Environmental Biology of Fishes最新文献

The Atlantic tarpon Megalops atlanticus is a tropical-subtropical fish that occupies mangrove and salt marsh habitats during the first year of life. Diet during the first few months of life can have substantial effects on growth and survival of fishes. The purpose of our study was to examine the diet of age-0 tarpon in the North Inlet-Winyah Bay estuarine system, located near the northern extent of their distribution in the western Atlantic Ocean. We examined stomach contents to characterize tarpon diet and relate tarpon feeding to water temperature. The most important prey items based on the frequency of occurrence and proportion by weight indices were small fishes and crustaceans, whereas copepods were the most important prey based on the proportion by number index. Small age-0 tarpon ((le) 100 mm) consumed small crustaceans (copepods) while large age-0 tarpon (> 100 mm) consumed larger crustaceans (shrimp) and age-0 tarpon of all sizes consumed fish. Most tarpon with empty stomachs were collected at temperatures < 25 °C, whereas most tarpon with prey in their stomach were collected at temperatures > 25 °C. The proportion of tarpon having at least one prey item in their stomach contents was greatest around 28 °C and declined at lower and higher water temperatures. Salt marsh habitats in the North Inlet-Winyah Bay estuarine system provide suitable food resources for age-0 tarpon. As water temperatures increase and tropical species, such as tarpon, expand their range, these coastal nursery habitats may become more important for tarpon growth and recruitment to the spawning stock.

One of the most unique examples of adaptation to extreme environments is exemplified by diapauses (I, II and III) in annual killifish embryos. We aimed to understand the molecular mechanisms involved in the regulation of these arrests. In this context, we first comprehensively analysed the expression of genes using a transcriptomic approach to distinguish between two developmental trajectories: diapause induction and non-diapause induction. We focused on the process of diapause I induction by comparing the mRNA profiles at the maternal stage with those of diapause I-induced embryos, non-diapause I-induced embryos and embryos that had exited diapause I. Our analysis revealed approximately seven hundred transcripts that were differentially and exclusively expressed upon the induction of diapause I. The Gene Ontology (GO) categories of the gene-specific transcriptional regulator group, RNA metabolism, cytoskeletal protein and scaffold/adaptor proteins exhibited the highest representation among differentially expressed genes (DEGs) and coexpression analysis. Remarkably, the identification of different homeodomain transcription factors, cell cycle regulators and RNA processing/regulators as DEGs suggests that these regulators play important roles in Garcialebias charrua diapause I induction. Consistent with the results of the DEG analysis, the results of the Clust coexpression analysis revealed 5 and 3 patterns of diapause I-induced gene upregulation and downregulation, corresponding to 3939 and 1250 genes, respectively. Comparative expression analysis of genes and signalling pathways reported to contribute to diapauses in other species revealed that insulin/IGF, vitamin D, Wnt, polycomb and heat shock proteins are also involved in diapause I induction in annual killifish.

In the context of warming freshwater habitats, protection of Atlantic salmon populations requires an understanding of the effects of temperature on somatic growth during the juvenile life stage. However, quantifying the effect of temperature on growth is challenging given differences among methodologies, metrics of growth, and their underlying assumptions. Using short term studies (2000–2002) in two Canadian populations of wild Atlantic salmon (Margaree and Miramichi rivers), we investigate whether different hierarchical modeling approaches influence the derivation of temperature-growth relationships, by contrasting seasonal growth trajectories (von Bertalanffy; VBGF) to size-at-age data models built with instantaneous growth rates. Size-at-age data analysed seasonally with the VBGF framework failed to detect an effect of temperature, whereas instantaneous growth rates from the same dataset were strongly related to temperature metrics. However, instantaneous growth rates cannot be used to extrapolate predictions into meaningful metrics for fisheries management (e.g., size at the end of the growing season). Nevertheless, we show that size at the end of the growing season can be predicted with VBGF models accounting for site-level variation, which in turn are related to temperature metrics, as observed for instantaneous growth rates. Taken together, these results show that combining these two approaches (size-at-age, growth rates) can circumvent their intrinsic drawbacks and reveal essential ecological patterns that may otherwise remain undetected. In cases where instantaneous growth rates are not available, relating predicted size-at-age from hierarchical VBGF to temperature provides an interesting alternative for detecting subtle environmental effects, even if the VBGF parameters or its residuals are unrelated to temperature metrics.

