Journal of fish biology最新文献

Optical characterization of dissolved organic carbon (DOC) freshly collected from the circumneutral "white water" of the Rio Solimoes revealed that it had lower aromaticity, lower molecular weight, and a greater autochthonous content than DOC from the acidic "black water" of the Rio Negro. The tambaqui (Colossoma macropomum), a characid member of the Serrasalmidae, is a model neotropical fish that migrates annually between the two rivers. We analysed ionoregulatory responses of the tambaqui over 24 h in ion-poor water at pH 7.0 and pH 4.0 in the absence and presence of 10 mg L^-1 Rio Solimoes DOC ("SOL DOC"). Measured parameters included transepithelial potential (TEP) across the gills, net flux rates, and plasma concentrations of Na⁺, Cl^-, ammonia, and urea, and branchial Na⁺, K⁺ -ATPase, H⁺, ATPase, and carbonic anhydrase activities. Results were compared to our earlier study using similar protocols to examine the ionoregulatory effects of 10 mg L^-1 DOC ("SGC DOC") collected from black water at São Gabriel da Cachoeira (SGC) in the upper Rio Negro. At pH 7.0, SOL DOC had no effect on the negative TEP across the gills. Exposure to pH 4.0 caused a marked depolarization of the TEP to positive values that was not ameliorated by the presence of SOL DOC. This contrasts with SGC DOC that drove TEP more negative at pH 7.0 and fully protected against the depolarization at pH 4.0. However, SOL DOC promoted positive balance of Na⁺ and Cl^- at pH 7.0 and helped ameliorate the negative balance of these ions seen at pH 4.0. This again contrasts with SGC DOC that exacerbated ion losses at pH 4.0. The protective effects of SOL DOC on ion balance maybe related to increased v-type H⁺ ATPase activity in the gills, and unrelated to TEP. The very different responses to the two DOCs are discussed with respect to their optical properties, the time that they were in storage prior to testing (SOL <1 month, SGC 2 years), and the life history of the tambaqui in the two rivers.

NOD-like receptors are significant contributors to the immune response of fish against different types of pathogen invasion. NOD1 and NOD2 genes of yellow catfish (Tachysurus fulvidraco) were identified and characterized in this study. Yellow catfish NOD1 and NOD2 have open reading frames (ORFs) of 2841 and 2949 bp, encoding 946 and 982 amino acids, respectively. Both NOD1 and NOD2 are intracellular proteins lacking transmembrane regions and signal peptides. Sequence homology analysis revealed that the protein sequences of NOD1 and NOD2 of yellow catfish are highly similar to those of channel catfish. Both NOD1 and NOD2 showed high expression in the head kidney, and spleen. Following challenge with Flavobacterium columnare, NOD1 expression obviously increased in the liver, spleen, midgut, and hindgut, whereas NOD2 clearly increased in head kidney, and gut. Microscopic observation of gill tissues revealed evident epithelial hyperplasia in the secondary gill filaments at 3 and 6 hpi, with a notable decrease in the aspect ratio in comparison with the control group, followed by a return to baseline levels. These findings indicate a potential involvement of NOD1 and NOD2 genes in defense against F. columnare invasion. The findings of this study contribute valuable insights into NOD1 and NOD2's functions in the innate immune response of yellow catfish and other fish species to bacterial infection.

The annual flood pulse is a defining feature of Amazonian floodplain lakes, creating a highly variable environment that influences resource availability, such as food and habitat. These cyclical changes necessitate a high degree of adaptability among fish species, many of which have evolved specialized strategies to cope with the fluctuating conditions. In 2023, the Amazon basin experienced a record-breaking drought event, leading to mass mortality of Amazonian fish and other wildlife. This study examines the effect of this extreme event on fish condition in white-water (Rio Solimões basin) and black-water (Rio Negro basin) floodplain lakes. These contrasting environments provide a unique opportunity to study how different water qualities and extreme water-level fluctuations impact fish condition. Research was conducted during the normal low-water period in November 2019 and the drastically decreased water levels in November 2023. The main objective was to understand how extreme water-level fluctuations affect fish health and nutritional status. A total of 585 fishes were analyzed, with 294 from white-water and 291 from black-water, representing different feeding types to provide a comprehensive picture of changes in fish condition. Water-level changes had a statistically significant impact on fish condition in both areas. Comparing low-water and extreme low-water levels, fish condition was consistently higher during the normal low-water period. The linear mixed-effects model revealed that the intensity of the low-water season had a significant effect on fish length-adjusted mass, suggesting that the decrease in water level is associated with an overall decrease in fish length-adjusted mass. When comparing the mean water-level effect (Glass's Δ) between low-water and extreme low-water levels, we found a bigger effect in the black-water system than in the white-water system. This difference may be attributed to the lower nutrient content and higher levels of humic acids and refractory dissolved organic matter in black-water, which can further limit primary productivity and food availability for fishes.

