Hatchery broodstock conditioning of the blue mussel <Emphasis Type="Italic">Mytilus edulis</Emphasis> (Linnaeus 1758). Part I. Impact of different micro-algae mixtures on broodstock performance

Blue mussel (Mytilus edulis) broodstock collected from the Irish Sea during wintertime (November) was conditioned with three different microalgae diets. Positive flagellates (PF) treatment consisted of Pavlova lutherii, Isochrysis galbana (T-Iso), and Chaetoceros calcitrans (1:1:1). Positive diatoms (PD) treatment consisted of Pavlova lutherii, Chaetoceros calcitrans, and Skeletonema costatum (1:1:1). Broodstock animals in the PF and PD treatments were fed a total of 2.4 × 10¹¹ algae cells per day. Animals in the negative flagellates (NF) treatment received only 1/8th of the total amount of algae of the PF diet. The conditioning diets had an impact on spawning success and broodstock fecundity but not on hatching rate, which was similar in all three groups. The best results were obtained with the PD diet where 84% of the conditioned animals spawned and females released 5.0 × 10⁶ eggs on average. Animals belonging to the PF and NF treatments released, on average, only 3.6 × 10⁶ and 1.6 × 10⁶ eggs, respectively. Although the amounts of algae provided to the broodstock animals had no effect on the hatching rate, the D-larvae resulting from the NF treatment were smaller in size than the larvae from the other treatments. Biochemical analysis of the different broodstock groups at the end of the experiment revealed higher carbohydrate levels in group NF than in PF and PD, supporting the theory that gametogenesis is mainly supported by the energy from the glycogen reserves. As far as we are aware this is the first study describing hatchery broodstock conditioning of blue mussels under fully controlled conditions.     

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.     

A physiological and biochemical approach to selecting the ideal diet for Ostrea edulis (L.) broodstock conditioning (part A)

To select the best microalgae for Ostrea edulis conditioning, four single species diets were fed to batches of broodstock, which were then compared using physiological and biochemical approaches. Ingestion and absorption were first studied, showing that Chaetoceros gracilis and Skeletonema marinoï were efficiently ingested (4.9–5.3 mg g^?1 h^?1) and absorbed (1.9–2.5 mg g^?1 h^?1) while Tetraselmis suecica led to the lowest physiological responses (0.36 and 0.12 mg g^?1 h^?1 respectively). When O. edulis were fed any microalgae except T‐ISO with only 79 mg g^?1, gonads accumulated carbohydrates from 116 to 141 mg g^?1 and the extent of accumulation depended on the species supplied in the order T. suecica<C. gracilis<S. marinoï. When oysters were fed either of the diatoms (C. gracilis or S. marinoï), an efficient transfer of 20:5(n‐3) to all tissues, including the gonads, was recorded while no enrichment in 22:6(n‐3) occurred in all tissues (polar fraction) when oysters were fed T‐ISO. In contrast (22:5(n‐6)), a characteristic fatty acid of T‐ISO accumulated in all tissues, confirming its allocation despite particularly low ingestion (1.66 mg g^?1 h^?1) and absorption (0.32 mg g^?1 h^?1). When oysters were fed C. gracilis or S. marinoï an efficient transfer of cholesterol and campesterol from diatoms to the gonads was observed, while no sterol accumulation occurred in the gonad when fed T. suecica. Because of low ingestion, absorption and poor biochemical compounds' transfer, T. suecica is not recommended for O. edulis conditioning. T‐ISO also exhibited low physiological performances but due to a specific 22:6(n‐3) enrichment in the gonad neutral fraction (16.1%), its potential role in reproduction should be considered. Chaetoceros gracilis is highly recommended for O. edulis broodstock while a source of DHA other than that provided by T‐ISO should be found due to its poor absorption. Because a mixed diet has been shown to be more efficient for O. edulis broodstock conditioning, complementary trials dealing with the effects of other species rich in 22:6(n‐3) such as Rhodomonas salina or Pavlova lutheri should be performed.     

