Hatchery Culture Research Articles

Effects of ethylenediaminetetraacetic acid on growth and survival of long‐spined sea urchin Diadema antillarum larvae

AbstractObjectiveThe presence of heavy metals in seawater is a major challenge for hatchery culture of sea urchin larvae due to their sensitivity to metal pollution. The impact of heavy metals in seawater for sensitive marine larviculture could be minimized via chelation of metals using chemical compounds such as ethylenediaminetetraacetic acid (EDTA).MethodsIn this study the effects of EDTA were tested for the long‐spined sea urchin Diadema antillarum during larviculture at two concentrations (10 μM and 50 μM) and two exposure durations (6 and 24 days postfertilization). Growth and survival of larvae were evaluated as response variables.ResultSignificant differences in growth and survival of larvae were found among the treatments at different EDTA concentrations and exposure durations. The 10‐μM EDTA treatment enhanced growth and survival of larvae relative to control for both exposure durations. The 50‐μM EDTA treatment was unsuitable for long‐spined sea urchin larviculture due to reductions in growth and survival.ConclusionThe use of 10 μM EDTA during embryo incubation and larviculture is expected to improve long‐spined sea urchin larval fitness, leading to improved hatchery production.

Ammonia Stress Disturbs Moult Signaling in Juvenile Swimming Crab Portunus trituberculatus

Ammonia is a significant concern during hatchery culture in brachyuran species, and its accumulation may lead to abortive moulting and large-scale deaths of the early juveniles. To date, the underlying mechanism for ammonia-induced alteration of the moulting process is still unknown. In this study, we aimed to investigate the effects of ammonia on the moulting as well as the potential mechanisms in early juveniles of the swimming crab Portunus trituberculatus, an important aquaculture species in China. We evaluated the survival rate and moulting rate of the juvenile crabs (C2) and analyzed the expression pattern of the genes in key components of molt signaling during a complete moulting cycle under different concentrations of ammonia nitrogen (the control group: <0.1 mg/L; the LA group: 5 mg/L; and the HA group: 20 mg/L). The results showed that: (1) the survival rate in the LA and HA groups was lower than that in the control group at the end of the experiment, and moulting death syndrome (MDS) was only observed in the HA group; (2) the moulting rate was higher in the LA group and lower in the HA group compared to the control group; (3) consistent with the results of the moulting experiment, MIH showed decreased expression, and genes related to ecdysteroid synthesis, ecdysteroid receptors, and responsive effectors exhibited increased expression in the LA group compared to the control group; and (4) although MIH expression was upregulated, increased expression of the genes associated with ecdysteroid synthesis, ecdysteroid receptors and downstream effectors still observed in the HA group. Our results indicated that low levels of ammonia can promote moulting in juvenile swimming crabs by inhibiting the expression of MIH and activating moult signaling, whereas high levels of ammonia inhibit moulting and lead to MDS through impairing moult signaling.

Effects of volitional emigration timing and smolt size on survival and age-at-return in a Pacific salmon hatchery population

Many Pacific salmon populations are returning from sea at younger ages and smaller sizes. Hatchery culture, management practices, and environmental factors influence juvenile release size and emigration timing, which in turn affect important demographic characteristics in returning adults. We analyzed data from approximately 345,000 tagged spring Chinook Salmon juveniles exiting Cle Elum Supplementation and Research Facility (Yakima River, Washington, USA) acclimation sites over thirteen brood years (2002–2014), evaluating smolt size, emigration timing, river flow, juvenile survival, and age-at-return. We observed a relationship between size and volitional exit timing of smolts from acclimation sites, with larger fish tending to emigrate earlier than smaller fish. Early emigration was also coincident with lower river flows near acclimation sites. Later emigration timing was correlated with an increase in apparent survival of juveniles to Bonneville Dam (500–530 km downstream of acclimation sites), but also with a lower rate of survival to return from sea. In general, for juveniles successfully emigrating downstream of Bonneville Dam, age-at-return increased with decreasing juvenile fish size and later emigration timing. Our results support a growing body of evidence that hatchery practices may result in larger smolts that tend to return at younger ages. Given the biological and economic consequences of younger age-at-maturation, methods to reverse this trend should be further explored and implemented.

