Journal of fish biology最新文献

Siluriform fishes collected from the Rio Negro and Rio Solimões proved to be highly resistant to aquatic hypoxia. In all four species analysed in this study, aquatic oxygen consumption significantly decreased from normoxic levels at water PO₂ values near 1 kPa. Air-breathing activity was observed only in Sturisoma sp. (Rio Negro). In this species, under severe hypoxia, oxygen uptake from the air dominated, but total oxygen uptake was significantly lower than that under normoxic conditions. In Anadoras weddellii (Rio Solimões), aquatic surface respiration was detected. However, the other species (Tympanopleura atronasus and three members of the family of Sternopygidae; Rio Solimões) showed no attempt to supplement aquatic oxygen uptake, even under severe hypoxia. In all species tested, neither ammonia nor urea-N excretion was affected by the decreasing water PO₂. At the lowest water PO₂ levels, the reduction in total oxygen uptake in the face of unchanged nitrogenous waste excretion resulted in extraordinary high nitrogen quotient (NQ) ratios. In normoxia, NQ ratios ranged from 0.16 to 0.34. Urea-N excretion contributed between 19% and 28% to total nitrogen excretion and appeared to be unrelated to natural diet as indicated by the gut length-to-fork length ratio or to plasma urea-N levels. Overall, our data underline the quantitative importance of urea-N for nitrogen excretion in siluriform fishes.

The mummichog Fundulus heteroclitus is a trophically important fish inhabiting Atlantic coastal salt marshes, with few in situ estimates of overwinter survival throughout the species range. We estimated overwinter apparent survival rates of F. heteroclitus at the approximate mid-latitudinal species range [coastal North Carolina (USA)] in four tidal creeks that experience variable winter water temperatures. To estimate apparent survival, we fitted a Cormack-Jolly-Seber model to daily mark-resight data autonomously obtained from fish marked with passive integrated transponder tags. Creek, year, mean daily water temperature, change in mean daily temperature, fish length and fish condition were considered for effects on the modelled parameters: apparent survival (Φ) (product of true survival and site fidelity) and detection probability (p). Modelling showed that water temperature and fish metrics were not related to Φ. Water temperature was directly related to p, indicating reduced fish activity and thus reduced detection probability or poor antenna detection performance at low temperatures. Creek was related to Φ and p, and the creek most open to its downstream estuary (lacking a culvert) had lower rates than the others. Greater loss (fish mortality plus emigration) in this one creek may more effectively transfer production of F. heteroclitus to larger waterbodies via emigration or predation. Conversely, lower Φ may reflect reduced detection efficiency. The results suggest that F. heteroclitus survival is insensitive to variable winter water temperatures typical of thermal dynamics in shallow estuaries in this region of its range. Median creek-specific overwinter Φ rates (range of median values, 2 × 10^-8, 0.04) were roughly equal to previously published rates for these creeks during the growing season (April-October). At these latitudes and with increasingly moderate winters, the results indicate that natural mortality could arise equally or more so from predation during the growing season than mechanisms such as starvation, direct mortality, thermal morbidity and stress-related susceptibility to predation resulting from intermittently low water temperatures during the overwinter season.

Gut microbiota stability is crucial for maintaining fish health. In aquaculture, antibiotics and disinfectants are frequently used to manipulate the host gut microbiota, but the combined effects on asymptomatic fish remain unclear. We investigated the effects of single and combined treatments with antibiotics and disinfectants on grass carp (Ctenopharyngodon idella) gut health, immune response, microbiome dynamics and transcriptome profile. In a 2-week trial, grass carp were exposed to enrofloxacin (10 mg/kg) in the basal diet or povidone-iodine (0.05 mg/L) in fresh water. A 14-day treatment led to significant oxidative stress, as indicated by reduced catalase and total superoxide dismutase activities. Digestive enzyme activities, including amylase and lipase, were also significantly suppressed. Gut microbiota diversity decreased, with notable shifts in dominant bacterial phyla, including reduced abundances of Firmicutes and Bacteroidetes and increased Proteobacteria and Fusobacteria. Transcriptomic analysis revealed downregulation of immune-related pathways, including those linked to IgA production, and suppression of key immune-related genes, such as major histocompatibility complex 2 (MHC2) and tumour necrosis factor alpha (TNF-α). Histopathological analysis showed damaged intestinal villi, increased goblet cell numbers and significant apoptosis in intestinal epithelial cells, as confirmed by terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL) staining and upregulation of caspase-3, caspase-8 and caspase-9. These findings demonstrate that enrofloxacin and povidone-iodine disrupt gut microbiota balance, impair mucosal immunity and induce apoptosis in grass carp.

