.01 mm) than at 28° (TL = 3.01 ± 0.02 mm) and 30°C (TL = 2.97 ± 0.05 mm). Incubation of newly fertilized eggs at 26°C produces larger larvae, which may help to improve feeding efficiency and survival during first feeding.     

Reproductive success under the joint influences of temperature and salinity in noble scallop,Chlamys nobilis (Reeve)

In this study, the joint effects of two important environmental factors, temperature and salinity, on the per cent fertilization (FR) and per cent hatching (HR) of noble scallop, Chlamys nobilis, was evaluated using the central composite design and the response surface methodology. The results showed that the linear effects of temperature on FR and HR were significant (P < 0.01), and the linear effects of salinity were non‐significant (P > 0.05); the interactions between temperature and salinity were not significant (P > 0.05); the quadratic effects of temperature and salinity on the two responses were significant (P < 0.01); temperature was more important in influencing the reproductive success. The model equations of FR and HR towards temperature and salinity were established, with R² more than 98%, indicating that the models had excellent ability for goodness of fit and projection. Through simultaneously optimizing the two models derived, we found out that the optimum factor combination was 25.7°C/29 ppt and the greatest reproductive success was 89.93% for FR and 72.42% for HR. The desirability value of 97.30% showed the reliability of these optima. Our results provide some valuable guidelines for refining the reproductive efficiency of C. nobilis.     

Efficacy of calcein as a chemical marker of green‐lipped mussel (Perna canaliculus) larvae and its potential use for tracking larval dispersal

An optimal chemical shell marking protocol was developed for the New Zealand green‐lipped mussel, Perna canaliculus with a view to its future use in larval tracking experiments. Larval P. canaliculus aged either 10, 15 or 19 days post fertilization were immersed in treatments of 50, 100 and 200 mg L^?1 of calcein for a period of 24 h before measurements of shell mark brightness were taken. There was 100% marking success in all calcein treatments for all age classes, with 19‐day larvae immersed in 200 mg L^?1 calcein producing the brightest mark. Growth was not affected by calcein immersion; however, 10‐day larvae exhibited significantly higher levels of mortality compared with 15‐ and 19‐day larvae suggesting a reduced resilience to the marking protocols in younger larvae. In a mass staining experiment, a solution of 100 mg L^?1 calcein was used to successfully stain15.6 million hatchery reared P. canaliculus larvae. Calcein, therefore, offers a low impact method with which to stain the sensitive early life stages of this species thus providing a rapid method for identifying individuals of interest, i.e. individuals released in the wild or specific family lines within a hatchery environment.     

Microbial communities associated with early stages of intensively reared orange‐spotted grouper (Epinephelus coioides)

The gut microbiota plays key roles in the health and general welfare of fish larvae, the present study characterized the bacterial communities associated with grouper Epinephelus coioides larvae during a period of 22 days post hatch (DPH) in an intensive hatchery using both cultivation‐based and cultivation‐independent approaches. Both approaches confirmed that bacteria were present in the gut of larvae before and after the onset of exogenous feeding, and the number of cultiviable bacteria increased gradually from 2 DPH to 22 DPH. A more complex bacterial profile was present in larvae fed fertilizer oyster eggs for 4 days (8 DPH), probably as a result of the onset of exogenous feeding. Interestingly, similar internal microbiota were observed in larvae fed fertilized oyster eggs for 4 days (8 DPH) and rotifers for 2 weeks (22 DPH), although different microbial communities were present in the two feeds. This might suggest that the gut environment of E. coioides larvae selects for a common microbiota, which is more closely related with the rearing water than the two feeds. Therefore, bacterial community of the rearing water may play a critical role in the establishment of gut microbiota of fish larvae and more attention should be paid to its practical modulation by using probiotics. In addition, some potentially beneficial bacteria, such as Lactococcus spp., were the major components of the microbiota associated with fertilized oyster eggs, while these bacteria were not detected in larvae samples.     

Year‐round natural spawning,early development,and the effects of temperature,salinity and prey density on captive ornate goby Istigobius ornatus (Rüppell, 1830) larval survival

Natural spawning, early development and larviculture of the ornate goby Istigobius ornatus in captivity were studied for the first time. I. ornatus spawned 46 times from 31 October 2013 to 31 October 2014. Fecundity ranged from 246 to 10,214 eggs per clutch, with an average hatching rate of 77.8% ± 9.9% (M ± SEM). Fertilized eggs (1.31–1.54 × 0.46–0.50 mm in diameter) were adhesive demersal and oval‐shaped. Embryonic development lasted 84 hr at 27.5 ± 0.5°C. Newly hatched larvae [2.12 ± 0.04 mm in total length (TL)] transformed to the juvenile stage completely when TL was 7.79 mm. Effects of different water temperatures (24, 28 and 32°C) and salinities (10, 15, 20, 25, 30, 35 and 40 g/L) on per cent survivals (%) and survival activity indices (SAIs) were tested. Survival was not significantly different under different temperatures; SAIs was significantly higher at 28°C. Larvae showed the significantly higher survival and SAIs at salinities 10–30 g/L than at 35 and 40 g/L. Effect of different prey densities on survival was significantly higher in 7 days post hatch larvae fed 20 and 30 rotifers/ml. These findings could guide future programs in captive breeding technology development and commercial production of other marine ornamental gobies.     