The embryonic and larval development of the long-lived, keystone mussel Modiolus modiolus: Implications for its restoration using conservation aquaculture

Biogenic reefs formed by bivalves are biodiversity hotspots globally endangered due to anthropogenic pressures. In Strangford Lough (Northern Ireland) bottom trawling caused extensive damage to reefs formed by the horse mussel Modiolus modiolus, compromising their conservation status. Full cycle aquaculture has been proposed as a potential restorative strategy whereby hatchery grown horse mussel juveniles can be used to reseed impacted beds, but this approach requires a thorough knowledge of the species biology. For M. modiolus, a long-lived, cold-water mussel, there is no clear consensus on the reproductive strategies and duration of the larval development cycle.This study presents the results of the first successful, full cycle aquaculture hatchery for M. modiolus in Atlantic Europe, from fertilized egg to spat. The use of air exposure was the only successful method to induce spawning in M. modiolus overcoming a known obstacle in the captive breeding of this species. Spawning lasted five to eight days until broodstock mussels were spent. The duration of the larval cycle from fertilized egg to the pediveliger stage was 34 days while juvenile mussels reached a maximum length of 5.5 mm after six months. All larval stages were recorded: trochophore (t0 + 24 h), D-larva (t0 + 36 h), early umbonated veliger (t0 + 20 days), late veliger (t0 + 32 days) and pediveliger with active foot (t0 + 36 days). Although settlement trials using inert substrates were unsuccessful, juvenile spat were recorded six months after fertilization when live adult M. modiolus were introduced in the rearing tanks. Growth was significantly faster when the larvae were fed with the microalga Chaetoceros calcitans, on its own or combined with Tetraselmis suecica.The results of these breeding trials demonstrated that hatchery culture of M. modiolus is possible, with up to 2 million D-larvae obtained just 24 h after successful spawning of hatchery-kept broodstock. High mortalities and poor settlement indicate that further trials need to be undertaken to streamline protocols if captive breeding is to be considered a viable restoration option for the species. In the interim, a combination of strict protection and brood stock supplementation from healthy beds is the recommended restoration strategy.

Effects of Diet on Larval Survival, Growth, and Development of the Sea Cucumber Holothuria leucospilota.

Because most tropical sea cucumbers have been overexploited around the world, the sea cucumber Holothuria leucospilota has become increasingly commercially important in recent years. Restocking and aquaculture of H. leucospilota using hatchery-produced seeds could both enhance declining wild populations and provide sufficient beche-de-mer product to satisfy increasing market demand. Identifying an appropriate diet is important for successful hatchery culture of the H. leucospilota. In this study, we trialed different ratios of microalgae Chaetoceros muelleri (2.00-2.50 × 106 cells/mL) and yeast (Saccharomyces cerevisiae, ~2.00 × 106 cells/mL) in diets for H. leucospilota larvae (6 d after fertilization, referred to as "day 0") at proportions 4 : 0, 3 : 1, 2 : 2, 1 : 3, and 0 : 4 by volume, in 5 treatments (A, B, C, D, and E, respectively). Larval survival rates in these treatments decreased over time, with the survival highest in treatment B (59.24 ± 2.49%) on day 15 (double that of the lowest rate in treatment E (28.47 ± 4.23%)). For any sampling event, larval body length in treatment A was always the lowest after day 3, and that for treatment B was always the highest, except on day 15. The maximum percentage of doliolaria larvae occurred in treatment B (23.33%) on day 15, followed by treatments C, D, and E (20.00%, 10.00%, and 6.67%, respectively). No doliolaria larvae occurred in treatment A, and pentactula larvae occurred only in treatment B (3.33%). On day 15 in all treatments, late auricularia larvae had hyaline spheres, but these were not prominent in treatment A. Densities of juveniles attaching to settlement plates varied with treatments, and the values were very low for the larvae only fed microalgae (A, 2.39 ± 1.95 ind per plate) or yeast (E, 2.13 ± 1.05 ind per plate)-only ~5% of the maximum number settling in treatment B (45.56 ± 7.24 ind per plate). Increased larval growth, survival and development, and juvenile attachment indicates that diets combining microalgae and yeast are more nutritionally balanced than single diets for hatchery of H. leucospilota. A combined diet of C. muelleri and S. cerevisiae at a 3 : 1 ratio is optimum for the larvae. Based on our results, we propose a larval rearing protocol to facilitate mass production of H. leucospilota.