In April 2022, mass stranding of weedy (common) seadragons occurred, with a total of over 200 individuals washed ashore on beaches in the Sydney, Australia region, recorded by citizens. Causes of the stranding, which is unprecedented, were likely related to a series of east coast low storm events, leading to record wave heights, record coastal rainfall, and potential loss of critical food sources (schooling mysid crustaceans). A significant proportion of the local population was likely lost in this series of events, indicating a future threat to seadragons, with east coast low intensity predicted to increase under human-caused climate change.

The sciaenid white seabass (Atractoscion nobilis) is stocked in California (U.S.) where it supports commercial and recreational marine fisheries. Despite its importance, age and growth remains incompletely understood (e.g., differences between females and males) and has not been validated using known-age fish. In this study, the sectioned sagittal otoliths of 196 hatchery-reared white seabass were analysed. These known-age fish, recaptured after up to 14 years at liberty, allowed reader age interpretation to be validated and reader performance to be quantified. Reader age was not biased relative to true age in hatchery-reared fish, and among-reader precision was high [74.5% agreement, 5.1% average coefficient of variation (ACV)]. Otoliths from wild white seabass were subsequently analysed to develop sex-specific von Bertalanffy growth models, showing that females (age 0-24, n = 355) grow faster and are older than males (age 0-15, n = 381). Otolith morphometric-true age regressions were developed from an expanded dataset of 365 hatchery-reared white seabass to assess an alternative age determination technique for wild conspecifics. Relative to reader age interpretation, age predicted from otolith morphometrics (weight, length, width and thickness) had highly variable agreement (9.5%-68.8%) and ACV (9.5%-44.2%), depending on the age range examined. This study is the first to provide validated, sex-specific age and growth for this moderately long-lived marine fish species, and demonstrates how stocking programmes can serve as an ecological tool to help manage wild populations.

Larval fish are active planktonic predators, with many species feeding initially on copepod nauplii and gradually shifting their selection to copepodites. This study evaluated whether it is possible to develop a general widely applicable empirical model to describe the transition from feeding on copepod nauplii to copepodites in relation to body length, maxilla length and eye diameter. The study also evaluated whether the switch to copepodites is linked to what prey are in the stomach or which copepodite species are replacing nauplii in the diet was also considered. The high degree of covariation among the three morphometric variables makes it difficult to establish statistical differences among predictive models. However, the highest overall fit to a logistic model and accuracy in the transition from nauplii to copepodites are achieved when eye diameter is used as a predictive variable. There are also fewer significant differences in the residuals among fish taxa in the case of eye diameter relative to the other morphometric variables. Fish taxa that shift their diet from copepod nauplii to prey on cyclopoid copepodites demonstrate a slower ontogenetic transition away from nauplii than taxa that shift to calanoid copepodites. Eye diameter may be a stronger predictor of the shift in diet because it contributes to most of the processes that make up the foraging sequence of larval fish prey-predator interactions.

