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Although being some of the most valuable and heavily exploited wild organisms, few fisheries species have been studied at the wholegenome level. This is especially the case in New Zealand, where genomics resources are urgently needed to assist fisheries management. Here, we generated 55 Gb of short Illumina reads (92× coverage) and 73 Gb of long Nanopore reads (122×) to produce the first genome assembly of the marine teleost tarakihi [Nemadactylus macropterus (Forster, 1801)], a highly valuable fisheries species in New Zealand. An additional 300 Mb of Iso-Seq reads were obtained to assist in gene annotation. The final genome assembly was 568 Mb long with an N50 of 3.37 Mb. The genome completeness was high, with 97.8% of complete Actinopterygii Benchmarking Universal Single-Copy Orthologs. Heterozygosity values estimated through k-mer counting (1.00%) and bi-allelic SNPs (0.64%) were high compared with the same values reported for other fishes. Iso-Seq analysis recovered 91,313 unique transcripts from 15,515 genes (mean ratio of 5.89 transcripts per gene), and the most common alternative splicing event was intron retention. This highly contiguous genome assembly and the isoform-resolved transcriptome will provide a useful resource to assist the study of population genomics and comparative eco-evolutionary studies in teleosts and related organisms. [ABSTRACT FROM AUTHOR]

Tarakihi (Nemadactylus macropterus) is a demersal fish that supports valuable commercial, recreational, and customary fisheries in New Zealand. However, little is known about its stock structure. The population genetic structure, genetic diversity, and demographic history of N. macropterus were investigated using the hypervariable region one of the mitochondrial control region. 370 samples from 14 locations around New Zealand were collected. While weak genetic breaks were detected between Hawke's Bay and East Northland and between the west and east coasts of South Island, no clear genetic structure was detected for the overall New Zealand area (ФST = 0.002, P = 0.18), indicative of a panmictic genetic structure. N. macropterus display a high level of genetic diversity and appear to have a historically large and stable population with a long evolutionary history. Bayesian skyline analysis indicates that the historic population has gone through two expansions, likely caused by repeated glacial cycles during the second half of the Pleistocene. The addition of 15 king tarakihi samples (Nemadactylus n.sp.) collected from the Three Kings Islands showed a clear genetic differentiation between the two morphotypes. These findings can inform the future management of N. macropterus and N. n.sp. to ensure a sustainable harvest. [ABSTRACT FROM AUTHOR]

Background: The genetic control of sex determination in teleost species is poorly understood. This is partly because of the diversity of mechanisms that determine sex in this large group of vertebrates, including constitutive genes linked to sex chromosomes, polygenic constitutive mechanisms, environmental factors, hermaphroditism, and unisexuality. Here we use a de novo genome assembly of New Zealand silver trevally (Pseudocaranx georgianus) together with sex-specific whole genome sequencing data to detect sexually divergent genomic regions, identify candidate genes and develop molecular makers. Results: The de novo assembly of an unsexed trevally (Trevally_v1) resulted in a final assembly of 579.4 Mb in length, with a N50 of 25.2 Mb. Of the assembled scaffolds, 24 were of chromosome scale, ranging from 11 to 31 Mb in length. A total of 28,416 genes were annotated after 12.8 % of the assembly was masked with repetitive elements. Whole genome re-sequencing of 13 wild sexed trevally (seven males and six females) identified two sexually divergent regions located on two scaffolds, including a 6 kb region at the proximal end of chromosome 21. Blast analyses revealed similarity between one region and the aromatase genes cyp19 (a1a/b) (E-value < 1.00E-25, identity > 78.8 %). Males contained higher numbers of heterozygous variants in both regions, while females showed regions of very low read-depth, indicative of male-specificity of this genomic region. Molecular markers were developed and subsequently tested on 96 histologically-sexed fish (42 males and 54 females). Three markers amplified in absolute correspondence with sex (positive in males, negative in females). Conclusions: The higher number of heterozygous variants in males combined with the absence of these regions in females support a XY sex-determination model, indicating that the trevally_v1 genome assembly was developed from a male specimen. This sex system contrasts with the ZW sex-determination model documented in closely related carangid species. Our results indicate a sex-determining function of a cyp19a1a-like gene, suggesting the molecular pathway of sex determination is somewhat conserved in this family. The genomic resources developed here will facilitate future comparative work, and enable improved insights into the varied sex determination pathways in teleosts. The sex marker developed in this study will be a valuable resource for aquaculture selective breeding programmes, and for determining sex ratios in wild populations. [ABSTRACT FROM AUTHOR]

