Candidate For Aquaculture Research Articles

Assessment of a Novel Stress and Immune Gene Panel on the Development of Australasian Snapper (Chrysophrys auratus) Larvae

Background: Larvae development is a critical step in aquaculture, yet the development of immune and stress responses during this early phase of life is not well understood. Snapper is a species that has been selected as a candidate for aquaculture in New Zealand. Methods: In this study we explore a set of 18 genes identified as potentially being involved in the stress and immune responses of snapper larvae during the first 30 days of development. Larvae were collected between 11:45 a.m. and 16:10 p.m. each day. Results: Most genes did not deviate from baseline expression throughout the 30 days, with some exceptions between Days 0 and 6 with glyceraldehyde-3-phosphate dehydrogenase and superoxide dismutase, mitochondrial uncoupling protein 2-like, peroxiredoxin-5 mitochondrial, and hepcidin, which predominantly increased and then stabilized by Day 6 until Day 30. Some genes were affected by the time of day, such as actin cytoplasmic 1 and catalase isoform X2. Conclusions: This exploratory study is the first to look at a panel of stress- and immune-related marker gene expression during early snapper development. It sets methods in place to explore the expression of these markers and determine the impact of different potential stressors, such as alternative food sources and other environmental changes. It also highlights the importance of same time of day collections for gene expression studies.

What temperature is best for the offshore farming of the Australasian snapper, Chrysophrys auratus? A collective examination of growth, FCR, O2 consumption and welfare

ABSTRACT The Australasian snapper (Chrysophrys auratus) is a candidate for offshore aquaculture in New Zealand. The culture of snapper requires knowledge of the best locations for farms and a key variable is water temperature. The oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis suggests fish performance is optimised at the temperature that maximises absolute aerobic scope (AAS), whereas the ‘multiple performances–multiple optima’ (MPMO) idea, suggests AAS and other performance measures can have different optimal temperatures. Therefore, the applicability of the OCLTT for snapper was tested by holding juveniles at 15, 18, 21, or 24°C for two months and constructing thermal performance curves (TPCs) for specific growth rate (SGR), feed conversion ratio (FCR) and AAS, and an assessment of welfare indicators. We hypothesised that the OCLTT would apply with all TPCs optimised at 21°C. However, AAS showed no discernible peak with temperature (although lower at 15 than 18°C); SGR and FCR improved non-linearly with temperature; and welfare indicators varied little with temperature. This lack of aerobic limitation and evidence of MPMO suggests snapper are amenable to culture across a significant temperature range with warmer water likely providing the highest levels of productivity with maintained welfare.

Embryonic and larval development of black jewfish, Protonibea diacanthus: A new candidate for aquaculture in northern Australia

Black jewfish Protonibea diacanthus is a large, commercially important fish distributed across the tropical Indo-Pacific. In Australia, there is an established commercial wild fishery for the species but it’s aquaculture potential has not been investigated. This research presents hatchery production of native P. diacanthus in Darwin, Australia and documents ontogeny of early life stages of this species over three trial runs. Wild P. diacanthus were induced to spawn with luteinizing hormone-releasing hormone analog (LHRHa) and eggs were released approximately 25–28 h after injection (0.88 ± 0.01 mm in diameter with oil globule 0.24 ± 0.01 mm). Larvae hatched 12 h after spawning. At one day post hatch (dph) larvae were 2.68 ± 0.01 mm standard length with 0.15 ± 0.01 mm oil globule diameter. Larvae mouths opened at 31 h post hatch (hph) and first feeding was seen at 57 hph. Swim bladder inflation (92 %) occurred between 40 and 62 hph. Larvae were progressively fed rotifers, Artemia and Otohime microdiet, and metamorphosis occurred between 20 and 25 dph, completing as they reached over 13 mm standard length. Tail biting cannibalism began with the onset of metamorphosis and caused significant mortality until approximately 24 dph when metamorphosed juveniles could be handled and moved to low stocking density systems. This study demonstrates that northern Australian P. diacanthus is amenable to hatchery production and provides important foundational knowledge for this emerging aquaculture species.