Diet trials on tehuelche scallop Aequipecten tehuelchus (d''Orb) larvae

Laboratory spawned one week old veliger larvaeof the tehuelche scallop, Aequipectentehuelchus (D'Orb., 1846), were reared topedivelger stage under three different dietaryregimes in order to determine the best algalcombination under standard hatchery conditions.Veligers were cultured at mean densities of 2.7larvae/ml. Larval growth and survival wereassessed on larvae fed the following dietarytreatments: (1) Isochrysis galbana(T-Iso)+ Chaetoceros calcitrans, (2)Pavlova lutheri + C calcitrans, and (3)P. lutheri + I. galbana T-Iso +Ch. calcitrans. The highest growth rateswere detected on larvae fed diets includingP. lutheri.     

Influence of different microalgal diets on gonadal development of the carpet shell clam <Emphasis Type="Italic">Ruditapes decussatus</Emphasis> broodstock

Studies considering broodstock conditioning of Ruditapes decussatus mostly used flagellates and diatoms for feeding, mainly Isochrysis galbana and Chaetoceros calcitrans, respectively. The present study evaluated the effect of different microalgal diets on gonadic maturation of R. decussatus including three microalgae species (C. calcitrans, Tetraselmis suecica, and Nannochloropsis oculata) which were used to prepare six diets: three monospecific and three bispecific mixed diets at a proportion of 1:1. Clams were daily fed at a ratio of 1% dry weight of algae/live weight of clam and unfed treatment was used as control. Results showed that clams fed C. calcitrans alone or mixed with T. suecica attained earlier full maturity with the highest response to spawning induction (after 34 conditioning days) and largest proportion in the partial spawning phase for both, followed by T. suecica alone after 48 days. In contrast, N. oculata alone or mixed diets demonstrated poor performance for gonadal maturation. Unfed treatment did not show any sign of maturation. The results indicated that T. suecica has high conditioning potential like C. calcitrans and their mixture gave the highest benefit. Therefore, T. suecica can be recommended for R. decussatus broodstock conditioning.     

Proximate and fatty acid composition of the gonads of wild versus hatchery‐conditioned Pinctada margaritifera broodstock

The composition of protein, carbohydrate, lipid and fatty acids of the gonad of wild female broodstock of black‐lip pearl oyster, Pinctada margaritifera, was compared with oysters fed on a ternary combination of microalgae in hatchery. Artificial feeding was found to be as good as natural feeding in terms of number and size of released eggs. Lipid, protein and carbohydrate reserves of unfed oysters were found to be insufficient to complete oogenesis. The proportions of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) of the neutral and polar lipids extracted from female gonads were not influenced by variations in the fatty acid composition of the natural food and ternary combination of microalgae in hatchery. T‐Iso, Chaetoceros calcitrans and Chaetoceros muelleri were able to provide sufficient 22:6n‐3 (DHA) and 20:5n‐3 (EPA), two of the most important essential fatty acids required for gametogenesis. The n‐3/n‐6 and 22:5n‐3/20:4n‐3 ratios were consistently higher in the neutral lipids than in the polar lipids. Conversely, the ratio of 20:4n‐3/20:5n‐3, 22:6n‐3/20:5n‐3 and PUFA/SFA was higher in the polar lipids.     

Insights on the association between somatic aneuploidy and ostreid herpesvirus 1 detection in the oysters Crassostrea gigas,C. angulata and their F1 hybrids