Factors influencing the quality of half‐pearls (mabé) produced by the winged pearl oyster,Pteria penguin (Röding, 1758)

The winged pearl oyster, Pteria penguin, is cultured primarily to produce half‐pearls (mabé). The mabé quality is influenced by culture techniques, but there is limited information in this field. P. penguin with mean (±SE) dorso‐ventral height of 250 ± 6.5 mm were used to investigate the influence of culture period and nucleus position on mabé quality. Oysters were relaxed using 1‐propylene phenoxetol, and five nuclei were glued at different positions to the inner surfaces of the oyster shells; three on the more concave left valve and two on the right valve. Nucleated oysters were then cultured for 10 months under commercial pearl farming conditions at Savusavu in Fiji. Nacre deposited at the base and top of the nuclei was measured monthly, from the 6th to the 10th months of culture and the different qualities of mabé produced at different positions were scrutinized. Nacre thicknesses at the base and top of the resulting mabé were significantly different at different months (P < 0.05) and the rate of nacre deposition was highest during the warmer months. The different positions of nuclei on the valve greatly affected the quality of mabé formed. After a 10‐month culture period, around 1 mm of nacre covered the nuclei although the best quality mabé were obtained after 9 months.     

The effects of constant and oscillating temperature on embryonic development and early larval morphology in longfin yellowtail (Seriola rivoliana Valenciennes)

Constant and oscillating egg incubation temperatures on embryonic development and early larval morphology were studied in longfin yellowtail (Seriola rivoliana Valenciennes). We investigated the effects of constant temperatures from 16 to 32°C on embryo development and larval morphology at hatch, and whether oscillating temperature during embryogenesis could lead to larval morphological variations. After hatching, larval morphology and development during yolk sac (YS) utilization were examined in larvae at constant temperatures and larvae at 25°C that had oscillating temperature during egg incubation. Hatching rates were > 75%, only decreasing to ~ 50% at 30°C. At constant temperatures, the largest larvae occurred at 22 and 24°C. The oscillating temperature did not affect the timing of embryo development but resulted in larger and smaller larvae with a smaller and bigger YS, respectively, with a similar hatching time. Therefore, a growth response occurred in embryos during a window of development before hatching, depending on the adaptive response to temperature (spawn‐specific). After hatching, most of the YS was absorbed within 24 hr in all treatments, and the growth of the larval head was a priority with an optimal development at 26°C. There was compensatory growth in smaller larvae resulting in similar sizes after YS utilization, but larvae showed variations in body structure that could be important in further aquaculture research.     

Different responses between orange variant and cultured population of the Pacific oyster Crassostrea gigas at early life stage to temperature‐salinity combinations

Although breeding of rare shell colour variants has drawn widespread attention from shellfish breeders, the potential disadvantages of their adaptive capacity have been ignored in practice. To explore the difference in adaptive capacity between orange shell variant (OSO) and commercially cultured population (CPO) of the Pacific oyster Crassostrea gigas at early life stage, the development to D‐larvae and larval survival and growth (just 23 and 30°C for larval experiment) of them were compared under different temperature (16, 23 and 30°C) and salinity (17, 25 and 33 psu) combinations. In this study, at 23°C and 25 psu, for both OSO and CPO there was no difference in fertilization rates and survival (p > .05) (mean percentages of D‐larvae after fertilized 40 hr ≥ 95.00%; mean larval survival rates on day 10 > 80.00%). However, the percentage of D‐larvae of CPO at 40 hr was significantly (p < .05) higher than OSO at temperatures of 16 and 30°C and 25–33 psu and 17 psu at 23°C. Similarly, CPO has a better larval survival on day 10 and growth than OSO at salinities of 17 and 33 psu at 23°C. Overall, our results indicate that OSO can have an equally good performance like CPO at early life stage under optimal condition (23°C; 25 psu), but the potential disadvantages in adaptive capacity will be shown at suboptimal conditions. These findings can guide future hatchery breeding of OSO, and suggest the potential disadvantages in adaptive capacity in rare colour variants need more attention in further breeding.     

A production season of turbot larvae Scophthalmus maximus (Linnaeus, 1758) reared on copepods in a Danish (56°N) semi‐intensive outdoor system

Turbot were reared from yolk sack larvae to juvenile in an outdoor semi‐intensive system. Three production cycles were monitored from May to September. A pelagic food chain was established with phytoplankton, copepods and turbot larvae. Abiotic and biotic parameters of lower trophic levels together with turbot larval survival, development, prey electivity and growth were monitored. A decreasing larval survival from 18.4% in May to 13.6% in July and just 7.0% in September was observed. The overall phytoplankton and copepod abundance decreased during the productive season. The turbot larval growth showed significant differences between larvae below (isometric) and above (allometric) 7 mm. Larval fish gut content showed no differences with available prey between production cycles. Therefore, it appears that the available prey concentration is governing their growth in this outdoor system. First‐feeding turbot larvae exhibited active selection for nauplii whereas developed larvae switched to copepodites and adult copepods. Although developing turbot larva exhibited active selection towards copepod size classes, there was no evidence of selective feeding on either of the two dominant copepod species. The turbot larvae's prey ingestion was modelled together with the standing stock of copepod biomass. The model results indicated that the estimated need for daily ingestion exceeded the standing stock of copepods. Hence, the initially established food web was unable to sustain the added turbot larvae with starvation as a consequence. We therefore suggest several solutions to circumvent starvation in the semi‐intensive system.