Identification of two effective sex-specific DNA markers in silver arowana (Osteoglossum bicirrhosum)

The silver arowana (Osteoglossum bicirrhosum), often referred to as a living fossil, presents significant challenges in sex identification based on morphological characteristics, with its sex determination mechanism remaining poorly understood. This issue poses considerable obstacles to its captive breeding efforts. Given the species' substantial value for both consumption and ornamental purposes, it is a critical candidate for aquaculture. Through genome sequencing, read mapping, and alignment analysis of five male and five female silver arowanas, along with one mixed pool of males, we successfully identified two sex-specific SNPs and confirmed a ZW model of sex determination in this ancient species. These two SNPs demonstrated remarkable accuracy, achieving 100 % success in genetic sex identification, as validated by Sanger sequencing of PCR products from 135 individuals. Both sex-specific SNPs are located approximately 26 kb upstream of the foxl2 gene, indicating a potentially pivotal role for the foxl2 gene in the sex-determination process of the silver arowana. Consequently, we have developed precise molecular markers for sex identification in the silver arowana, significantly enhancing reproductive efficiency and promoting further industrial development. This achievement lays a foundational basis for investigating the sex-determination mechanism of the silver arowana and other osteoglossid fish, thereby advancing aquaculture practices within this species.

THE FOOD AND FEEDING HABITS OF AUCHEONOGLANIS OCCIDENTALIS (VALENCIENNES, 1840) INHABITING SEBORE RESERVOIR, MAYO - BELWA, ADAMAWA STATE

Sebore Reservoir is blessed with many commercial and potential aquaculture species but there is paucity of published information on their food and feeding habits especially Aucheonoglanis occidentalis. This study aimed at providing information on the food and feeding habits of A. occidentalis found in the reservoir. A total of 144 samples of A. occidentalis, were collected monthly for a period of one year. Fishing was done using gill nets and canoe. The fish specimens were washed with clean water and preserved in ice crest to minimize any post-mortem changes. The stomach contents of each of the A. occidentalis sample were identified and analysis was done using the numerical and frequency of occurrence methods. The results recorded from the 144 samples of A. occidentalis elucidated that 84 samples of A. occidentalis representing 58.33% have their stomach full with food, 51 (35.42%) were having a half-filled stomach and 9 (6.25%) were having an empty stomach. The higher number of A. occidentalis samples recorded with full stomach than the A. occidentalis samples with half - filled and empty stomach in the study area indicated that there was constant availability of food for the fish. Findings from this study indicated that the A. occidentalis from Sebore reservoir of Adamawa State is an Omnivore, which fed on both plant and animal materials, though it feeds mostly on animal materials (Insect parts, fish parts and unidentified worms) than on plants. The different varieties of food items observed in the gut make it a potential candidate for aquaculture.

Changes in the physiology and chitin metabolism in cultured juvenile Panulirus ornatus across the moult cycle

Crustaceans undergo periodic moulting events to facilitate growth, this is a physiological and energetically demanding process. In an aquaculture environment, crustaceans are generally cultured in a defined space and often at high densities, where exposure to cannibalism may be greater than in the wild. Panulirus ornatus is one such emerging aquaculture candidates, moulting frequently as juveniles and providing the opportunity to investigate the relationship between physiology and genetics throughout this important developmental period. In this study, P. ornatus juveniles were assessed every three days across the seventh to eighth juvenile moult phase, sampling was divided into six distinct time points. Brix index, hepatosomatic index, and circulating ecdysone concentrations were measured across these time points. The Brix index was validated as a useful tool for assessing the moult-stages of juvenile P. ornatus, with an increase in Brix value seen in the lead up to ecdysis. Chitin metabolism was mapped, with Chitinase 3 demonstrating hepatopancreas specificity, indicating a role outside of breakdown of dietary chitin. The investigation of physiological parameters across a moult cycle provides a basis for improving moult cycle staging in cultured P. ornatus juveniles and provides further characterisation of the changes that occur during moulting in this species.

Adaptability and nutritional analysis of a newly isolated Chlorella sp. NeZha in brackish and marine environments with potential bioeconomic impacts.