Cytogenetic abnormalities associated with viral infections, including from viruses of the Herpesvirales order, have been reported in vertebrate species. Ostreid herpesvirus 1 (OsHV‐1) has been detected worldwide during mortality outbreaks of the Pacific oyster Crassostrea gigas. On the other hand, a high proportion of aneuploid cells in somatic tissues have been observed in C. gigas. In this study, we analysed the putative association between aneuploidy levels and the detection of OsHV‐1 in gills of C. gigas, the Portuguese oyster C. angulata and their F1 hybrids cultured in Ria Formosa (Portugal). OsHV‐1 was detected by PCR in 5.4% of the total of oysters analysed (n = 111) namely in 11.1%, 8.0% and 1.7% of C. gigas, C. angulata and F1 hybrid respectively. Sequencing analysis of a viral fragment amplified with the C2/C6 primer pair revealed a high similarity with the OsHV‐1 reference type. Moreover, in situ hybridization confirmed the presence of OsHV‐1 in gill tissue. Oysters where OsHV‐1 was detected had a significantly higher mean percentage of aneuploid cells (25%) than the ones where the virus was not detected (18%). However, the overall low percentage of positive samples contrasted with the high mean percentage of aneuploidy observed, with 50% of the oysters analysed showing a percentage of aneuploid cells between 20% and 30%. We hypothesize that somatic aneuploidy may adversely affect oysters making them more prone to OsHV‐1 infection, but the virus is unlikely to be the cause of somatic aneuploidy.     

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).     

Diet trials on tehuelche scallop Aequipecten tehuelchus (d'Orb) larvae

Laboratory spawned one week old veliger larvaeof the tehuelche scallop, Aequipectentehuelchus (D'Orb., 1846), were reared topedivelger stage under three different dietaryregimes in order to determine the best algalcombination under standard hatchery conditions.Veligers were cultured at mean densities of 2.7larvae/ml. Larval growth and survival wereassessed on larvae fed the following dietarytreatments: (1) Isochrysis galbana(T-Iso)+ Chaetoceros calcitrans, (2)Pavlova lutheri + C calcitrans, and (3)P. lutheri + I. galbana T-Iso +Ch. calcitrans. The highest growth rateswere detected on larvae fed diets includingP. lutheri.     

Phenotypic trait of Crassostrea hongkongensis♀× C. angulata♂ hybrids in southern China

The Hong Kong oyster (Crassostrea hongkongensis) and the Portuguese oyster (Crassostrea angulata) are important aquaculture species in southern China. To understand the potential feasibility of hybridization between the two species, two‐by‐two factorial cross‐experiments were conducted in Shenzhen (Guangdong province). An asymmetry in fertilization was revealed: C. hongkongensis eggs could be fertilized by C. angulata sperm, but the reciprocal cross was not possible. The fertilization and hatching success in the C. hongkongensis females × C. angulata males (HA) cross was lower than the two intraspecific crosses. Moreover, hybrid larvae had a slower growth rate than those from parental progenies due to genome incompatibility. However, the size of the spat and adult growth were greater than those of the two parental progeny, with obvious heterosis during the grow‐out stage. The survival advantage of hybrids was examined at all times. The surprising finding was that all hybrids were completely fertile, meaning they could produce normal and functional gametes. Genetic analysis by molecular markers was applied to confirm that the HA spat were true hybrids. Our results revealed that the interspecific hybridization between C. hongkongensis and C. angulata is completely successful in one direction. Furthermore, hybrids are viable, fast growing and completely fertile, which provides a promising method for the genetic improvement of oysters as a new aquaculture stock in southern China.     

Oocyte and embryo quality in Crassostrea gigas (Portuguese strain) during a spawning period in Algarve,South Portugal

Egg quality is one of the most important factors determining larval viability. The study of oocytes released by `wild' broodstock will contribute to the definition of quality criteria applied to hatcheries as well as being an indicator of the oyster reproduction potential and aquaculture ongrowing systems. The aim of this study was to determine the relationship between condition of Crassostrea gigas spp. angulata (Portuguese strain) from `wild' broodstock (condition index, gonadal maturity and number of oocyte released), oocyte biochemistry and hatching rate of eggs during the spring/summer of 1995. Stages of gonadal maturity and condition index indicated that natural spawning of this species occurred between April and August with the highest spawning intensity occurring in June. Analyses demonstrated that C. gigas oocyte organic matter consist of 44–74 % proteins, 16–38 % lipids and 7–12 % carbohydrates. A significant relationship was observed between some biochemical parameters – organic matter and lipid content – and broodstock condition index and hatching rate. It seems that these two oocyte parameters (organic matter and total lipids) could be used to define quality of oocyte and thus larval viability. The oocyte protein content was also found to be associated with broodstock and larval quality. In summary, these data are a contribution to the knowledge of the reproductive cycle of oysters in Europe and may be useful in improving hatchery management of this species.     