Background. Functional groups serve two important functions in ecology: they allow for simplification of ecosystem models and can aid in understanding diversity. Despite their important applications, there has not been a universally accepted method of how to define them. A common approach is to cluster species on a set of traits, validated through visual confirmation of resulting groups based primarily on expert opinion. The goal of this research is to determine a suitable procedure for creating and evaluating functional groups that arise from clustering nominal traits. Methods. To do so, we produced a species by trait matrix of 22 traits from 116 fish species from Tasman Bay and Golden Bay, New Zealand. Data collected from photographs and published literature were predominantly nominal, and a small number of continuous traits were discretized. Some data were missing, so the benefit of imputing data was assessed using four approaches on data with known missing values. Hierarchical clustering is utilised to search for underlying data structure in the data that may represent functional groups. Within this clustering paradigm there are a number of distance matrices and linkage methods available, several combinations of which we test. The resulting clusters are evaluated using internal metrics developed specifically for nominal clustering. This revealed the choice of number of clusters, distance matrix and linkage method greatly affected the overall within- and between- cluster variability. We visualise the clustering in two dimensions and the stability of clusters is assessed through bootstrapping. Results. Missing data imputation showed up to 90% accuracy using polytomous imputation, so was used to impute the real missing data. A division of the species information into three functional groups was the most separated, compact and stable result. Increasing the number of clusters increased the inconsistency of group membership, and selection of the appropriate distance matrix and linkage method improved the fit. Discussion. We show that the commonly used methodologies used for the creation of functional groups are fraught with subjectivity, ultimately causing significant variation in the composition of resulting groups. Depending on the research goal dictates the appropriate strategy for selecting number of groups, distance matrix and clustering algorithm combination. [ABSTRACT FROM AUTHOR]

The mechanoreceptive lateral line system in fishes detects hydrodynamic stimuli and plays a critical role in many fundamental behaviours, including orientation to water currents and the detection of stationary objects, prey and predators. Interspecific variation in lateral line structure may result from a process of functional adaptation, with the background level of hydrodynamic activity proposed as an important selective pressure. Here we use the eight species of the ecologically diverse New Zealand marine triplefin fish of the genus Forsterygion and one species from the sister genus Notoclinops to investigate interspecific differences in lateral line morphology and to assess the relationship between lateral line characteristics and exposure to wave energy (fetch/depth ratio). Overall, the results show that lateral line traits are divergent between species, and these differences could in part be related to the wave exposure of the habitats that the species occupy. Specifically, numbers of canal neuromasts differed significantly between species, and most canal groupings increased in neuromast number with fetch/depth ratio, while the number and area of some superficial neuromast groupings decreased significantly with exposure. Distribution of superficial neuromasts along the trunk in the semi-pelagic and paedomorphic species F. maryannae differed from the other, demersal species, which may be associated with the unique lifestyle of this species and/or developmental processes. Canal architecture also differed considerably between species, but displayed no relationship with fetch/depth ratio. The results from this study indicate that some interspecific differences in lateral line organs may be a by-product of selection for habitat divergence. Future work should explore additional causal factors that might have influenced the evolution of lateral morphology in these species, including phylogenetic and allometric effects. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

• Juvenile fish can act as sensitive bioindicators of harbour quality. • To test this, we analysed metabolite profiles of fish using metabolomics. • Cysteine and GABA reflected a turbidity gradient among and within harbours. • Metabolomics was more sensitive at detecting differences than traditional methods. • Thus, fish metabolite levels are a sensitive indicator of environmental conditions. Estuarine habitats contribute disproportionately as nursery habitats for marine fish, yet are amongst the most anthropogenically degraded ecosystems on Earth. Juvenile fish growing in urbanised estuarine habitats are subject to a mosaic of stressors, thus development of higher resolution methods to gain a more complete assessment of fish responses is vital. Accordingly, this study provides the first assessment of metabolomic profiling as a new bioindicator of habitat quality for juvenile fish. We matched traditional bioindicator methods (fish growth rates) with metabolomic profiles in juvenile snapper (Chrysophrys auratus), a culturally and commercially important species across Australia and New Zealand. Juvenile snapper were collected from, and within, harbour sites occupying a gradient in turbidity, a significant stressor for this species that is known to result in reduced weight, mortality and deleterious physiological responses. We found that fish growth assessed using otolith increments was not reflective of the turbidity gradient with little discrimination among sites. However, metabolomic profiling was highly sensitive and reproducible, with 100% accuracy in discriminating fish from harbours with differing turbidity. These differences in metabolic profiles were largely driven by metabolites and pathways involved in energy production, processes of growth, or the immune response. In particular, the amino acids Cysteine and 4-aminobutyric acid (GABA), linked to growth and development in snapper, were elevated in juveniles from more pristine harbours, and offer promising candidates for use as a biomarker of habitat quality in this species. Thus, we show that metabolomic approaches can uncover site differences that traditional and more coarse methods were unable to detect. This work provides a novel baseline for the use of metabolomic profiling on wild-caught snapper to inform management and conservation decisions, with the potential to identify biomarkers reflective of habitat quality. [ABSTRACT FROM AUTHOR]