The microalga Chlorella sp. NeZha, recently isolated from a balcony environment, shows significant adaptability across various salinity conditions, including seawater (SeaW), freshwater (FreshW), and high salinity levels (45‰). This study investigates its potential for sustainable aquaculture and biotechnological applications. Morphological and genetic identification were conducted using optical microscopy and DNA sequencing. The microalga was cultivated in a 400 L outdoor photobioreactor, and its biochemical composition, including chlorophyll a, carbohydrate, protein, and lipid content, was analyzed. Its compatibility with zooplankton and growth in aquaculture wastewater were also evaluated. Chlorella sp. NeZha produced chlorophyll a at concentrations exceeding seaweed and Spirulina by 10- and 5-fold, respectively, with a dry weight chlorophyll a content of 34.25 mg/g and 25 pg./cell. The microalga also contained carbohydrate (~33%), protein (~20%), and lipids (~14%). It was compatible with zooplankton species, such as rotifers and brine shrimp, and showed promising growth in aquaculture wastewater. The findings suggest that Chlorella sp. NeZha is a viable candidate for sustainable aquaculture and biotechnological applications, offering high nutritional value and environmental resilience. Its adaptability to diverse salinity conditions and ability to thrive in wastewater highlight its potential for bioremediation and use as feedstock for zooplankton. Further research is recommended to optimize its cultivation and explore broader applications.

Effect of temperature on growth, expression of growth regulating genes, and deformity development of juvenile European plaice (Pleuronectes platessa)

The flatfish European plaice is a demersal, temperate species and a candidate for marine aquaculture. To better understand growth and the mechanisms involved in growth regulation, juvenile plaice (initial mean weight ± SEM, 10.4 ± 0.1 g) were reared in triplicate rearing tanks at three different temperature: ambient (average of 8.6 °C), 12 °C and 16 °C, for 100 days. Interactions between growth, expression of growth regulating genes, and skeletal development were studied to determine optimal rearing conditions for juvenile plaice. Juvenile plaice grew fastest at 16 °C, followed by the 12 °C group. The condition factor was inversely correlated to increased temperatures and was highest in the 8.6 °C group. At the start of the experiment, 11% of the fish had vertebra deformities. Increasing temperature resulted in higher frequency and severity of malformations, and the 8.6 °C group had 8% less vertebra deformities at the end of the experiment compared to other two groups. The 12 °C and 16 °C groups had similar frequency of deformed fish, however, the 16 °C had more severe deformities, measured as number of deformed vertebrae per fish. Temperature affected gene transcript levels of ghr, igf-1, and igf-1r in muscle and liver tissue differently. Hepatic igf-1 transcript levels increased with increased growth and temperature. Muscular igf-1r transcript levels increased with increasing temperature in each sampling, indicating that igf-1r corresponded with muscular growth. Based on the present findings, a rearing temperature of 12 °C is recommended for on-growing of juvenile plaice.

Intrapopulation variation in reproduction of Lessonia variegata J. Agardh

ABSTRACT Lessonia variegata is an Aotearoa-New Zealand (A-NZ)-endemic kelp with significant commercial potential. Overseas, Lessonia spp. are harvested for use as human and animal food, cosmetics, and bioactives for biomedical applications. In A-NZ, interest in developing cultivation methodologies and commercial applications for L. variegata is growing, especially because it is an exposed-shore species which makes it an ideal candidate for exposed-coast or open-ocean aquaculture. However, establishing cultivation of L. variegata in A-NZ is currently challenging because essential knowledge about its reproduction and sporophyte development is generally unknown. This preliminary study investigated the intrapopulation variation in the reproductive output of L. variegata individuals collected from one population on the north-east coast of the South Island, A-NZ by quantifying the number of spores released, the percentage and number of spores settling, their germination, sex ratio, sporophyte production and growth. There were significant differences among individuals in the number of spores released and germinated, as well as the production of sporophytes and their growth. However, the sex ratio and the percentages and numbers of spores settling were similar among individuals. Evident differences reported in spores released and development can have possible implications for aquaculture including biobanks or sporophytes production.