Effect of Rhodomonas salina addition to a standard hatchery diet during the early ontogeny of the scallop Pecten maximus

The main objective of this study was to identify algal diets that maximize the survival and growth and alter the biochemical content of Pecten maximus larvae with the aim of improving metamorphosis. We also evaluated the potential of the cryptophyceae Rhodomonas salina as a food source for these larvae. Two flagellates, Isochrysis aff. galbana (T) and Pavlova lutheri (P), and two diatoms, Chaetoceros gracilis (C) or Skeletonema costatum (S), were tested as two ternary diets, namely PTC and PTS. PTC and PTS were compared with diets that also included R. salina (R). The addition of R. salina and the replacement of C. gracilis by S. costatum in the traditional hatchery diet seem to be two interesting alternatives for increasing the productivity of larval scallop culture and improving the metamorphosis rate. With these two diets, larval growth increased and metamorphosis was observed to occur more rapidly. Moreover, our results showed that the addition of R. salina significantly improved the overall condition of the larvae by promoting an increase in organic matter and total lipids. This accumulation of lipids during ontogeny seems to promote larvae to grow and to complete metamorphosis more rapidly than with the other diets. The level of polyunsaturated fatty acids in the algae could also at least partially explain the results obtained, since the PUFA level of C. gracilis was about half those of S. costatum and R. salina.     

Effect of the culture system and culture technique on biochemical characteristics of Pavlova lutheri and its nutritional value for Crassostrea gigas larvae

Pavlova lutheri was cultivated in carboys using batch technique and in a flat alveolar photobioreactor (FAP), using initially batch and then semi‐continuous techniques. Growth and productivity of the cultures were compared and their nutritional quality was assessed by analysing their biochemical composition (gross composition, fatty acids and sterols) and by evaluating their food value for Pacific oyster (Crassostrea gigas) larvae as bispecific diet in association with Chaetoceros calcitrans forma pumilum. The highest productivity was achieved with the FAP operating in semi‐continuous mode. Gross composition of P. lutheri was similar in all cultures, while cellular organic matter content of the microalga grown in FAP in semi‐continuous mode was lower. Significant differences in fatty acid content were detected with respect to the n‐6 polyunsaturated fatty acid fraction, which was lower in cells cultivated in the FAP in semi‐continuous mode. As concerns the main individual fatty acids, docosahexaenoic acid (DHA) content was higher in cells cultivated in the photobioreactor in batch mode than in carboys. The neutral lipid fraction contained seven principal sterols and the comparison among the cultures evidenced different proportions and different patterns. No differences were observed among larvae fed diets containing P. lutheri grown in carboys or in the FAP.     

Effects of mono‐species and bi‐species microalgal diets on the growth,survival and metamorphosis of auricularia larvae of the California sea cucumber,Parastichopus californicus (Stimpson, 1857)

