Background: Accelerating climate change has intensified hypoxic events in aquatic ecosystems. In aquaculture, high stocking densities make farmed fish particularly vulnerable to these episodes, leading to negative economic repercussions. This has driven interest in selective breeding for hypoxia tolerant fish as a potential mitigation strategy. In this context, the present systematic review synthesizes and critically evaluates current knowledge on genetic variation associated with hypoxia tolerance in farmed fish species. A literature search was conducted in Scopus and Web of Science following the Preferred Reporting Items for Systematic reviews and Meta-Analyses 2020 guidelines. Results: In total, 964 articles were identified, of which 41 met the inclusion criteria, encompassing 26 species and three hybrid lines. Among the farmed fish, the blunt snout bream, rainbow trout, common carp, and Nile tilapia were the most extensively studied. The most commonly used metrics to assess hypoxia tolerance included: (1) time or oxygen level at which loss of equilibrium occurs, (2) survival time or status (alive or dead), and (3) critical oxygen partial tension measured via respirometry. Substantial phenotypic variability in hypoxia tolerance across families, strains, gynogenetic lines, growth transgenic lines, hybrid lines, and species was reported in most studies. Although single nucleotide polymorphism associated with hypoxia tolerance were identified in several studies, heritability estimates were reported in only three of these, ranging from 0.28 to 0.65, underscoring the need for further research to strengthen the basis for selective breeding applications. Furthermore, candidate genes identified across studies were involved in a wide range of biological processes underlying hypoxia responses, including hypoxia signaling and its regulation (HIF-related genes and their inhibitors, such as HIF1αn ), angiogenesis, energy metabolism, oxidative stress defense, erythropoiesis, ion regulation, DNA repair, and immune and apoptotic processes. Conclusions: As aquatic environments become more hypoxic, the findings of this review underscore the potential of the inherent genetic diversity for hypoxia tolerance present in farmed fish populations. In this context, genomic selection and gene editing emerge as promising tools for developing hypoxia tolerant fish lines. Further research under production conditions is essential before implementation of these approaches in practical in breeding programs, particularly to evaluate the most appropriate trait(s) for measuring hypoxia tolerance, potential correlated responses with other economically important traits, and the overall feasibility at an industry scale.

The Chub mackerel (Teleostei: Scombridae) supports an important fishery in the Southeastern Pacific, however, its population genetics status is currently unknown. In the present study the population genetic structure, gene flow and historical demography of this resource in the Northern Humboldt Current System were examined. Samples were collected between 2103 and 2014 from three fishing points off the Peruvian coast (Paita, Ventanilla and Ilo) and analyzed using mitochondrial D-Loop region sequences. A total of 29 polymorphic sites and 35 haplotypes were found in 72 individuals. Moderate haplotype diversity and very low levels of nucleotide diversity were found. Analysis of gene flow showed high levels of connectivity among sampling areas. Analysis of molecular variance, pairwise comparisons and genetic differentiation tests confirmed the lack of genetic structuring. These analyses suggest that analyzed sampling locations can be considered as a single gene pool. Migratory behavior, the high dispersal potential of early stages and the lack of oceanographic barriers can explain its genetic homogeneity along the Peruvian sea. The historical demography was also examined. Neutrality testing, mismatch distribution and Bayesian skyline plot suggested a population expansion scenario that took place during the Late Pleistocene. This study provides novel information about population genetics of the chub mackerel from the Southeastern Pacific.

Nudibranchs, as a group, have received limited attention in terms of scientific study along the coastline of Peru. Here, an updated and comprehensive list of nudibranch species found in the Peruvian sea is presented, compiled through an extensive review of relevant literature. This compilation encompasses a total of 31 species, classified into two suborders, 10 superfamilies, 20 families, and 28 genera. With respect to the biogeographic provinces along the Peruvian coast, 23 species inhabit the Warm Temperate Southeastern Pacific province, 18 species occur in the Tropical Eastern Pacific province, and 10 species are found in both provinces, crossing the transitional zone between them. In terms of distribution patterns, two species exhibit a cosmopolitan distribution (Glaucus atlanticusandFiona pinnata), while two species display a circumtropical distribution (Cephalopyge trematoidesandPhylliroe bucephala). One species exhibits a bipolar distribution in the Eastern Pacific and possesses an amphi-South American distribution (Rostanga pulchra). Additionally, six species exhibit an amphi-South American distribution (Rostanga pulchra,Diaulula punctuolata,Doto uva,Tyrinna evelinae,Tyrinna delicata, andDoris fontainii), and two species are endemic to Peru (Corambe mancorensisandFelimare sechurana). This study provides comprehensive information on biogeographical aspects, geographical distributions, and taxonomic updates within the nudibranch species documented in Peru. Furthermore, we discuss the status of species listed in previous literature that have not been confirmed by collections, referring to them as potentially occurring species.