Dietary Pediastrum boryanum microalgal extract improves growth, enhances immunity, and regulates immune-related genes in Nile tilapia

BackgroundIdentifying alternative sustainable feed sources with high nutritional values is crucial for the future of environmentally and socially responsible aquaculture. In this regard, microalgae have been proven to have positive effects on fish health, which overwhelmed our interest in this study.MethodsPediastrum boryanum (P. boryanum) was incorporated into Nile tilapia feed at concentrations of 0, 0.75, and 1.5 mg/kg, as control, PbExt0.75, and PbExt1.5 groups to assess its effects on growth and biochemical indices, oxidant/antioxidant activities, immune and stress-related gene expression, and intestinal morphology.ResultsAfter 8 weeks, fish fed P. boryanum supplemented feed exhibited significant increases in final weight, length, condition factor, body weight gain, and specific growth rate, while the spleen-somatic index (SSI) and hepatosomatic index (HSI) showed no significant differences compared to the control group. Dietary P. boryanum supplementation also enhanced IgM levels and lysozyme activity, along with no marked effect on markers of liver function enzymes (alanine aminotransferase/ALT and aspartate aminotransferase/AST) or protein status (total protein and albumin). Furthermore, P. boryanum addition increased the activity of superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) enzymes, highlighting its antioxidant potential, whereas malondialdehyde (MDA) concentrations showed no significant differences among the groups. Gene expression analysis revealed that tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), and transforming growth factor-β1 (TGF-β1) expression notably increased in groups fed P. boryanum containing feed, while no significant difference was observed in hepatic Heat Shock Protein 70 (HSP70) mRNA expression. Histopathological examination revealed no adverse effects of P. boryanum supplementation on the liver, spleen, or intestinal tissues. Villous height and villous surface area were notably increased in the high P. boryanum supplementation group, suggesting improved intestinal integrity and nutrient absorption.ConclusionDietary P. boryanum supplementation can potentially improve growth performance, immune response, antioxidant status, and intestinal health of Nile tilapia, making it a promising candidate for sustainable aquaculture.

Melodious tuning of microbial dynamics in biofloc, cage, and pond culturing system: a study on Pangasius pangasius fish gut microbiome.

Aquaculture, a rapidly expanding sector, meets the global surging demand for aquatic food. Pangasius, a highly valued freshwater species, has seen a significant increase in demand due to its adaptability and potential for high yields, making it a promising candidate for aquaculture in India. This study investigates the gut microbiome composition of Pangasius pangasius fish cultured in three different systems (biofloc, cage, and pond). Metagenomic DNA extraction and 16S rRNA gene-targeted sequencing were performed. Outcomes revealed distinct microbial compositions across culture types, with significant differences in species richness and diversity, specifically in the biofloc system, compared to cages and ponds. Taxonomic analysis identified prevalent phyla such as Firmicutes and Fusobacteriota, with varying abundances among culture systems. The genus-level analysis highlighted dominant genera such as Cetobacterium and WWE3. Functional profiling indicated differences in enzymatic activity and metabolic pathways, emphasizing each culture sample type's unique microbial community structures. Notably, the microbiota from BF samples exhibited significant differences and unique metabolic pathways compared to the microbiota from C and P samples, which showed greater similarity and shared several common metabolic pathways. These findings highlight substantial differences in microbial diversity across the culturing systems, reflecting the microbiota's ability to adapt to specific environments and their potential role in promoting fish growth within those environments. Overall, this study provides insights into the gut microbiome diversity and functionality in Pangasius pangasius across different aquaculture environments, contributing to a better understanding of host-microbe interactions and aquaculture management strategies.

Tidings from the Tides–De novo transcriptome assembly of the endemic estuarine bivalve Villorita cyprinoides

The Indian black clam Villorita cyprinoides Gray, 1825, is an economically valuable estuarine bivalve that faces challenges from multiple stressors and anthropogenic pressures. However, limited genomic resources have hindered molecular investigations into the impact of these stressors on clam populations. Here, we have generated the first transcriptomic reference datasets for V. cyprinoides to address this knowledge gap. A total of 25,040,592 and 22,486,217 million Illumina paired-end reads generated from two individuals were assembled using Trinity and rnaSPAdes. From the 47,607 transcripts identified as Coding Domain Sequences, 37,487 returned positive BLAST hits against six different databases. Additionally, a total of 14,063 Single Sequence Repeats were identified using GMATA. This study significantly enhances the genetic understanding of V. cyprinoides, a potential candidate for aquaculture that supports the livelihoods of many people dependent on small-scale fisheries. The data generated provides insights into broader genealogical connections within the family Cyrenidae through comparative transcriptomics. Furthermore, this transcriptional profile serves as baseline data for future studies in toxicological and conservation genetics.

