Kelli Anderson

Tasmanian Atlantic salmon broodstock may be conditioned in flow‐through (FT) systems where water quality fluctuates and temperatures approach their upper limit of thermal tolerance, or in recirculating aquaculture systems (RAS) where conditions are comparatively cool and stable. The impact of broad conditioning approach on the molecular cargo of salmon eggs has never been explored in dynamic commercial settings. Therefore, this study aimed to characterise the reproductive features of broodstock conditioned using different commercial approaches and determine whether the fatty acid (FA) profiles of muscle, oocytes and eggs varied between groups during vitellogenesis and at stripping. The collective conditioning approach had a marked impact on the somatic and reproductive dynamics of female salmon broodstock, and the eggs produced by each group of fish were fundamentally different in terms of their FA composition. Of particular note is the increased maternal investment of saturated FAs (mg.g⁻¹) and monounsaturated FAs (percent and mg.g⁻¹) by FT‐based eggs, and the higher n3 polyunsaturated FA (percent and mg.g⁻¹), docosahexaenoic acid (DHA, percent and mg.g⁻¹), arachidonic acid (ARA, percent), eicosapentaenoic acid (EPA, percent), n3:n6 ratio and ARA:EPA ratio of RAS‐based eggs. These metrics combined with the apparently higher prevalence of neural development and survival of RAS embryos suggest that RAS eggs were of higher quality. On the other hand, there is evidence to suggest that FT broodstock attempt to prepare their offspring for a (presumably) challenging early life environment by producing larger eggs that are proportionally rich in short‐chain FAs and contain a higher total quantity of FAs per egg.

Cobia (Rachycentron canadum) is the only member of the Rachycentridae family and exhibits considerable sexual dimorphism in growth rate. Sex determination in teleosts has been a long-standing basic biological question, and the molecular mechanisms of sex determination/differentiation in cobia are completely unknown. Here, we reported 2 high-quality, chromosome-level annotated male and female cobia genomes with assembly sizes of 586.51 Mb (contig/scaffold N50: 86.0 kb/24.3 Mb) and 583.88 Mb (79.9 kb/22.5 Mb), respectively. Synteny inference among perciform genomes revealed that cobia and the remora Echeneis naucrates were sister groups. Further, whole-genome resequencing of 31 males and 60 females, genome-wide association study, and sequencing depth analysis identified 3 short male-specific regions within a 10.7-kb continuous genomic region on male chromosome 18, which hinted at an undifferentiated sex chromosome system with a putative XX/XY mode of sex determination in cobia. Importantly, the only 2 genes within/between the male-specific regions, epoxide hydrolase 1 (ephx1, renamed cephx1y) and transcription factor 24 (tcf24, renamed ctcf24y), showed testis-specific/biased gene expression, whereas their counterparts cephx1x and ctf24x, located in female chromosome 18, were similarly expressed in both sexes. In addition, male-specific PCR targeting the cephx1y gene revealed that this genomic feature is conserved in cobia populations from Panama, Brazil, Australia, and Japan. The first comprehensive genomic survey presented here is a valuable resource for future studies on cobia population structure and dynamics, conservation, and evolutionary history. Furthermore, it establishes evidence of putative male heterogametic regions with 2 genes playing a potential role in the sex determination of the species, and it provides further support for the rapid evolution of sex-determining mechanisms in teleost fish.

Proactive and coordinated action to mitigate and adapt to climate change will be essential for achieving the healthy, resilient, safe, sustainably harvested and biodiverse ocean that the UN Decade of Ocean Science and sustainable development goals (SDGs) seek. Ocean-based mitigation actions could contribute 12% of the emissions reductions required by 2030 to keep warming to less than 1.5 ºC but, because substantial warming is already locked in, extensive adaptation action is also needed. Here, as part of the Future Seas project, we use a “foresighting/hindcasting” technique to describe two scenarios for 2030 in the context of climate change mitigation and adaptation for ocean systems. The “business-as-usual” future is expected if current trends continue, while an alternative future could be realised if society were to effectively use available data and knowledge to push as far as possible towards achieving the UN SDGs. We identify three drivers that differentiate between these alternative futures: (i) appetite for climate action, (ii) handling extreme events, and (iii) climate interventions. Actions that could navigate towards the optimistic, sustainable and technically achievable future include: (i) proactive creation and enhancement of economic incentives for mitigation and adaptation; (ii) supporting the proliferation of local initiatives to spur a global transformation; (iii) enhancing proactive coastal adaptation management; (iv) investing in research to support adaptation to emerging risks; (v) deploying marine-based renewable energy; (vi) deploying marine-based negative emissions technologies; (vii) developing and assessing solar radiation management approaches; and (viii) deploying appropriate solar radiation management approaches to help safeguard critical ecosystems.

