Environmental Biology of Fishes最新文献

Anadromous river herring populations, collectively alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), have experienced a multi-century decline in abundance and distribution. These declines have been attributed in part to anthropogenic threats in freshwater ecosystems (e.g., habitat fragmentation, overharvest, water pollution, watershed development). An understanding of variability in juvenile productivity and growth is critical to developing restoration approaches. We characterized variability in juvenile river herring growth among 11 freshwater lakes in the northeastern USA. We used age estimates from otoliths and length measurements to calculate growth rates of juvenile river herring (n = 1452). We tested the effects of juvenile river herring densities, zooplankton (biomass and size), habitat area (based on thermocline depth), and water quality (temperature, nutrients, chlorophyll a) on juvenile growth. Mean monthly growth rates ranged from 0.56 to 1.41 mm/d and typically increased throughout the summer. Increased juvenile growth was best predicted by lower juvenile density (β = − 0.104, P < 0.001) and higher zooplankton biomass (β = 0.032, P < 0.05). Combined with information about juvenile densities and mortality, these results broaden the understanding of anadromous juvenile river herring productivity, provide information that can contribute to refining stock assessment and life cycle models, and help to better understand the potential impacts of habitat conservation and restoration decisions.

Brain form (i.e., brain size and morphology) has been linked to variation in foraging behaviour among species of fishes in lakes and oceans, such as larger brains associated with fish foraging higher in the food chain. However, much less is known about these relationships across habitats, or in stream fishes. Therefore, we explore relationships between foraging behaviour and brain form in the omnivorous creek chub (Semotilus atromaculatus) across different streams of Southwest Ontario, Canada. We assessed foraging behaviour variables (i.e., trophic position, proportion of terrestrial energy in diet and foraging flexibility on aquatic and terrestrial resources) against brain form (i.e., relative brain size and the proportional size of the cerebellum, hypothalamus, olfactory bulbs, optic tectum, and telencephalon). Principal component analysis was used to extract covariation patterns among the size of brain regions. We found that creek chub brain size is positively associated with trophic position and proportion of terrestrial energy in diet, but not foraging flexibility. The first principal component, explaining 91% of size covariation among brain regions, was also positively associated with trophic position but not with proportion of terrestrial energy in diet suggesting that brain regions outside of those measured contribute to the association between brain size and proportion of terrestrial energy in diet. Our results suggest that a relationship between brain size and trophic position may be common among fishes, and that foraging on resources from the terrestrial energetic pathway in streams may present a novel, yet to be characterized cognitive challenge for fish.

Manta rays Mobula cf. birostris aggregate off the Atlantic coast of Florida each spring, typically March through May. Eighteen courtship events were documented and four zooplankton samples collected opportunistically during boat-based and aerial surveys in 2021–2024. Eighty-three percent of courtship events involved only two individuals, and four stages courtship (initiation, endurance, evasion, pre-copulation positioning) were observed. Breaching events were observed on every day, except one, that courtship events were documented by boat survey. All zooplankton samples were dominated by copepods with bivalve larvae, chaetognaths, and echinoderm larvae also being abundant. Zooplankton biomass ranged from 23.9 to 39.6 mg m⁻³. These are the first published records of courtship in Mobula cf. birostris, as well as the first insights into its target surface prey. Identifying potential manta ray critical habitat, such as feeding and reproductive areas, especially in data-deficient regions such as the western Atlantic, is a necessary step for conservation.

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.