Thermotolerance of Greenshell™ mussel spat (Perna canaliculus) improved by prickly pear (Opuntia ficus indica) treatments

Cultured Greenshell™ mussels (Perna canaliculus) are exposed to biotic and abiotic stresses, all of which can negatively impact growth, fecundity, and survival. These impacts are especially pronounced in sensitive larval and spat stages and may result in substantial losses when spat are transferred from hatchery to grow-out farms. Immersion in solutions of plant extracts have been shown to improve stress tolerance in certain aquatic species and may offer new husbandry and market access opportunities, e.g., more amenable to organic farming practices. Here the efficacy of immersing P. canaliculus spat in ‘high’ or ‘low’ concentrations of prickly pear cactus (Opuntia ficus indica) solutions was examined. Solutions were made from either dry cactus leaf powder i.e., 4.5 (low) or 45 (high) g L−1 or cactus fruit extract (4 μl or 40 μl L−1) and mussels immersed for 1 h to stimulate potential defence mechanisms within mussels prior to acute thermal challenge.Following a subsequent 1 h thermal shock, the predicted 50% survival temperature (LT50) was raised following pre-treatment with O. ficus indica solutions. However, higher resilience to thermal stress was evident in P. canaliculus spat immersed in low concentration solutions of O. ficus indica powder (LT50 = 32.3 °C) and extracts (LT50 = 32.4 °C) compared to spat in immersed in higher concentrations (i.e., LT50 = 31.8 °C ‘Powder’ and 31.4 °C ‘Extract’ respectively) and to naïve controls (LT50 = 30.7 °C). The results provide evidence for the potential for bioactive plant extracts to augment physiological resilience in a shellfish species. While internal biochemical validation is required, the straightforward exposure protocols applied here would be readily transferrable into commercial hatchery culture methods for P. canaliculus.

Improving the environment for kelp hatchery culture in tanks with bottom aeration using a skeleton collector

Hydrodynamic and light conditions may be affected by the frame system that carries the string (collector) used to produce kelp seedling strings in kelp hatcheries. However, no studies have analysed the effect of the collector type on these key environmental factors to assess hatchery suitability. In this study, two experimental set-ups were designed to evaluate the hydrodynamic environment and light availability using two distinctive collectors that have been used for kelp hatchery cultures in tanks with bottom aeration. A standard collector of walled PVC pipe was compared with an alternative collector consisting of a steel skeleton with a fully open frame structure. The results show that the two types of collectors produced different environmental effects. The skeleton collector displayed a significantly lower reduction in the water velocity compared with the pipe collector, and therefore, its design favours water circulation and exchange through the system to a greater extent. This effect was more significant as the aeration level increased. The skeleton collector also provided better light availability, with a significance that depended on the illumination source positions at different faces of the collector. The differences were greater on the inside faces and with illumination from the sides of the collector. The findings are discussed based on prior experience and the literature on kelp hatchery practices.

The role of hatcheries in the decline of Lake Ontario Atlantic salmon

Lake Ontario Atlantic salmon (Salmo salar) were one of the first species of fish to be cultured in Canada. Their story goes from abundance in the 1700s to protective legislation in 1807, then hatchery culture in 1866 and finally ends in extirpation in 1898. The standard narrative is that Samuel Wilmot’s hatchery efforts briefly staved off their loss from the Lake Ontario basin. However, that story is replete with inaccurate assumptions, unfounded faith in technological solutions, and a belief that numbers of fish released was an accurate measure of success. We challenge the narrative around the perceived benefits of these hatchery efforts and suggest instead that they contributed to the decline of Atlantic salmon in Lake Ontario through the mining of wild gametes, transferring eggs out of basin, mixing locally adapted populations across streams, and the negative genetic effects of releasing hatchery fish.

