Environmental Biology of Fishes最新文献

The population decline of the endangered bitterling species, Acheilognathus typus, following non-native bitterling invasion underscores the need to understand interspecific interactions among bitterling fishes. In this study, the dietary habits of A. typus, alongside introduced non-native bitterling species (Acheilognathus rhombeus and Rhodeus ocellatus ocellatus) and other omnivorous fishes (Oryzias latipes, Pseudorasbora parva, and Rhinogobius sp.), were investigated in a small pond in Japan using gut content and stable isotope analyses (δ¹³C and δ¹⁵N). Analysis revealed that microalgae, particularly diatoms with periphytic or benthic life forms, dominated the gut contents of the three bitterling species, which exhibited high dietary overlaps (Pianka’s index range 0.89–0.98). Although bitterling species displayed similar δ¹³C (mean range −18.4 to −16.1‰) and δ¹⁵N (12.1 to 12.6‰) values, the other omnivorous fishes exhibited distinct isotopic signatures: lower δ¹³C and higher δ¹⁵N values. Isotopic niche overlaps among the three bitterling species were limited (0–2.4%). Furthermore, A. typus and A. rhombeus showed no overlap in the corrected standard ellipse area. These findings suggest that the three bitterling species may forage on similar food items, primarily microalgae, with differing stable isotope ratios, enabling them to partition foraging sites within the confines of a small pond where competition may arise.

Abstract

Fish select habitat based on many abiotic and biotic factors, with some species having narrow habitat requirements due to morphological traits. Fish of the genus Ammodytes (sand lance) are small schooling pelagic forage fish that lack a swim bladder and burrow into sandy substrate when not actively feeding to avoid predation and reduce energy expenditure. Sand lance species in the Pacific and Northeast Atlantic show diel shifts in feeding in the water column and burrowing, but diel patterns for species in the Northwest Atlantic remain unclear. The objectives of this study were to investigate sand lance habitat characteristics and diel behaviour during July–August 2013–2021 on the northeast Newfoundland coast. Integrating underwater camera surveys, sediment grabs, and hydroacoustics, sand lance were found associated with fine sediment (0.5–4 mm) that were < 11˚C (typically ~ 2˚C). Acoustic sand lance biomass in the water column tended to decline between the morning (09:00 Newfoundland Daylight Time, NDT) and late evening (23:00 NDT), while fish densities in sediment grabs peaked during the evening (~ 19:00 NDT) when buried fish more commonly had non-empty stomachs. Findings suggest that sand lance primarily fed in the water column during the day and burrowed in the evening once stomachs were full. Diel patterns were size-dependent, with a higher proportion of larger sand lance (≥ 150 mm) caught in sediments throughout the night, when smaller sand lance (< 150 mm) were absent from sediments. Overall, sand lance species in the Northwest Atlantic appear to exhibit similar habitat requirements and diel patterns to those in other regions.

Lake sturgeon (Acipenser fulvescens), a potamodromous species, have been impacted by habitat fragmentation. Understanding the variation in population structure and spatial distribution in regulated and unimpeded rivers is valuable for recovery or rehabilitation purposes. The objectives of this study were to assess the relative abundance and spatial distribution of lake sturgeon in Rainy River and ascertain demographics of inhabitant juveniles. A standardized, index-netting study was conducted in the Rainy River to target juvenile and adult lake sturgeon. A total of 472 juvenile and 56 adult lake sturgeon were sampled. Juvenile and adult lake sturgeon were found throughout the river; however, juvenile relative abundance was greatest in the lowest river section close to the confluence with Lake of the Woods. Spatial clustering of juveniles and to lesser extent adults was also evident but adults were not necessarily segregated from juveniles. Juvenile annual survival rates were estimated to be approximately 75% and recruitment within this population was detected in all years but was variable in size. There were strong and weak year classes produced; however, they could not be explained by any of the environmental variables assessed.

Abstract

Fishes are relevant indicators of reefs’ conservation status due to the wide variety of functions they perform in the ecosystem. Natural and anthropogenic-induced threats are causing declines in biomass and diversity locally, with immediate effects on trophic structure and ecosystem function. This study evaluated the spatial variation of species richness and the alpha and beta functional diversity of fish assemblages across the Mexican Tropical Pacific (MTP). Visual fish censuses were performed in nine localities between 2012 and 2020. The results showed that species richness and functional diversity of the reef-associated fish assemblage vary at different spatial scales (local and regional), with the highest variability on the local scale. The functional richness and functional divergence presented high values in most localities. On their part, functional beta diversity among regions was low, with almost no functional turnover, while higher trait turnover was observed among localities. This study complements taxonomic diversity metrics by identifying differences due to local conditions, with human intervention as a critical factor. Therefore, it provides information tools that can help improve the management of marine communities subjected to distinct types and degrees of intervention in the MTP.

Skin color aberrations are naturally occurring abnormal pigment patterns that are generally rare among chondrichthyans. In this study, we highlight different skin color aberrations from observations of four shark species native to southern California, USA. We report the first recorded instance of apparent leucism (regional pigmentation loss), in a California horn shark Heterodontus francisci (Girard 1855) and tope shark Galeorhinus galeus (Linnaeus 1758). We also report the apparent second documented occurrence of albinism in the swell shark Cephaloscyllium ventriosum (Garman 1880) from a newly hatched captive individual with parents of normal pigmentation. Lastly, we redescribe a rare secondary color morph in the leopard shark Triakis semifasciata Girard 1855 using previous literature and new sightings/images from sharks in the wild. Color aberrations may lead to different advantages (e.g., certain color morphs may offer additional camouflage) or disadvantages (e.g., reduced pigmentation may limit camouflage and protection from ultraviolet light). Documenting these rare color aberrations augments our understanding of how color patterns can vary between individuals and taxa, and ultimately how these conditions potentially impact shark biology.