The effects of mono‐species and bi‐species microalgal diets on body length, survival and metamorphosis of auricularia larvae of the California sea cucumber, Parastichopus californicus, were tested in two separate laboratory feeding experiments. The first examined eight single species of microalgae – Chaetoceros calcitrans (Cc), Chaetoceros muelleri (Cm), Dunaliella tertiolecta (Dt), Isochrysis sp. (Tahitian strain: TISO) (Ti), Pavlova lutheri (Pl), Phaeodactylum tricornutum (Pt), Tetraselmis suecica (Ts) and Thallassiosira pseudonana (Tp). The second experiment took the five most effective single species from the first experiment (i.e. Cc, Cm, Dt, Pl and Ti) and presented them in all possible binary combinations. In the first experiment, Cc was determined to be the best diet on the basis of generating a significantly higher metamorphic rate (65.5 ± 4.2%, mean ± SD) than any other species and leading to one of the best survival rates (72.3 ± 7.6%) and greatest body lengths (831.6 ± 5.6 μm at day 14). In the second experiment, diets containing Cc generally produced the highest survival and metamorphic rates and greatest body lengths (except Cc/Cm) of all mixed diets, although no bi‐species treatment was ever significantly superior to a control of Cc alone. Of the various mono‐species and bi‐species diets evaluated for rearing auricularia larvae of P. californicus, Cc (either alone or mixed with other species) is recommended.     

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.     

Flavobacteria colonizing the early life stages of hatchery‐incubated Chinook salmon Oncorhynchus tshawytscha (Walbaum 1792) are markedly diverse

Flavobacterial diseases are significant impediments to hatchery‐based fishery conservation and aquaculture productivity worldwide. Recent studies revealed a multitude of novel flavobacteria within the reproductive fluids and unfertilized eggs of feral Chinook salmon Oncorhynchus tshawytscha broodstock, some of which were associated with systemic disease. Herein, embryonated eggs/fry from these broodstock were assayed for flavobacteria while in incubator stacks in three hatcheries over 2 years, as was the water entering hatchery incubators. Overall, >65% of sampled eggs and 38% of fry were colonized by flavobacteria. One hundred and ninety‐one egg and fry‐associated flavobacterial isolates were characterized phenotypically and via 16S rRNA gene sequencing and phylogenetic analyses, revealing that the majority fell into 22 clades (i.e., 15 Flavobacterium spp. groups and seven Chryseobacterium spp. groups) that varied in presence by facility. Although some matched previously described fish‐pathogenic species, the majority were distinct from all described flavobacteria and likely represent novel species. Of concern, iodophor disinfection at the commonly utilized dose/duration for egg‐surface disinfection did not eliminate flavobacteria. Results also implicated maternal routes of infection and source water for some flavobacteria. In total, study findings underscore the complexity of flavobacterial ecology within hatchery environments and highlight the need for improved hatchery biosecurity practices.     

Performance of Mixed Species and Mono‐specific Algal Diets for Culture of Larval Western School Prawns,Metapenaeus dalli

The effect of three mono‐specific and four combinations of the diatoms Chaetoceros muelleri, Chaetoceros calcitrans, and the chlorophyte Tetraselmis suecica on survival, development, and dry weight of the western school prawn, Metapenaeus dalli, was assessed from protozoea I until mysis I. The development and dry weight of larvae were significantly greater when fed diets comprising C. muelleri and/or T. suecica. A fourth diet, consisting of all three microalgal species also performed just as well. Survival alone was a poor measure of the performance of the various diets. Larvae fed with C. calcitrans, either alone or in a mixed diet with either C. muelleri or T. suecica, had significantly slower development and lower dry weight. Overall performance, assessed using the normalized biomass development index, determined that both mono‐specific and mixed diets containing C. muelleri and T. suecica were among the best for M. dalli larvae. These results for M. dalli are consistent with those found for commercially grown penaeid prawns. This study enhances the limited knowledge on the feeding requirements of metapenaeid prawn larvae. Moreover, the results will help improve hatchery methods for the aquaculture‐based enhancement of M. dalli in the Swan‐Canning Estuary and potentially increase the abundance of this iconic recreational species.     