Ontogenetic variation in digestive enzyme activities within embryos and newly-hatched larvae of the tropical spiny lobster, Panulirus ornatus

While there is considerable interest in aquaculture of spiny lobsters (Palinuridae), limited knowledge of nutritional requirements during early life stages remains a major impediment to successful hatchery culture. To better determine endogenous nutrient utilisation during the early life stages of the tropical spiny lobster, Panulirus ornatus, we examined ontogenetic variation in digestive enzyme activities within developing embryos and newly-hatched phyllosoma in the absence of an exogenous food source. Specifically, α-amylase, non-specific esterase, and trypsin-like protease activities were quantified to indicate the relative importance of macronutrients (i.e., carbohydrate, lipid, and protein) and gauge the digestive potential of newly-hatched phyllosoma during transition from endogenous to exogenous nutrient sources. Ontogenetic variation in digestive enzyme activities indicated that lipid, protein, and carbohydrate were sequentially utilised by embryos. Early increase in non-specific esterase activity suggests that lipid is the most critical macronutrient for early embryonic development, with protein and carbohydrate becoming increasingly utilised shortly before and after hatching. The observed peak in trypsin-like protease activity during the first day post-hatch presumably allows phyllosoma to make best use of dietary items that are high in protein at first-feeding. In the absence of an exogenous food source after hatching, changes in digestive enzyme activities suggest that a metabolic shift from protein to lipid occurred, coinciding with the timing of the ‘point-of-no-return’ for Stage I phyllosoma of P. ornatus. Our results highlight the importance of providing an exogenous protein-rich food source to phyllosoma soon after hatch and provide a foundation for further study into broodstock nutrition and egg quality of this species.

Dynamic Immune Response to Vibriosis in Pacific Oyster Crassostrea gigas Larvae during the Infection Process as Supported by Accurate Positioning of GFP-Tagged Vibrio Strains.

As the immune system is not fully developed during the larval stage, hatchery culture of bivalve larvae is characterized by frequent mass mortality caused by bacterial pathogens, especially Vibrio spp. However, the knowledge is limited to the pathogenesis of vibriosis in oyster larvae, while the immune response to pathogenic microorganisms in this early life stage is still far from being fully elucidated. In this study, we combined green fluorescent protein (GFP)-tagging, histological and transcriptomic analyses to clarify the pathogenesis of experimental vibriosis and the mechanisms used by the host Pacific oyster Crassostrea gigas larvae to resist infection. The Vibrio strains first colonized the digestive system and rapidly proliferated, while only the transcription level of IκB kinase (IKK) and nuclear factor κB (NF-κB) associated with signaling transduction were up-regulated in oyster at 18 h post challenge (hpc). The mRNA levels for integrin β-1, peroxinectin, and heat shock protein 70 (HSP70), which are associated with phagocytosis, cell adhesion, and cytoprotection, were not upregulated until 30 hpc when the necrosis already happened in the larval digestive system. This suggested that the immunity in the early stages of C. gigas is not strong enough to prevent vibriosis and future research may focus on the strengthening of the gastrointestinal immune ability to defend vibriosis in bivalve larvae.

First data on aquaculture of the Tripletail, Lobotes surinamensis, a promising candidate species for U.S. marine aquaculture

AbstractThe Tripletail, Lobotes surinamensis, is a warm‐water pelagic fish that is increasingly targeted by U.S. anglers. The superior quality of Tripletail flesh coupled with the lack of domestic commercial fisheries stimulated interests to develop aquaculture of this species. In this work, photo‐thermal conditioning of captive‐held broodstocks promoted maturation in females, but spontaneous spawning was not observed. GnRHa slow‐release implants induced ovulation in late vitellogenic females but fertility remained below 10% when GnRHa was administered alone. However, spawns with high fertility (up to 85%) were obtained when a dopamine antagonist was administered in conjunction with GnRHa implants indicating dopamine inhibition impaired final gamete maturation, in particular sperm production in males, in aquaculture conditions. Tripletail larvae successfully initiated exogenous feeding on enriched rotifers followed by Artemia nauplii and were weaned to prepared feeds at 25 days post hatch, yet with low survival through the late phases of larval culture. Pilot grow‐out trials at low density in recirculating systems revealed impressive growth rates averaging over 170 g/month through a market size above 1 kg. While protocols for hatchery culture and grow‐out still need to be optimized, current data suggest that Tripletail could become a successful species for U.S. marine aquaculture.

A Novel RNA Virus, Macrobrachium rosenbergii Golda Virus (MrGV), Linked to Mass Mortalities of the Larval Giant Freshwater Prawn in Bangladesh.