We provide an alternative interpretation for the “whitish film” that covered the young white shark observed with an aerial drone in a paper published recently (Gauna and Sternes, Environ Biol Fish 107:249–254, 2024). The paper claimed that this whitish film was a leftover intrauterine substance (e.g., uterine milk, which is a maternal secretion to nourish embryos), thus suggesting that the individual was a newborn. However, we are skeptical of this interpretation for the following reasons: (1) our previous studies showed that the secretion of intrauterine substances in white sharks ceases in mid-gestation and, (2) even if the secretion continues until birth, the substance is unlikely to be retained on the skin for a long time after birth. Based on data from Lamna ditropis, a close relative of the white shark, we hypothesize that the whitish film is an embryonic epithelium that covers the surface of skin denticles. This reinterpretation does not alter but reinforces the major conclusion of (Gauna and Sternes, Environ Biol Fish 107:249–254, 2024) that the individual sighted is a newborn.

Natural environments vary, and organisms cope with this variation in two general ways: local adaptation and phenotypic plasticity, although these strategies often overlap and interact. This study explored how local adaptation, phenotypic plasticity, and their interactions shaped phenotypic variation in populations of Poecilia mexicana, an extremophile fish living in adjacent but ecologically divergent habitats. By comparing populations from the wild with fish raised in a common-garden environment, we evaluated how genetic differentiation between populations and plasticity contributed to the phenotypic variation observed in nature. We quantified variation in the size of six organs (brain, eyes, gills, heart, liver, and gastrointestinal tract), routine metabolic rate, and body shape. We found evidence for genetic differences between populations impacting the expression of the majority of traits, in addition to or in interaction with phenotypic plasticity and other predictor variables. Overall, our results suggest that trait divergence between populations was at least in part driven by evolutionary change and not just merely by plasticity induced by environmental differences between habitats. Future studies will have to rigorously test whether evolutionary divergence was caused by natural selection and what traits represent adaptations to the different ecological conditions.

In a laboratory experiment, we quantified microhabitat use of small yellow-phase American eels (Anguilla rostrata, n = 130, 224–338 mm TL) conditional on five benthic substrate types common to rivers within their geographic range. During nine, 4-day trials replicated with three aquaria, American eels were given a choice to burrow into five equally available benthic substrates: cobble (90–256 mm), gravel (4–16 mm), sand (0.125–1 mm), silt/clay (< 0.0625 mm), and leaf pack. Five American eels were used per aquarium for each trial, and individuals were used one time only. All eels were injected with PIT tags prior to the study, which allowed for determination of lengths and otolith-based ages of each individual following each trial. Leaf pack was selected with a significantly higher probability than other substrates (63 of 130 individuals). However, other substrates were also used (cobble, 21 of 130; silt/clay, 18 of 130; gravel, 16 of 130; and sand, 12 of 130). Length and age covariates were not associated with substrate selection. Selection of leaf pack habitat supports the importance of forested riparian zones and terrestrial organic material to yellow-phase American eels in riverine systems.