Transcriptomic analysis of gonads in Malabar red snapper (Lutjanus malabaricus) reveals genes associated with gonad development

Malabar red snapper (Lutjanus malabaricus) is an important and high-value aquaculture species in Singapore that is attracting substantial interest and new industry investment. The consistent production of good quality eggs is an important step for establishing a selective breeding program for the species in Singapore. To achieve improved spawning outcomes, reproductive studies are needed to address the challenges in Malabar red snapper seed production, such as limited spawning success in closed culture systems. However, despite its rising profile as an aquaculture candidate and the need to improve broodstock husbandry, currently there are scarce genomic resources for the species, particularly related to genes involved in sex determination and differentiation. Herein, we report the first gonadal transcriptomes of adult L. malabaricus generated using RNA-Seq of testes (n = 6) and ovaries (n = 6). A total of 14,421 significant differentially expressed genes (DEGs) were found by comparing the gene expression profiles of ovaries and testes, including 6499 upregulated female-biased and 7922 downregulated male-biased DEGs. These DEGs included genes known to be involved in reproductive processes such as male-biased dmrt1, spat4, odf3b and sox9, and female-biased cyp19a1, zp4, sox3, bmp15 and esr1. The expression level of 16 selected DEGs were validated by RT-qPCR. This study lays the basis for further research in genes involved in sex determination and differentiation, sex control and breeding in Malabar red snapper.

Identifying potential drug targets in the kinomes of two monogenean species.

Protein kinases are enzymes involved in essential biological processes such as signal transduction, transcription, metabolism, and the cell cycle. Human kinases are targets for several drugs approved by the US Food and Drug Administration. Therefore, the identification and classification of kinases in other organisms, including pathogenic parasites, is an interesting subject of study. Monogeneans are platyhelminths, mainly ectoparasites, capable of causing health problems in farmed fish. Although some genomes and transcriptomes are available for monogenean species, their full repertoire of kinases is unknown. The aim of this study was to identify and classify the putative kinases in the transcriptomes of two monogeneans, Rhabdosynochus viridisi and Scutogyrus longicornis, and then to predict potential monogenean drug targets (MDTs) and selective inhibitor drugs using computational approaches. Monogenean kinases having orthologs in the lethal phenotype of C. elegans but not in fish or humans were considered MDTs. A total of 160 and 193 kinases were identified in R. viridisi and S. longicornis, respectively. Of these, 22 kinases, belonging mainly to the major groups CAMK, AGC, and TK, were classified as MDTs, five of which were evaluated further. Molecular docking analysis indicated that dihydroergotamine, ergotamine, and lomitapide have the highest affinity for the kinases BRSK and MEKK1. These well-known drugs could be evaluated in future studies for potential repurposing as anti-monogenean agents. The present study contributes valuable data for the development of new antiparasitic candidates for finfish aquaculture.

Histological features of the gastrointestinal tract of elongate tigerfish, Hydrocynus forskahlii (Cuvier, 1819), from Lake Albert

BackgroundThe tigerfish (Hydrocynus forskahlii) is an important food fish in different regions of Africa. As such, interest in its performance and nutritional requirements as a potential candidate for aquaculture is increasing. Characterization of the morpho-histological features and functions of the gut provides valuable insights into the feeding physiology and digestive system of fish species.ResultAn investigation of the morpho-histological features of the gastrointestinal tract of H. forskahlii captured from Lake Albert was conducted over an eight-month period. The digestive tract of H. forskahlii is characterised by a short oesophagus, well-developed and distensible stomach and moderately long intestine. The oesophagus had a higher abundance of mucous-secreting goblet cells compared to other digestive tract tissues. The stomach had a bag-like shape for swallowing large prey and was distinguishable into the cardiac, fundic and pyloric regions. Both the cardiac and fundic regions of the stomach had numerous gastric glands, whereas the pyloric region had large compound folds consisting of pseudo-stratified columnar epithelium. Many goblet cells were also observed in the mid and posterior regions of the intestine. The relative length of the gut of the H. forskahlii was 1.27 ± 0.03 cm, and it had a total of 20–22 pyloric caeca. The liver was observed to be divided in lobules by a central vein contained within connective sheets. Irregular cords of hepatocytes were also visible throughout the parenchyma.ConclusionsThe histological features of the H. forskahlii gut observed in the present study are consistent with those of carnivorous and omnivorous fish.