Mass mortalities of the larval stage of the giant freshwater prawn, Macrobrachium rosenbergii, have been occurring in Bangladesh since 2011. Mortalities can reach 100% and have resulted in an 80% decline in the number of hatcheries actively producing M. rosenbergii. To investigate a causative agent for the mortalities, a disease challenge was carried out using infected material from a hatchery experiencing mortalities. Moribund larvae from the challenge were prepared for metatranscriptomic sequencing. De novo virus assembly revealed a 29 kb single-stranded positive-sense RNA virus with similarities in key protein motif sequences to yellow head virus (YHV), an RNA virus that causes mass mortalities in marine shrimp aquaculture, and other viruses in the Nidovirales order. Primers were designed against the novel virus and used to screen cDNA from larvae sampled from hatcheries in the South of Bangladesh from two consecutive years. Larvae from all hatcheries screened from both years were positive by PCR for the novel virus, including larvae from a hatchery that at the point of sampling appeared healthy, but later experienced mortalities. These screens suggest that the virus is widespread in M. rosenbergii hatchery culture in southern Bangladesh, and that early detection of the virus can be achieved by PCR. The hypothesised protein motifs of Macrobrachium rosenbergii golda virus (MrGV) suggest that it is likely to be a new species within the Nidovirales order. Biosecurity measures should be taken in order to mitigate global spread through the movement of post-larvae within and between countries, which has previously been linked to other virus outbreaks in crustacean aquaculture.

Biodegradable chelating agent improves the survival of early larvae for shellfish aquaculture

The toxicity of heavy metals commonly impacts the survival of crustacean and bivalve larvae in hatchery culture, and this has led to the widespread use of EDTA to decrease this toxicity. Since EDTA has a very poor biodegradability leading to potential persistent environmental effects, alternative methods to prevent heavy metal toxicity to shellfish larvae are needed. EDDS is a biodegradable potential alternative to EDTA for this application and was tested as a treatment of the seawater used for rearing aquaculture Greenshell™ mussel (Perna canaliculus) larval embryos in this study. Mussel embryos reared with EDTA or EDDS had significantly better survival than without. The concentrations and spatial distributions of heavy metals in D-veliger larvae as determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and X-ray Fluorescence Microscopy (XFM) suggested that chelating agents increased the levels of calcium in larvae while they reduced the concentration of zinc. In addition, where decreased accumulation of the other heavy metals was not observed, chelating agents affected their distribution within the larvae, especially for copper and arsenic. This is the first study to test the use of EDDS for aquaculture hatchery application and shows that EDDS is an effective biodegradable alternative to EDTA that can mitigate the effects of heavy metals for shellfish larval rearing.

Hatchery culture of European clam species (family Veneridae)

Aquaculture and capture production of clam species have great economic value in Europe. The production is dominated by the introduced species, Manila clam, Ruditapes philippinarum, which has displaced some of the native species of clams. In Europe, landings of autochthonous clams have decreased in the recent years due to overfishing, failure in recruitment, abiotic stress and diseases. Due to aforementioned factors, seed production in hatcheries has become essential to ensure the sustainability of the fisheries and aquaculture production of European native clams. Many studies have focused on the different steps involved in hatchery rearing, but the volume of seed of native species produced in commercial hatcheries is still relatively low in comparison to the exotic Manila clam. Presently, in European hatcheries, seeds from only two native species, Ruditapes decussatus and Venerupis corrugata, are produced at industrial scale. The present review analyses the state of hatchery culture of European native clam species, and the aims are to transfer information to the industry and identify critical gaps that might be impeding the development of hatchery production.

Use of Bacteriophages to Control Vibrio Contamination of Microalgae Used as a Food Source for Oyster Larvae During Hatchery Culture.

