Journal of fish biology最新文献

Investigating the feeding ecology through the ontogenesis of highly migratory species such as the Pacific Bluefin tuna (PBFT; Thunnus orientalis) is difficult due to its extensive home range and cross-oceanic migration. Here, we show the potential of conducting nitrogen stable isotope (δ¹⁵N) analyses in bulk tissue and amino acids (AAs) in consecutive eye lens laminae of PBFT to reconstruct the trophic life history for an individual tuna. The δ¹⁵N_bulk profiles between individuals caught in the wild and pen-raised were compared. For all individuals, δ¹⁵N_bulk values increased with increasing eye lens diameter or fork length, and exhibited low variation among individual profiles despite tuna being captured in different months. Large δ¹⁵N_bulk shifts (6.8‰-8.5‰) were quantified between the first and last deposited laminae for each individual, suggesting major ontogenetic changes in either foraging areas or trophic position. AA δ¹⁵N values indicate that this highly migratory schooling predator switches feeding areas from lower to higher δ¹⁵N baseline values, reflecting feeding on both sides of the north Pacific, and tends to feed on prey of higher trophic position as it grows. Together, stable isotope analysis in bulk tissue and individual AAs in eye lens laminae could be a powerful approach to investigate changes in the foraging habitat and trophic status of highly migratory species.

Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) are found on both sides of the North Atlantic and often their spawning overlaps in time and space. Yet, haddock has a much more variable recruitment than cod in areas where they are sympatric, a difference that is consistent across ecosystems. At the larval stages, differences in feeding behavior have consequences for growth and survival, potentially contributing to the differences in recruitment between these species. We tested whether haddock displayed different swimming behavior to cod under abundant food conditions, while also comparing their growth every 7 days until 38 days post hatching (dph). Swimming kinematics were quantified from the three-dimensional trajectories of larvae filmed in an aquarium at 11, 21, and 32 dph. Cod swam faster than haddock starting at 21 dph. Differences in swimming speed between species were consistent with body morphology. Haddock was heavier than cod at a given age and body length. At 11 dph, haddock exhibited longer pauses and wider horizontal and vertical turn angles than cod, indicating a moderately larger visual search field compared to cod. Longer pause duration indicates that haddock are searching for prey for longer periods than cod at 11 dph. The differences in prey search disappeared at 21 and 32 dph. The differences in feeding and swimming behavior reported here could play an important role for survival, with consequences for the recruitment of these species.

This research investigated the reproductive timing and spawning dynamics of the European barracuda Sphyraena sphyraena in the Thermaikos Gulf, northern Aegean Sea, where the species is predominantly harvested using gillnets. The study was conducted over 2 years, from May to October, coinciding with the period when the local gillnet fishery targets surmullet Mullus surmuletus. The timing of reproduction was examined by the gonado-somatic index, the macroscopic assessment of the ovarian stage, and the microscopic examination of the ovarian developmental stage. All three indices demonstrated that spawning-capable females were caught in May and June and that spawning ceases by late July to August. Regarding spawning dynamics, the European barracuda is a multiple spawner; the oocyte size frequency distributions of all spawning-capable and actively spawning females were continuous, and postovulatory follicle cohorts from different daily spawning events co-occurred in the ovaries of many of those females. Relative batch fecundity was rounded off to 197 ± 108 oocytes per gram and relative total fecundity at 1263 ± 513 oocytes per gram. The somatic condition increased in postspawning individuals, suggesting a capital breeding reproductive strategy.

Elasmobranch fishes (i.e., sharks, skates, and rays) exhibit remarkable wound-healing capabilities and consistently maintain a high capacity for tissue regeneration throughout their lives. This high capacity for wound healing may be particularly important for neonatal elasmobranchs that are still developing their immune system. However, little is known about the costs associated with wound healing and the potential influence of environmental variables or life history. In this study, we explore (1) the impact of minor, external injuries on the growth and body condition of neonatal blacktip reef (Carcharhinus melanopterus) and sicklefin lemon (Negaprion acutidens) sharks using a long-term fisheries-independent dataset from Moorea, French Polynesia, (2) the influence of ambient temperature on healing rates in neonatal blacktip reef sharks at two experimental temperatures (25°C and 29°C), and (3) variations in umbilical wound-healing rates between blacktip reef and sicklefin lemon sharks using an additional long-term dataset from St. Joseph Atoll, Seychelles. We found no impact of minor, external injuries on growth and body condition in neonatal blacktip reef and sicklefin lemon sharks, accelerated umbilical wound healing in neonatal blacktip reef sharks exposed to elevated ambient temperatures, and distinct umbilical wound-healing rates between neonatal blacktip reef and sicklefin lemon sharks. Enhancing our understanding of sharks' healing capabilities and the influence of environmental factors on this process is crucial for informing handling practices aimed at improving post-release survival rates of captured sharks under current and future oceanic conditions.

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.