Environmental Biology of Fishes最新文献

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.

Abstract

Anthropogenic habitat degradation and alien invasive species have led to the rapid decline of freshwater fish biodiversity globally. The knowledge of threatened species’ embryogenesis and larval development could be important for the design of appropriate conservation measures to reverse their decline. Here, we describe the embryonic and larval development of the globally threatened Peloponnese Valencia (Valencia robertae) to inform urgently needed ex situ and in situ conservation initiatives, such as safety stock creation, conservation translocation, and population monitoring. The development of V. robertae is described from the embryonic to the juvenile stage from in vivo imaging, for the first time in detail for this species and genus. Valencia robertae’s fertilised eggs are large (approximately 2 mm), spherical, macrolecithal, translucent, with negative buoyancy, filaments at the outer surface, and several oil globules. They have a long incubation period (approximately 18 days at 20 ± 1 °C) and, in laboratory conditions, a high hatching rate (84%, n = 89). Various types of chromatophores are visible in the embryo, incl. melanophores, xanthophores, and iridophores at the dorsal area of the eye and at the iris. Embryos at hatching measure approximately 5.4 mm SL (6.5 mm TL) and have well-developed caudal and pectoral fins, large eyes, and well-developed mouth; exogenous feeding starts at 24–48 h post hatching. Sequential formation of fins continues with the development of the anal and dorsal fins and is completed by the formation of the pelvic fins, at approximately 11 mm SL (25–30 days post hatching). The ecological and conservation implications of our findings are discussed.

Anadromous salmonid species vary in their use of open ocean, coastal, and inland marine waters. To better understand this diversity in behavior and habitat use, 120 coastal cutthroat trout, Oncorhynchus clarkii clarkii, were caught in southern Puget Sound, Washington, USA, tagged with acoustic transmitters, and 95 were detected by a network of receiver stations. Despite sufficient time to reach other parts of the Salish Sea where many receivers operated, none was detected beyond southern Puget Sound, indicating localized movements. Within southern Puget Sound, fish were detected at 34 of 127 receivers in marine sites throughout the year but especially in spring and fall. Most detection events (between first and last detections at a given receiver) were brief (60.5% were ≤ 2 h and 76.8% ≤ 6 h), indicating movement along the shoreline. However, 823 events (12.8%) exceeded 12 h and 222 (3.4%) exceeded 24 h at a receiver, indicating longer occupancy at certain sites and by certain individuals. The detections also indicated that cutthroat trout were active throughout the 24-h period, but they moved more often at night and less often in other periods than would occur by chance, and they moved more often on ebbing and flooding tides and less often at slack periods. Fish with pressure-sensitive transmitters were almost always (97.3% of records) within 2.5 m of the surface and 76.8% between 1 – 2 m, despite deeper and shallower waters nearby where they could have been detected. The data provide new insights into the behavior of this species, whose marine ecology has not been extensively studied, and differs markedly from the region’s other native salmonids.

The smoothnose wedgefish Rhynchobatus laevis, a shark-like ray classified as Critically Endangered by the International Union for Conservation of Nature, has received limited research attention. To address the knowledge gaps in its spatial behaviour, this study utilised satellite monitoring of a fortuitously captured female over a 51-day period in the Arabian Gulf. Based on the resulting movement track, the individual covered a minimum distance of 712 km, traversing the exclusive economic zones of three different countries. Its track began in the United Arab Emirates, from where it headed north, entering Iranian waters, where it spent most of its time, before continuing westward across the Gulf and eventually reaching Qatari waters. Novel insights into its behaviour revealed an observation of rapid ascents over the study period. Although both diurnal and nocturnal ascents were observed, they occurred predominantly during nocturnal periods. Contrary to the prevailing belief that wedgefish are bottom-associated, the study animal spent a considerable amount of time in the water column. The use of various depths in both nearshore and offshore waters highlights elevated susceptibility to multiple types of fishing gear. This underscores the need for an international cooperative approach to the management and conservation of shark-like rays in the Arabian Gulf.

During elasmobranch ontogeny, increasing body size has been proposed to result in a tradeoff between increased sensitivity and decreased spatial resolution of the electrosensory system, but this hypothesis has not previously been tested. Further, the sensitivity of the electrosensory system has not been examined in any large sharks. In the present study, we examined the behavioral electrosensitivity of large (likely adult) sandbar sharks to prey-simulating electric fields, compared with previously published results for small (juvenile) sandbar sharks. We found that the large sandbar sharks, which were approximately three times larger than the small juveniles previously tested, had lower minimum (0.002 nV/cm) and median (0.5 nV/cm) response thresholds. These represent the lowest sensitivity thresholds of any elasmobranch studied to date. Since electric field detection plays an important role in feeding behavior, increases in sensitivity of the electrosensory system and the corresponding increase in electric field detection distance with growth may be linked to ontogenetic dietary changes.

One of the most conspicuous impacts of dam construction on fish is the blocking of their migratory routes. However, the formation of the reservoir, a lentic environment with distinct hydrological and ecological characteristics, can also constitute an obstacle to migration. This impact, however, is poorly explored in the scientific literature. Therefore, this study aimed to assess the movements of Prochilodus argenteus tagged with radio telemetry transmitters and manually translocated across the Três Marias Dam in the São Francisco River. The Três Marias reservoir covers an area of 1090 km² and ranks among the largest artificial reservoirs in Brazil. Individuals translocated to the Três Marias reservoir showed reduced movement rates and home ranges. They appeared disoriented in the new environment, with many of them settling near fish farms and remaining there throughout the study period. A comparative analysis with existing literature on Neotropical species’ reproductive migration through artificial reservoirs revealed a trend: the ability of migratory fish to navigate reservoirs diminishes with their area, especially those exceeding 50 km² or with a residence time surpassing 30 days. These results indicate that caution is needed when designing fish passage facilities for dams that form larger artificial reservoirs in the Neotropics. Even if these facilities are efficient in attracting and translocating migratory species, behavioral and physiological thresholds may prevent them from reaching suitable areas to complete their reproductive cycle in the new environment formed.