The cururu stingray (Potamotrygon wallacei) is an endemic species from the Negro River basin, Brazil. There are only a few studies describing the integument morphology and tissue repair in potamotrygonins. Therefore, this study aimed to describe the integument morphology of P. wallacei in different body portions and report the tissue repair in an injury observed on the edge of the pectoral fin in one individual. Four specimens of P. wallacei were collected in the Mariuá Arquipelago, near to the municipality of Barcelos, Amazonas. Samples of the integument were taken from the dorsal, tail and ventral region and from the edge of the pectoral fin. Subsequently, these samples were submitted to histological processes and stained with hematoxylin–eosin, PAS and Alcian Blue 2.5. In all the body portions, the epidermis comprises a non-keratinized stratified squamous epithelium with mucous and sacciform cells that secrete mucosubstances. In the epidermis, chromatophores are responsible for the brown coloration of this species. The epidermis is thickest in the dorsal region. The dermis comprises two strata: the stratum laxum, with thin collagen fibers, which is thicker on the ventral surface. The stratum compactum, dense in thick collagen fibers, is thicker in the tail region. The repaired pectoral fin showed a thin epidermis with a reduced number of mucous cells and restored cartilaginous radials. The integument of P. wallacei is similar to that described for other elasmobranchs and our findings suggest that this species has the ability to regenerate its integumentary tissues after a potential injury.

Hatching corresponds to the moment an individual leaves its egg envelope. Yet, hatching has scarcely aroused the interest of biologists, and the question posed here, ‘why do larvae hatch when they do?’ appears to have been rarely asked. In this proof-of-concept study, we tested the hypothesis that fish larvae hatch when a specific ratio between egg surface area (ESA) and larval surface area (LSA) is reached, irrespective of egg diameter and abiotic factors. An estimated mean ratio of 1: 1.52 (CI = 1.39–1.63) was obtained from the eggs of 33 species of teleosts, with diameters ranging from 0.63 to 5.7 mm. We assume that this ratio has a value beyond which the oxygen supply through the egg surface cannot cope with the oxygen requirements of the embryo. The detailed ecological consequences are unknown but can be expected to impact fisheries and aquaculture negatively.

The distinct origin and hydrological characteristics of reservoirs, shaped by fluctuating water levels and seasonal variations, play a crucial role in determining aquatic species assemblages across diverse limnological zones. This study aimed to analyze fish and crayfish assemblages in the nearshore area of a canyon-shaped Mediterranean reservoir, seeking to identify seasonal and spatial convergent patterns and infer the factors influencing them. Samplings were conducted at five stations along the longitudinal profile of the reservoir at depths around 7 m using gillnets and hoops nets. A seasonal pattern emerged regarding species abundance and biomass, with higher values recorded during the warmer period. Additionally, a spatial trend was observed, indicating higher species abundance in the middle part of the reservoir and lower abundance near the dam, particularly during the colder period. Water transparency, temperature, and the distance from the dam were identified as the most significant factors affecting species assemblages in terms of abundance and biomass. This research provides valuable insights into the intricate interplay between environmental factors, seasonal changes, and the assemblages of aquatic species in a Mediterranean reservoir, contributing to our understanding of its ecological dynamics.

Yellow Perch (Perca flavescens) inhabit both nearshore and coastal wetland habitats of the Laurentian Great Lakes throughout their lifetime and are known to exhibit different movement life histories. However, uncertainty persists in the spatial extent of this variation and in the duration of habitat use. To explore these uncertainties, we used a multi-metric approach that included water and otolith microchemistry and tissue stable isotope ratios (δ¹³C, δ¹⁵N). The ratio of manganese to calcium in otoliths was used to identify transitional movements between nearshore Lake Ontario and wetland habitats while carbon and nitrogen tissue isotope ratios revealed variable duration of wetland inhabitance. Our research suggests that the multi-metric approach was useful for addressing questions that could not be answered by one method alone. Our results demonstrate individual differences in duration of coastal wetland habitat residence among Yellow Perch, which may influence their susceptibility to recreational harvest. As Yellow Perch are an important species of consideration for management agencies such as the Great Lakes Fishery Commission, exposing such diversity is important when considering the potential for differential contributions of individuals with variable movement life histories to overall population stability and resilience over time.