Journal of fish biology最新文献

Traditionally, lethal stomach dissection has been used to study the diets of sharks and rays, but conservation and animal welfare concerns necessitate non-lethal alternatives, such as gastric lavage (stomach or gut flushing). In this study, we summarised gastric lavage studies on elasmobranchs to identify which species/groups it has been effective for, the difficulties encountered and if post-release survival has been evaluated. Secondly, we used a field study to (1) demonstrate how to perform gastric lavage on juvenile rays, (2) assess its effectiveness and (3) verify post-release survival using mark-recapture techniques. Only 23 published studies have used gastric lavage on either sharks or rays, indicating that this technique is still highly underutilised in ecological research. Effectiveness at obtaining stomach contents varied but often exceeded 50%, particularly for rays. Captivity studies provided greater evidence of survival than field studies, and only one field study assessed long-term survival using tag-recapture methods. In this field study, gastric lavage was highly effective for young juvenile rays, and recaptures verified survival for various periods after release. More research is needed to adapt gastric lavage across a wider range of species and sizes, especially larger sharks. Furthermore, incorporating approaches to validate survival following non-lethal handling procedures will be essential to ensure ethical compliance and optimal outcomes for research and conservation.

The stomach-less cunner wrasse (Tautogolabrus adspersus) has been experimentally used as a biological control agent for salmon lice that infest Atlantic salmon (Salmo salar) and to remove biofouling inside sea cages. The cunner demonstrates a strong population structure, suggesting that its diet, and therefore its usefulness for biological control, could differ among its populations along 1086 km of eastern Canada, in response to the biogeography of its prey species. Gastrointestinal tract samples were collected across 14 locations throughout five distinct regions from Southern Nova Scotia to Eastern Newfoundland between 2018 and 2022. Primary constituents of diet, identified using morphology and by percentage weight, were mussels, bryozoans, ascidians, gastropods, unidentified digested material and barnacles. Dietary DNA (dDNA) metabarcoding identified mussels in 46% of guts, amphipods in 45%, bryozoans in 31%, ascidians in 28% and sea anemones in 18%. Sea lice were rare yet present in samples from three separate regions. Permutational multivariate analysis of variance (PERMANOVA) based on DNA metabarcoding suggested that sampling region, location and year all significantly influence diet composition. Regional divergence in diet was greatest between Southwestern Nova Scotia and Northeastern Newfoundland. Invasive cionid ascidians were present almost exclusively in Nova Scotian samples, whereas brittle stars were present almost exclusively in Northeastern Newfoundland samples. dDNA metabarcoding enabled the detection of soft-bodied prey and often identified prey to the species level. Cunner were demersal feeders on neritic sessile or slow-moving benthic animals that comprise the biofouling community. In addition to preying on sea lice and invasive ascidians, we predict that cunner wrasses will reduce the density of biofouling communities on structures used in marine aquaculture.

This study analysed the relationship between body size and the commencement of smoltification in masu salmon Oncorhynchus masou. Juveniles of a strain of O. masou were reared under a simulated natural photoperiod (SNP) and an advanced photoperiod (AP), in which LD15:9 was interrupted by LD9:15 from June to October to induce spring smoltification. Regardless of the photoperiod, the underyearlings were just shorter than 12 cm in fork length (L_F) in October. When the photoperiod in the AP group was switched from short to long days in late October, juvenile O. masou exceeded 12 cm and exhibited increased gill Na⁺/K⁺-ATPase (NKA) activity in December. These changes were accompanied by an increase in circulating levels of insulin-like growth factor (IGF)-1 and IGF-binding protein-2b. In contrast, fish under SNP remained below 12 cm and had low gill NKA activity and hormone/protein levels from October to January. Underyearlings of the same strain reared in a larger tank under a natural photoperiod grew well and exhibited increased gill NKA activity in July when they exceeded 12 cm. These results suggest that an L_F of 12 cm is the threshold size above which juvenile O. masou increase gill NKA activity throughout the year. This implies that they may cease their growth during autumn and winter to avoid exceeding the threshold size required to commence smoltification during spring. Although the threshold size may be related to rearing density or tank size, the findings of the present study suggest that increases in gill NKA activity during summer and the following spring are tightly linked to body size in O. masou.

Co-infection with infectious haematopoietic necrosis virus (IHNV) and Flavobacterium psychrophilum is increasing in prevalence in salmonid aquaculture, and this is accompanied by increased economic losses. The aim of this study was to investigate the synergistic effects of IHNV and F. psychrophilum co-infection on mortality and pathophysiology in masu salmon Oncorhynchus masou. We performed challenge experiments involving co-infection with these pathogens and analysed the proteomic profiles in the kidneys of deceased fish using liquid chromatography tandem mass spectrometry (LC-MS/MS). The onset of co-infectious disease started earlier, and the mortality rate was significantly higher (90%-100%) compared with single infection. Moreover, co-infected fish exhibited severe clinical signs, which were a combination of the clinical signs associated with each single pathogen. Proteomic analysis found that the innate immune response and metabolomic pathways involving pentose-phosphate, fructose and nucleotides were altered in deceased co-infected fish compared with mono-infected fish, and fructose metabolism and the pentose-phosphate cycle were activated in co-infected deceased fish. These findings highlight the need for more comprehensive preventive measures to reduce the risk of multiple pathogen infections and improve the management of co-infectious diseases.

