Journal of fish biology最新文献

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.

The diet of indicator fish species plays a crucial role in assessing ecosystem health. This study evaluated streams with and without urban influences, focusing on abiotic parameters and the trophic ecology of Psalidodon fasciatus and Piabina argentea. Forested streams exhibited higher redox potential, dissolved oxygen, transparency, and depth, whereas urban streams had higher temperatures, greater widths, and increased levels of total dissolved solids, conductivity, total coliforms, and thermotolerant coliforms. The P. fasciatus population exhibited isometric growth in forested streams and negative allometric growth in urban streams. Conversely, P. argentea exhibited negative allometric growth in both types of environment. The diets of both species included items of autochthonous and allochthonous origin. P. fasciatus had a similar diet in both stream types, whereas P. argentea's diet varied significantly between forested and urban streams. These findings highlight the importance of understanding the interplay between environmental characteristics and species diets, offering crucial insights into the health status of streams, especially those impacted by urbanization.

Anadromous salmonids migrate seaward to exploit feeding and growth opportunities in marine habitats, yet how smolt biological characteristics influence their marine migratory behavior remains poorly understood. This study used 9 years of trout (Salmo trutta) population monitoring data from 15,595 tagged age-0+ parr, 1033 smolts detected migrating downstream in spring, and 99 adults detected returning from their first marine migration to the River Frome (Dorset, UK) to investigate the influence of smolt biological characteristics on their migration timing and maiden marine sojourn duration. Age-specific differences in the influence of smolt length on migration timing were found, with longer 1-year-old smolts emigrating later than their shorter counterparts within the same age class, but the opposite association existed for 2-year-old smolts. A bespoke integrated statistical model quantified the effects of smolt emigration day of year, age, sex, and length on the probability of first-time migrants returning to the river after one or more sea winters. Younger, later migrating smolts had a longer marine sojourn duration than their older, earlier migrating counterparts, and females remained at sea for longer periods than males. Although the statistical model was designed to maximize the use of information available in the data, it revealed only weak effects of smolt biological characteristics on the maiden marine sojourn duration. A complementary simulation study suggested that detecting more spring migrating smolts and analyzing longer time series of trout population monitoring data would increase the ability to detect statistically significant effects. Therefore, a strategic review of the trout population monitoring program, including more long-term biological data collection, is recommended. The modelling work presented here can provide guidance on the size of the required dataset and how to maximize the power of imperfect data.

The tambaqui (Colossoma macropomum, G. Cuvier 1818) thrives both in the ion-poor waters of the Amazon and in commercial aquaculture. In both, environmental conditions can be harsh due to low ion levels, occasional high salt challenges (in aquaculture), low pH, extreme PO₂ levels (hypoxia and hyperoxia), high PCO₂ levels (hypercapnia), high ammonia levels (in aquaculture), and high and low temperatures. Ion transport across the gill is affected by active transport processes, passive diffusive permeability, ion concentrations (the chemical gradient), and transepithelial potential (TEP, the electrical gradient). The latter is a very important indicator of ionoregulatory status but is rarely measured. Using normoxic, normocapnic, ion-poor, low-dissolved organic carbon (DOC) well water (27°C, pH 7.0) as the acclimation and reference condition, we first confirmed that the strongly negative TEP (-22.3 mV inside relative to the external water) is a simple diffusion potential. We then evaluated the effects on TEP of more complex waters from the Rio Negro (strong hyperpolarization) and Rio Solimões (no significant change). Additionally, we have quantified significant effects of acute, realistic changes in environmental conditions-low pH (depolarization), hypercapnia (depolarization), hypoxia (depolarization), hyperoxia (hyperpolarization), elevated NaCl concentrations (depolarization), and elevated NH₄Cl concentrations (depolarization). The TEP responses help explain many of the changes in net Na⁺ flux rates reported in the literature. We have also shown marked effects of temperature on TEP and unidirectional Na⁺ flux rates (hyperpolarization and decreased fluxes at 21°C, depolarization and increased fluxes at 33°C) with no changes in net Na⁺ flux rates. Calculations based on the Nernst equation demonstrate the importance of the TEP changes in maintaining net Na⁺ balance.