Cultured microalgae are the primary food source for oyster larvae during hatchery culture and are a potential vector for Vibrio spp. infection of larval cultures. Bacteriophages have shown potential for controlling contamination of Vibrio spp. in aquaculture systems and their application could be an effective biological control method to eliminate such bacterial contamination of microalgae. This study investigated whether Vibrio-free microalgae sources could be ensured via the application of Vibrio specific phages. As a first step, four different Vibrio bacteriophages (belonging to the Myoviridae viral family) were isolated from marine waters in Queensland, Australia and used in challenge tests against a Vibrio host species, previously isolated from New South Wales oyster hatchery and found to be closely related to V. alginolyticus (ATCC 17749). The genome sequence of one of the four isolated bacteriophages, Vibrio Φ-2, that displayed strongest virulence against the host was determined. The 242446bp genome of this bacteriophage was predicted to encode 217 proteins with an average GC content of 43.91%, containing putative thymidine kinases and a lysin enzyme. Application of these bacteriophages to pathogenic Vibrio spp. contaminating microalgae suspensions resulted in significant decreases in their numbers within 2h. Findings indicated that direct application of bacteriophages to microalgae suspensions could be an effective method of reducing the occurrence of vibriosis in oyster hatcheries.

Estimating predation rates of restocked individuals: The influence of timingof-release on metapenaeid (shrimp) survival.

Post-release mortality is one of the greatest obstacles in many aquaculture based enhancement programs [1-4], and often the downfall of stock enhancement efforts, regardless of great successes in hatchery culture. Predation is widely known to be a major factor in post-release mortality in hatchery-raised juveniles [5,6] accounting for up to 95 % of post-release mortality [7], and can quickly turn stock enhancement into an expensive exercise in making food for predatory species [8].

Maintaining a wild phenotype in a conservation hatchery program for Chinook salmon: The effect of managed breeding on early male maturation.

In many salmonid species, age and size at maturation is plastic and influenced by the interaction between genetic and environmental factors. Hatchery reared salmon often mature at an earlier age and smaller size than wild fish. Modern salmon conservation efforts have focused on managing the level of gene flow between hatchery and natural origin fish to minimize potential genotypic and phenotypic change. In salmonids, maturation probability is dependent on exceeding a genetically set threshold in growth rate and energetic status (and by association, body size) referred to as the probabalisitic maturation reaction norm (PMRN). Over fourteen years, we monitored the frequency of age-2 precocious male maturation (common term: age-2 minijack rate) and the PMRN of natural founder (FNDR), integrated natural-hatchery (INT), and segregated hatchery (SEG) broodlines of spring Chinook salmon, Oncorhynchus tshawytscha. The average age-2 minijack rate (± SEM) of the FNDR, INT and SEG broodlines was 48.2 ± 5.2%, 41.9 ± 3.6% and 30.9 ± 4.7%, respectively. Additionally, the PMRN WP50 (predicted weight at 50% maturation) of the SEG broodline was significantly greater (20.5 g) than that of the FNDR/INT broodlines (18.2 g). We also conducted a common garden experiment exploring the effects of less than one [INT (0–1)], one [SEG (1)] or two [SEG (2)] generations of hatchery culture on the age-2 minijack rate and PMRN WP50. Growth was not significantly different among broodlines, but age-2 minijack rates were significantly lower following two consecutive generations of hatchery culture: [INT (0–1): 68.3 ± 1.7%], [SEG (1): 70.3 ± 1.8%] and [SEG (2): 58.6 ± 0.4%] and the PMRN WP50 was significantly higher by 6.1 g after two generations of SEG culture. These results indicate that managed gene flow reduces phenotypic divergence, but may serve to maintain potentially undesirably high age-2 minijack rates in salmon conservation hatchery programs.

EFFECT OF FEED RAW MATERIALS TYPES ON DISSOLVED PROTEIN CONTENT, PROTEIN HYDROLYSIS LEVEL AND FEED NUTRITION CONTENT OF ORANGE MANGROVE CRAB (Scylla olivacea) LARVAE FEED