The European eel (Anguilla anguilla L.) exhibits a remarkable phenotypic plasticity by occupying both marine and freshwater habitats and transitional areas in between. Because these habitats are characterized by different food sources with different fatty acid compositions, it remains unclear how eels from different habitats obtain essential long-chain polyunsaturated fatty acids (LC-PUFAs) to integrate in their lipids. We studied whether the fatty acid composition of eels in three different habitats, that is, a marine lagoon, an estuary, and a river, could be related to the expression levels of genes involved in the LC-PUFA pathways. In general, there were no significant differences in gene expression between eels from marine and freshwater habitats; gene expression in marine and freshwater specimens significantly differed from eels caught in the estuary. However, levels of essential LC-PUFAs and fatty acid ratio markers differed significantly between eels from the river and the marine lagoon. Therefore, we conclude that the LC-PUFA composition of the European eel is likely defined by their food intake from the local environment they are living in and potentially affected by the prevailing conditions, such as food availability, temperature, and salinity.

The urgency of rapid species monitoring is at an all-time high due to the increasing threat of climate change to global ecosystems, in particular freshwater habitats. Fish such as Arctic charr, Salvelinus alpinus, are particularly vulnerable to increasing water temperatures and changes in land use due to their dependence on cold waters and confinement to lacustrine environments. Nonetheless, current monitoring practices, relying on physical capture of organisms, are hindered by resource constraints, desire to manage habitats for recreational fishing, and restricted access to sites. Here we applied a targeted environmental DNA (eDNA) assay in Northwest Scotland to circumvent these limitations and update existing knowledge of Arctic charr habitats, including in locations previously only supported by anecdotal knowledge. Arctic charr eDNA was detected in 10 out of the 16 sites sampled. Additionally, shore and outflow sampling successfully detected Arctic charr eDNA during spawning season, providing a viable sampling strategy where boat access may be limited. These data enabled Arctic charr distribution records to be updated and demonstrated the effectiveness of eDNA as a method for monitoring a vulnerable salmonid in a rapidly changing landscape.

A juvenile spinner shark, Carcharhinus brevipinna, was captured and released in the coastal waters of Rhode Island, USA, where range delineations based on historic records of spinner sharks and the species' congener, the blacktip shark, Carcharhinus limbatus, are plagued by misidentification. The shark in question was within the size range of neonates for C. brevipinna and bore a partially healed umbilical wound. This highlights questions concerning the distribution of nursery habitats for the species along the East Coast of North America and how that may be altered by climate change.

More than 27,000 stomachs from 70 species of fish were collected from the Barents Sea in 2015. Quantitative stomach content expressed relative to the body weight of the predator fish (g g^-1 as %) varied by four to five orders of magnitude for six species with the largest sample size (Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, Greenland halibut Reinhardtius hippoglossoides, long rough dab Hippoglossoides platessoides, polar cod Boreogadus saida, and Atlantic capelin Mallotus villosus). The quantitative stomach contents of individual fish followed a common and strict statistical relationship for predator species or groups of species (by families), and for prey categories across predator species. The common pattern was log-normal-like and was modelled with good fit by different types of right-skewed distributions, that is, variants of the Box-Cox, generalized inverse Gaussian, inverse gamma, or gamma distributions. The long tail in the high end reflects high variation with no clear sign of a plateau, as could be expected from the concept of a "full stomach". This is interpreted to reflect that high stomach contents are rare events that are sampled at low frequencies. The maximum recorded stomach content varied from 1% to 34% of body weight for 55 species of fish, being positively correlated (R² = 0.45) with sample size. About a third of the stomachs were empty, and the low tail of the log-normal-like distribution represents the transition to empty stomachs. The amount of food in the stomachs was overall low compared to maximum values, with mean and median of 2.0% and 1.1%, respectively, for the 17,873 stomachs containing food. Supported by bioenergetic considerations, this suggests relatively low feeding rates of the various fish predators but sufficient to meet their energy demands.