'El Blanquizal' was one of the most important Nassau grouper (Epinephelus striatus) spawning aggregation sites (SAS) in the Mexican Caribbean. However, the characteristics of the population that still uses this site for reproduction remain unknown. The objective of the present study was to monitor and evaluate the Nassau grouper spawning aggregation at El Blanquizal using passive acoustics and visual counts during 2022 and 2023. Based on the sound pattern related to reproductive behaviour (SRRB) and visual monitoring, we determined that the Nassau grouper spawning aggregation season at El Blanquizal occurs from January to March, with up to three reproductive events (one per month). Each event is synchronized with the lunar cycle (the highest reproductive activity occurs between the 9th and 12th days after the full moon), a specific temperature range (26.9-27.7°C) and a particular time of day (28-60 min before sunset). Visual counts estimated an abundance of at least 1700 groupers during the reproductive season, with 80% being adults (TL > 50 cm), reproductive behaviour (courtship) and the identification of colouration phases associated with the spawning event (bicolour phase). These observations confirm that passive acoustics is a highly promising complementary method for monitoring Nassau grouper spawning aggregations and that the El Blanquizal is one of the few sites where Nassau grouper reproduction currently occurs. Its abundance during the spawning aggregation likely places it among the two most important aggregation sites for the species in Mexico, highlighting the priority of continuous monitoring and the implementation of protective measures based on the present results.

This study presents the first record of the non-native species Bryconops aff. melanurus (Bloch 1794) within the upper Paraná River floodplain in Brazil. Two specimens were collected in December 2023 as part of a long-term ecological research programme (PELD). A morphological analysis confirmed species identity. The introduction of B. aff. melanurus into this region raises concerns about its potential impact on the local ichthyofauna because of its dietary plasticity and the disturbed nature of the ecoregion. It is essential to conduct continuous monitoring to assess the ecological implications of the introduction.

Grass carp (Ctenopharyngodon idella) are nonnative, herbivorous freshwater fish that represent an ecological threat in North American waters. However, data are limited on reproductive biology specific to wild populations in midwestern North America, despite recent concern for grass carp establishment within the Great Lakes. Basic information on reproductive traits could be useful to determine reproductive potential, inform future population modelling and provide information to aid control efforts. Our objectives were to evaluate grass carp age-at-maturity, spawning season timing, fecundity type, developmental timing and spawning strategy. Additionally, we evaluated the reliability of the gonadosomatic index (GSI) as a proxy for identifying mature grass carp and compared body condition across study areas. We sampled grass carp in portions of the Mississippi River watershed within the state of Missouri and within the Lake Erie basin. Based on gonad histological samples (n = 274), grass carp are batch spawners with indeterminate fecundity and asynchronous ovarian developmental timing. This allows flexibility in their spawning, exemplified by a protracted spawning season in Lake Erie (April to November) in temperatures ranging from 12.3 to 27.3°C. Minimum observed age-at-maturity for females in Missouri and for both males and females in the Lake Erie population was age-3 and age-2 for males in Missouri. Accuracy of GSI as a measure of maturity during the spawning season was 89.7% and 87.5%, for females and males, respectively. Compared to Missouri, grass carp in Lake Erie had a significantly higher body condition, and females ready to spawn had significantly higher GSI values, suggesting that the grass carp in Lake Erie are healthier and more fecund relative to Missouri and, if left uncontrolled, potentially have a high probability of establishment within the Great Lakes. The results of this study will allow managers to identify the reproductive status of grass carp in the field and more accurately estimate populations and reproductive potential.

The tidal freshwater zone is an aquatic transition zone that links a river to its estuary and provides an important habitat used in the life cycle of resident and migratory fishes. Yet, information on the trophic structure of fishes in this habitat is scarce. To address this gap, we characterize the trophic structure of a fish community in the tidal freshwater zone of the Northwest Miramichi River (New Brunswick, Canada). Stable isotope analyses (δ¹³C, δ¹⁵N, and δ³⁴S) of 17 fish species revealed diverse feeding strategies. Resource use varied across species; some fish relied on either marine or freshwater resources, whereas others integrated resources from both habitats. Fishes varied in their trophic position (range 3.1-4.2) which increased with reliance on marine-derived resources. Species isotopic niche widths varied widely (range 20.4 to 1015.3). Species with intermediate marine resource use (~0.50) had a mix of wide and narrow isotopic niche widths, contrary to wide niches predicted by current literature. Our findings indicate that these narrow-niched species may either act as a sort of tidal freshwater transition zone specialist or assimilate equal proportions of marine and freshwater resources on average. Trophic information from the tidal freshwater zone improves the understanding of fish communities and food web structure where freshwater rivers and marine ecosystems meet.

The large-scale movement behavior of European catfish (Silurus glanis L.) remains poorly understood, despite it being a species of interest for conservation management. We report the movement patterns of 13 native individual catfish, recorded using acoustic telemetry over 160-km estuarine habitat free of migration barriers in the Scheldt River basin (Belgium). The results show that catfish can travel vast distances of over 10 km with a seasonal pattern of fish moving the largest distances in summer. The wels catfish is often considered a relatively sedentary species; however, our results show that this is not the case in systems where they have the freedom to move over large distances. Knowledge about the large-scale movement behavior of the wels catfish can be useful for species conservation, as well as pest control. For instance, the effects of migration barriers could be (re)considered in terms of the large movement distances.