Feed is one of the factors that affect the success of hatchery culture of mud crab (Scylla olivacea). The use of artificial feed in the form of microdiet can ensure availability, lower production costs and higher flexibility than natural feed. During this time the artificial feed used is a commercial feed, which is relatively expensive, therefore the need for research to produce artificial feed of good quality, with a cheap price.. The objective of this research is to determine the combination of raw material of artificial feed protein which produce dissolved protein content, protein hydrolysis degree and best protein content of feed. The experimental design used was completely randomized with eight treatments and three replications. The treatments were the use of various combinations of feed protein ingredients : A) 100% Artemia flour, B) 100% fish meal, C) 100% squid meal, D) 50% Artemia and 50% fish meals, E) 50% Artemia and 50% squid meals, F) 50% fish and 50% squid meals, G) 35% fish, 35% squid and 30% Artemia meals, H) commercial feed. The parameters used were dissolved protein content, protein hydrolysis degree and protein feed content. The results showed that the difference of feed protein raw materials had significant effect (p &lt;0,05) on soluble protein content and feed protein hydrolysis degree. The highest content of soluble protein in in the diet with a protein raw material was squid meal, but not significantly different (P&gt; 0,05) than Artemia meal and combination between 50% Artemia and 50% squid meals, but significantly different (P &lt; 0.05) than other treatments. The highest degree of protein hydrolysis in the diet with a protein raw materials was Artemia meal, but not significantly different (P&gt; 0.05) than in commercial feed as well as combination between Artemia and squid meal (P&gt; 0.05), but significantly different (P &lt;0, 05) compared to other treatments. Feed protein content according to the needs of mangrove crab larvae. Fat content with a protein raw materials was 100% artemia meal was higher than the need. Carbohydrate content with a protein raw materials were 100% artemia meal, a combination of 50% artemia meal and 50% squid meal and commercial feed according to the needs of mud crab larvae.

Larval and early juvenile culture of two giant clam (Tridacninae) hybrids

The capacity for inter-specific hybridisation to yield improvements in animal production has long been realised in the aquaculture sector. However, the extension of hybridisation to improve production of giant clams (Tridacninae) has received little research attention. Aquaculture production of giant clams is directed primarily at aquarium markets, and hybridisation offers an opportunity to diversify available products. Here we report on the successful inter-specific hybridisation of Tridacna maxima and T. noae, and assess hybrid performance during hatchery culture. Both maternal and paternal hybrid crosses of T. maxima/T. noae yielded competent larvae. Fertilisation success was significantly lower (40.7 ± 3.2%) for the T. maxima♀/T. noae♂ cross compared to the T. noae ♀/T. maxima♂ cross (89.3 ± 1.8%; χ2 = 154.03, P < 0.01). Despite the disproportionate fertilisation success, the two hybrids had similar survival curves (survival = 2.03 × days-2.08, r2 = 0.67, P = 0.13) for the first 30 days of culture. Antero-posterior shell growth (APM) was superior in the T. maxima♀/T. noae♂ hybrid (APM = 10(2.158+0.019×days)) when compared to the T. noae♀/T. maxima♂ hybrid (APM = 10(2.169+0.016×days)) over the same time frame (r2 = 0.92, P < 0.001). Both survival and growth of the hybrids exceeded that reported in the literature for pure-strain hatchery culture of giant clam species. This suggests capacity for hybridisation to contribute to giant clam aquaculture production. The application of hybridisation to supply aquarium markets and necessary considerations for manipulating stock genetics are discussed in view of these results.

Artificial reproduction of Holothuria polii: A new candidate for aquaculture

Holothuria polii (Delle Chiaje, 1823) is a common Mediterranean sea cucumber and has recently become a highly exploited target species destined mainly to the Asian markets. Unregulated harvesting is putting the natural stocks at risk, with potential consequences for the benthic communities to which these organisms belong. In response aquaculture, sea ranching and restocking could become solutions to this issue in the Mediterranean region. In this study, we present the first results on artificial breeding of H. polii, describing the spawning induction, larval development and early juvenile growth in hatchery cultures, our goal is to develop a rearing protocol for this species. The trials were conducted between July and September 2016. Holothuria polii was induced to spawn by testing two different methods. The thermal shock proved a simple and effective method for obtaining healthy gametes from this species. Larval development in H. polii progressed through five stages, reaching the pentactula stage in 10 days. Three different microalgal feeding regimens were tested for larval breeding; the higher feeding concentration 20,000–40,000 cells mL−1 proved to be the best, with 14% of the larvae metamorphosed into settled juveniles by adhering to the artificial substrates at 15 days. Our results indicate that H. polii performs very well in the hatchery rearing during the larval and juvenile phases; this indicates that this species could be a valuable new candidate for aquaculture in the Mediterranean region both for production and for restocking purposes.