Community assembly is influenced by disturbance intensity, sequential colonization (arrival order) of species, and interactions between species arriving early and species arriving later. We documented both intra- and interspecific patterns of colonization following hydrological disturbance using a 20-year time series of marsh-fish density at 21 study sites located in the Everglades, Florida, USA, as a case study of sequential colonization. The critical swimming speed (U_CRIT) of 20 juveniles and 20 adults for six species was estimated using U_CRIT tests to evaluate if U_CRIT predicted timing of re-colonization. We observed a consistent pattern of species colonization over 500 disturbance events. On average, juveniles of early arriving species were collected prior to adults, while adults consistently appeared prior to juveniles for late-arriving species. Density at first collection was inversely correlated with arrival order; early arriving species tended to have higher density when first collected following marsh re-flooding than later arriving ones. Females consistently arrived before males for all species where sex could be identified. Neither absolute nor size-adjusted U_CRIT was correlated with arrival order. Although interspecific colonization was highly repeatable, intraspecific differences among demographic groups were species-specific and possibly tied to reproductive biology and juvenile life history. Juvenile early arrival may indicate rapid colonization of pregnant females (Poeciliidae), diapausing eggs laid before marsh drying, or early development of robust swimming capacity (Cyprinodontidae and Fundulidae); in the Everglades, water currents are absent or too weak to support larval drift as an important mechanism. Stage- and sex-specific U_CRIT and reproductive traits such as embryo diapause in oviparous species need more attention to understand successional dynamics following disturbance in aquatic communities.

The African catfish Clarias gariepinus is a freshwater species native to nearly all of Africa and a small part of Asia. Due to being a generalist species, highly fertile and able to survive in a wide range of environmental conditions, the African catfish has become invasive in many non-native systems where it was introduced, bringing negative impacts to wild ecosystems. In Brazil, C. gariepinus was introduced from Africa for aquaculture in 1986 and established itself in the wild within a decade, after escaping from aquaculture ponds and being further translocated to be used in recreational fishing. As further evidence of the expansion of this invasive species in Brazil, we sequenced the mitochondrial control region and cytochrome b markers to confirm the occurrence of C. gariepinus in a major river in a protected area in the southeastern region, and to assess its genetic diversity. Morphometric data was also collected to aid species identification and to compare to other invasive populations in Brazil. The analysis of 24 specimens revealed a single haplotype for each marker. The single cytochrome b haplotype is identical to a haplotype from the Democratic Republic of the Congo, unveiling the possible genetic origin of the C. gariepinus lineage that invaded Brazil. Morphometric data suggests consistency in the morphometric traits of C. gariepinus invasive populations in Brazil. The assessment and monitoring of the distribution of C. gariepinus in non-native areas are crucial for the maintenance of native freshwater biodiversity and ecosystem functioning worldwide.

Body shape is a morphological attribute that frequently changes as organisms adapt to environmental fluctuations and optimize the use of available resources. In fish whose distribution includes estuarine and riverine environments, it is common to observe changes in body shape that are related to maneuverability and speed of movement in response to temporal and spatial variation in water flow. Here, through geometric morphometric and linear morphometric analysis, the intraspecific morphological variation of the cichlids Amphilophus trimaculatus, Astatheros macracanthus, and Mayaheros beani was evaluated to determine if there are repeated patterns of variation in body shape associated with estuarine and riverine environments. The three species showed the same trend of morphological variation; in the estuaries, the specimens were generally deeper and robust, with a long head and short caudal peduncle, while river specimens had shallowed and fusiform bodies with a short head and long caudal peduncle. The magnitude of the changes was not the same in the three species, as M. beani showed greater differentiation, and some morphological measures showed changes in opposite directions between the species. These findings indicate that the environment occupied by the species is an important factor in the differentiation of body shape, probably due to water flow, although other factors may determine the magnitude and direction of change in some morphological traits.

With rising environmental temperatures causing concern for the status of freshwater fishes, captive breeding programs may become increasingly important for conservation efforts as well as to support fisheries. Although captive broodstocks provide reliable gamete sources for production stocking, prolonged generations under hatchery conditions can result in changes to fishes as they acclimate to captive settings (domestication) — for example, reduced plasticity due to homogenous captive environments. We assessed the effects of rearing temperature and number of generations spent in captivity on the survival and quality (indicated by lack of malformations) of long-term (F_>25) and newly captive (F₁) strains of Ontario hatchery brook trout (Salvelinus fontinalis) with shared genetic history. Elevated temperatures decreased likelihood of survival between the pre-exogenous feed and emergent fry stages and had a greater impact on fry quality (rate of malformations) on F₁ fish compared with F_>25 fish, suggesting no reduction in plasticity due to prolonged captivity. However, overall survival between F₁ and F_>25 fish was not different. The combined effects of elevated rearing temperatures and number of hatchery generations suggest that (selection) changes due to captivity can occur rapidly even under benign conditions and that additive stressor effects of captivity and temperature have the potential to impact newly established strains.

Abstract

We examined sexual dimorphism and parental care in the chocolate gourami (Sphaerichthys osphromenoides) by visual observations, video recording of spawning, and histological analysis of the gonads of individuals in which spawning and mouthbrooding was previously observed. S. osphromenoides is considered a rare exception among labyrinth fishes (Osphronemidae family) because of the presumed maternal parental care, which is not found in other species of this family. According to our observations of 32 spawning events, parental care in this species was always performed by the male. Our visual observations were confirmed by video and histological analysis. This suggests that the sex in this species has probably been misidentified so far. We argue that the putative “females” (previously defined by external features) were in fact males, and that there are probably no exceptions to male parental care in osphronemid fishes.