Ambient temperature modulates reproductive processes, especially in poikilotherms such as teleosts. Consequently, global warming is expected to impact the reproductive function of fish, which has implications for wild population dynamics, fisheries and aquaculture. In this extensive review spanning tropical and cold‐water environments, we examine the impact of higher‐than‐optimal temperatures on teleost reproductive development and physiology across reproductive stages, species, generations and sexes. In doing so, we demonstrate that warmer‐than‐optimal temperatures can affect every stage of reproductive development from puberty through to the act of spawning, and these responses are mediated by age at spawning and are associated with changes in physiology at multiple levels of the brain–pituitary–gonad axis. Response to temperature is often species‐specific and changes with environmental history/transgenerational conditioning, and the amplitude, timing and duration of thermal exposure within a generation. Thermally driven changes to physiology, gamete development and maturation typically culminate in poor sperm and oocyte quality, and/or advancement/delay/inhibition of ovulation/spermiation and spawning. Although the field of teleost reproduction and temperature is advanced in many respects, we identify areas where research is lacking, especially for males and egg quality from “omics” perspectives. Climate‐driven warming will continue to disturb teleost reproductive performance and therefore guide future research, especially in the emerging areas of transgenerational acclimation and epigenetic studies, which will help to understand and project climate change impacts on wild populations and could also have implications for aquaculture.

The collection and presentation of accurate reproductive data from wild fish has historically been somewhat problematic, especially for serially spawning species. Therefore, the aim of the current study was to develop a novel method of assessing female spawning status that is robust to variation in oocyte dynamics between specimens. Atlantic cod (Barents Sea stock) were used to develop the new ‘ultrametric’ method, that is based on the progressive depletion of the vitellogenic oocyte pool relative to the rather constant previtellogenic oocyte (PVO) pool. Fish were subsequently partitioned into one of four categories that accurately reflected changes in their oocyte size frequency distribution characteristics and gonadosomatic index throughout spawning. The ultrametric method overcomes difficulties associated with presence of bimodal oocyte distributions, oocyte tails, lack of clear hiatus region, and presence of free ova, and can be implemented at a single sampling point. Much of the workflow is fully automated, and the technique may circumvent the need for histological analysis depending on the desired outcome. The ultrametric method differs from the traditional autodiametric method in that PVOs can be separated by ultrasonication and then enumerated, and ovarian homogeneity is not a mandatory requirement per se. The method is designed for determinate spawners but might be extended to include indeterminate spawners.

The giant grouper Epinephelus lanceolatus is an ecologically vulnerable species with high market demand. However, efforts to improve larval husbandry are hindered by a lack of knowledge surrounding larval developmental physiology. To address this shortfall, a transcriptomic approach was applied to larvae between 1 and 14 days post hatch (dph) to characterise the molecular ontogenesis of genes that influence appetite and digestion. Appetite regulating factors were detected from 1 dph, including neuropeptide Y, nesfatin‐1, cocaine and amphetamine regulated transcript, cholecystokinin and pituitary adenylate cyclase activating peptide and the expression level of several genes changed sharply with the onset of exogenous feeding. The level of expression for proteases, chitinases, lipases and amylases typically followed one of two expression patterns, a general increase as development progressed, or an inverted U‐shape with maximal expression at c. 6 dph. Similarly, the tendency among both expression patterns was for the level of expression to increase around the time of mouth‐opening. There was also evidence to suggest the presence of putative isoforms for several digestion‐related genes. We have provided an insight into appetite‐regulation and digestive processes in groupers during early larval development and have developed a transcriptomic database that will aid future efforts to rear this species in an aquaculture setting.