From Isolated Valves to a Potential Marine Living Resource: History, Documented Distribution and Sustainable Population Enhancement Possibilities of the Smooth Scallop (Flexopecten glaber) on the Romanian Coast

Until recently, the smooth scallop Flexopecten glaber (Linnaeus, 1758) was considered absent from Romanian Black Sea waters, as only isolated valves were documented on beaches of the southern coast. Yet, in 2020, the first living specimens were collected by dredging at 25 m depth in Mangalia. Moreover, in the past three years, a considerable number of live individuals were also retrieved from beam-trawling operations targeting the gastropod Rapana venosa (Valenciennes, 1846) along the Romanian coast, indicating that there is a stable population here. This remarkable expansion of F. glaber in Romanian waters may be explained as a consequence of the Black Sea’s recovery from eutrophication, reduced predatory pressure from the declining population of R. venosa and changing climate conditions. Our research aimed at using all this novel information to document for the first time the occurrence and distribution of this bivalve on the Romanian coast, also considering perspectives for the development of a new type of shellfish mariculture, avoiding any pressure on the natural stock. In total, 386 F. glaber individuals were sampled during 2020–2023, at depths between 22.5 and 33.3 m. The abundance and biomass per station oscillated between 5 and 319 specimens and 51.5 and 7377 g, respectively. A subsample of 122 specimens was preserved and analyzed in the laboratory, revealing an average shell length of 53.54 mm (±4.13 SD) and an average shell height of 49.54 mm (±3.64 SD). The smooth scallop has both ecological and economic value, which makes it a viable candidate for sustainable aquaculture by collecting spat from the most abundant areas and subsequently placing “seedlings” in the appropriate polygons for stock recovery. Ultimately, commercial exploitation from aquaculture installations can be considered, provided a permanent healthy F. glaber population is established on the Romanian coast.

Simulated cold spell: Changes of lipid metabolism on silver pomfret during cooling and rewarming

In recent decades, frequent extreme cold spells have led to fluctuations in water temperature. As poikilotherm, fish adapt to the environmental temperature through a series of physiological and metabolic regulation. Silver pomfret (Pampus argenteus) is an economical marine fish, a potential candidate for aquaculture. To investigate the impact of cold stress and subsequent rewarming on the energy metabolism of silver pomfret, we simulated an extreme cold spell by gradually lowering water temperature from 18 °C to 6 °C, followed by a gradual rise to 12 °C. The findings revealed notable trends: as the water temperature dropped to 12 °C, there was a significant increase in fatty acid content. However, upon reaching 6 °C, the condition factor (CF) decreased, accompanied by a reduction in liver mass. During the rewarming phase, severe tissue damage was observed in both muscle and liver tissues, alongside elevated AST and ALT activity. Besides, silver pomfret consumed stored fatty acids, CF, hepatosomatic index and n-3/n-6 fatty acid ratio were higher than other groups once the water temperature returned to 12 °C. Further transcriptome sequencing of the liver revealed significant enrichment in numerous metabolism-related pathways through KEGG and GO analyses. Ten differentially expressed genes (DEGs), encoding pivotal enzymes in lipid metabolism, were identified from pathways such as the PPAR signaling pathway and fatty acid degradation. Based on these results, it was hypothesized that silver pomfret shields against injury by modulating fatty acid composition. This hypothesis found validation in P. argenteus liver cells, where acsl1, cpt1 and cpt2 were identified to facilitate lipid activation and transportation. Knocking down acsl1 impacted the utilization of lipid droplets, further affirming this mechanism. This study sheds light on the adaptive strategies of economically significant fish species in confronting extreme cold spells, providing valuable insights for future reference.