Pacific Island communities are heavily dependent on fisheries for subsistence and livelihoods. Yet, despite their importance, coastal fisheries are poorly managed and commercial pressures increasingly threaten them. Groupers (Epinephelidae) are exceptionally vulnerable to overexploitation due to aspects of their biology while their economic value makes them a prime target for commerce. Fiji has a significant grouper fishery and is a useful case study to assess a data-poor, economically valuable sector to evaluate management measures, options, and needs. Data from multiple sources over three decades were integrated with original research involving fisher interviews, market surveys, stock assessments, and underwater census to assess the status of the country's grouper fishery. Catch rates are declining and trade now includes a high percentage of immature groupers, with aggregating species (mainly Epinephelus polyphekadion, Epinephelus fuscoguttatus, Plectropomus areolatus, Plectropomus leopardus) particularly at risk. Estimated annual grouper landings are increasing and now exceed 1000 mt. There is an urgent need to update Fiji's grouper size limits which are grossly inadequate. To build public support and increase awareness, government and nongovernmental organizations should invest in the national 4FJ Fish Smart campaign. Key management recommendations for groupers are (1) improved spatial and temporal protection of spawning aggregations and (2) increased minimum-size restrictions for capture and sale. Findings apply broadly to valuable and vulnerable coastal fin-fisheries in reef ecosystems across many Pacific Island countries and highlight the importance of using multiple data sources and approaches to understand and manage important data-poor fisheries.

The deep-sea demersal fish fauna is characterized by a prevalence of elongated-body forms with long tapering tails. Using baited camera landers at depths of 4500-6300 m in the Pacific Ocean, we observed multiple instances of backward swimming using reverse undulation of the slender body in four species: the cutthroat eel Ilyophis robinsae, abyssal grenadier Coryphaenoides yaquinae, and cusk-eels Bassozetus sp. and Barathrites iris. Backward swimming was used as an escape or repositioning maneuver, reversing for up to seven tail beats before resuming forward swimming in a new direction. The eel I. robinsae reversed with a swimming wave frequency of 0.51-0.95 Hz, wavelength 0.6-0.75 of the body length (L), and large amplitude movements of the head from side to side. C. yaquinae reversed relatively slowly at 0.21-0.52 Hz and wavelength 0.5-0.7 L aided by propulsive movements of the pectoral fins and minimal lateral movement of the head. The ophidiids also used reversed propulsive body waves augmented by paddling with the pectoral fins but with some lateral movement of the head. Pectoral-fin movements in all species were in synchrony with the body movements. The elongated-body form enables backward swimming by reversal of the anguilliform propulsive wave and has the advantage that the fish automatically returns to safety along the path recently traveled. This maneuverability conferred by an elongated body may be a significant factor in selection for body shape in deep-sea fishes.

Understanding the developmental sequence characteristics of the vertebral and appendicular skeletons of the larvae and juveniles of Larimichthys crocea (Naozhou population) can provide theoretical basis for seedling cultivation, environmental adaptation, and taxonomic identification. The cartilage-bone double staining method was used to stain, observe, and analyse the vertebrae, pectoral fins, anal fins, caudal fins, and dorsal fins of the larvae and juveniles of L. crocea (0-30 days post-hatching [DPH]). Results showed that the notochord of the larvae and juveniles of L. crocea was tubular. At 6 DPH, there was obvious segmentation. At 8 DPH, the neural arches began to differentiate, and at 10 DPH, the haemal arches began to differentiate, with complete segmentation of the notochord. At 14 DPH, the dorsal and ventral ribs became clear, and the neural and haemal spines were completely formed by the elongation of the neural and haemal arches, respectively. At 18 DPH, the vertebral bones began to ossify, and ossification was complete at 28 DPH. The median fins of the larvae and juveniles of L. crocea formed in the order of caudal fin, anal fin, and dorsal fin. Among the 800 L. crocea larvae samples, 248 were observed to have skeletal deformities, with a deformity rate of 31.00%. The spine of L. crocea consists of 26 vertebrae, with developmental abnormalities mainly including vertebral anterior convexity, bifurcation of neural spines, vertebral body fusion, and redundancy of neural spines. The above results provide a theoretical basis for enriching the developmental biology of L. crocea.