Assessment of the performance of Pacific oyster (Crassostrea gigas) larvae fed with fresh and preserved Pavlova lutheri concentrates

The Prymnesiophycea Pavlova lutheriwas produced using a traditional technique (batch mode in carboys) and by an innovative technique (semi-continuous mode in alveolarphotobioreactor). Two experimental feedingtrials were carried out with Pacific oyster(Crassostrea gigas) larvae with freshand preserved (4 °C and 1 °C)P. lutheri concentrates used inmonospecific and bispecific diets, incombination with fresh Chaetoceroscalcitrans forma pumilum. Nodifferences in terms of gross composition andlarval performance were noticed between thefresh algae biomass produced by the twotechniques. The low temperatures allowedpreservation of the nutritionalcharacteristics of the P. lutheri freshculture for the time period considered (27days). The P. lutheri concentratespreserved at 4 °C or 1 °C didnot differ substantially in terms ofnutritional value. Larvae fed a monospecificdiet of P. lutheri, both fresh andpreserved, exhibited a modest growth rate (<2.1 µm day^–1), in some cases notsignificantly different from that observed inthe unfed larvae (the control), and a lowsurvival rate. In contrast, when Chaetoceros calcitrans forma pumilumwas used as a monospecific diet, good growthperformance (>4.5 µm day^–1) and ahigh survival rate (>86%) were observed inlarvae. A substitution of 50% (trial 1) or80% (trial 2) of fresh C. calcitransforma pumilum with the preserved P. lutheri concentrates did not adverselyaffect growth rate or survival of C.gigas larvae.     

Enhancement of reproductive performance in shrimp Litopenaeus vannamei (Boone, 1931) by supplementation of Ulva clathrata meal in maturation diet in two commercial hatcheries

The effect of supplementing dehydrated seaweed Ulva clathrata (20 g/kg) in the squid fraction of a formulated fresh diet on the reproductive performance of Litopenaeus vannamei broodstock was evaluated in two commercial hatcheries (A and B). The origin of broodstock, use of ablation on females, tank/culture conditions (for maturation, spawning, and larval rearing) were different between hatcheries. Daily mortality was higher (p < .01) for females in the control group compared to Ulva‐fed group of hatchery A, where females were ablated. No differences in mortality were found for unablated females in hatchery B, or with males from either hatchery. In hatchery A, broodstock fed Ulva produced more eggs (an increase in +5% compared to control, p < .05) and nauplii per female (+18%, p < .01). In hatchery B, broodstock fed Ulva produced significantly more eggs (+26%, p < .05) and nauplii per day (+33%, p < .05). In hatcheries A and B, eggs from broodstock fed Ulva had increased hatching rates (+13 and +7%, respectively, p < .001 in both cases). The number of spawns per day had a tendency to be higher in broodstock fed Ulva in both hatcheries, but the difference did not reach statistical significance (+14% for hatchery A and +20% for hatchery B). Dehydrated U. clathrata appears therefore as a functional additive in L. vannamei maturation diets that enhances the reproductive performance at commercial scale, regardless of the management conditions.     

Phenotypic indicators for cultured pearl size improvement in the black‐lipped pearl oyster (Pinctada margaritifera): towards selection for the recipient growth performance

The black‐lipped pearl oyster, Pinctada margaritifera, is the most important farmed species in French Polynesia and the basis of the most valuable export industry. Mass production of black pearls relies on a surgical operation requiring tissue from a donor pearl oyster to be grafted, together with a nucleus made of shell, into the gonad of a recipient oyster. Improving pearl size through family selection remains one of the main challenges for future aquaculture development. This study analyses the relative contribution of donor and recipient oysters to pearl size. To this end, hatchery‐produced donor oysters of two batches, large and small (based on shell height), were used to supply grafts for recipients, which were then monitored individually for their growth performance by recording shell height, width, and thickness, and total live weight (flesh + shells) every 6 months (four biometric measurement times) over 20 months of culture. Pearls issued from the two batches of donors showed no significant differences in nacre weight or thickness. In contrast, recipient oyster shell height and total weight were increasingly positively correlated with these pearl size parameters over the culture period, becoming significant at 8 months post‐grafting. Potential therefore exists to use shell height and oyster weight as phenotypic indicators for selective breeding of recipient oysters with high growth performance to increase pearl size in P. margaritifera.