Molecular identification of intertidal rock oyster species in north-eastern Australia reveals new candidates for aquaculture

Oyster aquaculture in Australia is currently centred on two species, Saccostrea glomerata (Gould, 1850) and Magallana gigas (Thunberg, 1793) which are both susceptible to disease. Disease outbreaks have caused significant losses to the industry and there is currently an appetite for diversification to mitigate risk. Development of other, native oyster species for aquaculture is limited by a poor understanding of their biodiversity and distribution, which is primarily due to the difficulty in distinguishing species based on morphology alone. In this study we sampled intertidal rock oysters from 19 localities in north-eastern Australia and performed phylogenetic analyses based on partial COI and 16S mitochondrial markers. A total of 14 distinct oyster lineages (most likely representing distinct species) were identified from the 357 specimens collected and sequenced. In total, we report the presence of 8 Saccostrea lineages, 4 Ostreinae lineages, one Magallana lineage (Magallana bilineata (Röding, 1798), a recent introduction), and one Talonostrea lineage (likely undescribed). A number of these lineages have broad distributions and attain large sizes, and several are currently cultured in other parts of the world. Although morphological identification is challenging we argue that the large size of the tropical black-lip oyster, Saccostrea lineage J, enables it to be definitively identified as Saccostrea spathulata (Lamarck 1819), thus providing taxonomic certainty for this commercially important species. The identification of these oyster lineages and their distributions is a fundamental step towards development of viable alternatives for oyster aquaculture in the region.

Generational breeding gains in a new species for aquaculture, the Australasian snapper (Chrysophrys auratus)

Selective breeding for improved trait performance is a promising approach for developing new species for food production. Globally, a shortage of livestock species presents a significant bottleneck, and this is particularly pronounced for the aquaculture sector. In New Zealand, the Australasian snapper (Chrysophrys auratus) is a potential candidate for aquaculture, and a breeding programme was started in 2004. Here we assess the performance of the most recent F4 cohort in terms of growth and survival against 1) previous generations and 2) unselected offspring from wild broodstock over the first 6 months. First, we detected generational gains over the entirety of the breeding programme in growth, averaging 11.4% for length and 81.1% for weight over 3 years, and detected a strong seasonal Specific Growth Rate (SGR) increase during summer and a general decrease of growth with age. Second, when growing the F4 and F1 cohort side by side, we found a consistent pattern of superior performance, less growth heterogeneity, and a higher condition factor within the F4 population. Notably, these data revealed breeding gains of 4.9% in survival, 10.5% in length and 41.4% in weight for F4 snapper over the first 6 months from hatching. Together these results indicate that domestication gains and genetic improvement can strengthen the potential of snapper as a candidate to diversify and grow aquaculture in New Zealand.

Use of Cryopreserved Sperm of Grass Carp (Ctenopharyngodon idella) for Seed Production at the Hatchery Level of Bangladesh-A Need for Development of Germplasm Repositories.

Grass carp (Ctenopharyngodon idella), a freshwater nonnative fish species, is a potential aquaculture candidate in Bangladesh. The seed of the species is produced in the hatcheries by hypophysation, but the quality of seedstock of grass carp is deteriorated due to inbreeding, negative selection, and interspecific introgression among fishes. To increase the availability of quality seed and best genetic traits of grass carp, this study dealt with finding suitable conditions of sperm cryopreservation protocols and evaluated the effectiveness of cryopreserved sperm through breeding trials of C. idella. A broodstock population was developed from fingerlings imported from China by the Bangladesh Department of Fisheries. Sperm was collected from hormone-induced mature males, with an estimated concentration of 2.4 ± 0.3 × 1010 cells/mL and a pH of 8.3 ± 0.2. Sperm motility was evaluated in different concentrations of NaCl solution. The highest motility (96% ± 1%) and longest motility duration (22 ± 1 min) were achieved at 0.4% of NaCl (128 mOsmol/kg). The toxicity of DMSO and methanol at concentrations of 5%, 10%, and 15% was evaluated for 5-40 min using Alsever's solution and egg yolk citrate. The highest motility was achieved during 5 and 10 min of incubation with cryoprotectants at 5% and 10%. Alsever's solution with 10% DMSO at 1:9 dilution with sperm produced the highest equilibration motility (93% ± 2%) and when cooled at 10°C/min yielded the highest postthaw motility (85% ± 3%). Fertilization of 24% ± 3% to 51% ± 2% and hatching of 18% ± 2% to 41% ± 2% were achieved by using cryopreserved sperm in six selected private hatcheries. The fertilization rate for fresh sperm sourced from hatchery-reared males was 64% ± 5% to 85% ± 3%, and the hatching rate ranged from 53% ± 6% to 74% ± 5%. Thus, the cryopreservation protocol of C. idella sperm was found to be feasible for fry production at commercial hatcheries, but further research is needed to improve the fertilization and hatching rates.