Escape waves in animal groups, such as bird flocks and fish schools, have attracted a lot of attention, as they provide the opportunity to better understand how information can efficiently propagate in moving groups, and how individuals can coordinate their actions under the threat of predators. There is a lack of appropriate experimental protocols to study escape waves in highly social fish, in which the number of individuals initiating the escape and the identity of the initiators are controlled. Indeed, highly social fish or obligate schoolers have a tendency to not respond well or to freeze when tested in experimental setups designed for single individuals. In this manuscript, we report the results of a pilot experiment with limited sample size using an aversive conditioning protocol to trigger a collective escape response to a green light in a group of rummy-nose tetra (Hemigrammus rhodostomus). Our experimental results suggest that aversive conditioning can (i) be successfully used in this schooling species, (ii) trigger collective escape responses, and (iii) be transferred from the training setup to a new environment. We also introduce metrics to characterize learning and forgetting at group level. These results nurture promising future empirical research on the cognitive and behavioral mechanisms of escape responses in schools of fish, both at the individual and collective scales.

A new species of eight-gilled hagfish genus Eptatretus (Myxinidae) is described based on five specimens trawled on the upper continental slope off Kollam, Kerala, India, northern Indian Ocean. Eptatretus gopali sp. nov. can be diagnosed by the presence of eight-gill pouches and gill apertures, 10-11 pre-brachial, 7 branchial, 50-55 trunk, 9-10 tail slime pores, 77-82 total pores, 3/2 multicusp teeth pattern, 40-44 total cusps, absence of nasal-sinus papillae, and a light brown body color. Detailed morphological comparisons with all known eight-gilled species of Eptatretus showed that the new species was distinct from all others by having 40-44 total cusps, characteristic body proportions, and the shortest tail length. E. gopali formed a district clade in the phylogenetic tree and exhibited a genetic distance of 3.6%-11.6% in Cytochrome C oxidase I (COI) sequences and 2.0%-4.9% in 16S rRNA sequences between the congeners. An identification key is also provided for the species of Eptatretus from the Indian Ocean.

Animal growth is a fundamental component of population dynamics, which is closely tied to mortality, fecundity, and maturation. As a result, estimating growth often serves as the basis of population assessments. In fish, analysing growth typically involves fitting a growth model to age-at-length data derived from counting growth rings in calcified structures. Additionally, fish growth can be estimated using length-frequency data or data on changes in length derived from mark-recapture events. In our study of the European grayling (Thymallus thymallus L.) in the alpine region of Germany, we utilized all three types of datasets to develop the initial growth model. For the age-at-length data from scales, we applied the traditional von Bertalanffy growth function using both a Bayesian and a frequentist approach. Furthermore, we adopted the mark-recapture data along with the Fabens model for reparametrizing the von Bertalanffy growth model. The electronic length-frequency analysis (ELEFAN) was employed to examine the length-frequency data of the grayling, encompassing multiple sampling events from 2013 to 2022. Our findings indicated that the mark-recapture data, in conjunction with the Fabens model, yielded the most plausible values for both statistical approaches. When the von Bertalanffy growth function was used, the frequentist approach generated unreasonably high values, whereas the Bayesian version produced meaningful results when appropriate priors were applied, suggesting potential issues with the age-at-length data related to ageing. The ELEFAN approach produced the smallest yet reasonable growth parameters, contradicting other studies on the European grayling. The lower values may be attributed to the lack of larger fish in most of the sampling events, resulting in a relatively low asymptotic length and slow growth rate. As demonstrated in this case study on grayling from the River Inn, the use of growth characteristics may be a currently underestimated yet very useful indicator of target species assessment that can nicely complement other population health indicators.