For migratory species, successful navigation is critical to fitness. In Atlantic salmon, for example, there is evidence that during migration from natal streams to the sea, passage through waters with poorly defined or mixed water velocity patterns may constrain directional navigation, causing individuals to become trapped or delayed in lakes or other bodies with slowly flowing water. In this study, we determined the minimum water velocities needed to elicit a behavioural response, in this case a change in the direction of holding position, in both wild origin and domesticated salmon smolts. Smolts required a directional flow in excess of 8.9 cm s^-1 to exhibit effective directional orientation towards the current. Smolts of a domesticated farm origin exhibited a similar qualitative and quantitative response as wild fish. These results suggest that, in areas where the downstream migrating Atlantic salmon smolts pass through low-directional water flow, it may be possible to manipulate directional flows above this minimum threshold, at least temporarily, as a management tool to increase migration success. This is likely to be particularly true where smolts are passing through dams, reservoirs or other impounded waters.

The scalloped hammerhead (Sphyrna lewini) is the shark most frequently landed in Guatemalan artisanal fisheries. From 2017 to 2023, fishery-dependent monitoring recorded 10,000 individuals across three fishing communities. Neonates represented the largest proportion (n = 5860), followed by young of the year (YOY, n = 3929) and significantly fewer juveniles (n = 183) and adults (n = 28). Seasonal patterns were evident, with neonates (84%) and YOY (67.5%) peaking between May and August. The data suggest that neonates and YOY are prevalent seasonally and annually in the three coastal areas.

Hatchery supplementation is frequently employed during the conservation and recovery of imperilled salmon populations. At the smolt stage, hatchery rearing practices often produce individuals that are larger than wild conspecifics. Under this 'bigger is better' strategy, it is assumed that larger fish are less susceptible to predation during migration. We tested this hypothesis on hatchery-reared Atlantic salmon (Salmo salar) smolts with fork lengths representative of those of natural and hatchery origins, allowing us to isolate the influence of size from rearing history. From May to June 2023 we characterized predation risk for acoustic-tagged (n = 50) and tethered (n = 192) smolts of various sizes through a mostly free-flowing section of the Penobscot River, Maine, USA. Across both methods, more than 50% of smolts were predated, with the majority of predation events being attributed to smallmouth bass (Micropterus dolomieu). Tethered smolts of all sizes experienced similar predation risk. In the acoustic telemetry component of this study, smaller, wild-sized smolts incurred greater overall mortality relative to standard hatchery sizes (95% vs. 75%), the majority of which occurred within 3 km of the release site. Collectively, these results allude to a strong predation influence imposed by smallmouth bass on smolts in freshwater sections of the Penobscot River and small-bodied migrants may incur greater predation risk, particularly near stocking sites.

The Amazonian loricariid fish Pterygoplichthys gibbiceps, from the Rio Negro, and Pterygoplichthys pardalis, from the Rio Solimões, are facultative air-breathers that can use the stomach as an air-breathing organ. Measurement of oxygen uptake under progressive aquatic hypoxia revealed a relatively high hypoxia resistance of both species. In both species, air-breathing was initiated at aquatic PO₂ values below 3 kPa. In hypoxia, aerial oxygen uptake was dominant, but in P. gibbiceps total oxygen uptake was reduced to 55 ± 5% of the normoxic values, and in P. pardalis to only 43 ± 4% of the normoxic value. P. pardalis took a greater percentage of its total O₂ consumption from air (92 ± 2%) than did P. gibbiceps (85 ± 3%). Air-breath volume increased with body mass in P. gibbiceps, whereas in P. pardalis air-breathing frequency increased with body mass. The minimal breath volume required to account for aerial oxygen uptake was calculated as 24.9 ± 2.1 mL*kg^-1 for P. pardalis, and 17.3 ± 1.1 mL*kg^-1 for P. gibbiceps. In both species, ammonia and urea-N excretion were not significantly modified under hypoxic conditions, and urea-N excretion contributed a relatively high percentage (23%) to total nitrogen excretion. Measurement of unidirectional and net Na⁺ flux rates during normoxia, hypoxia and subsequent normoxic recovery in P. gibbiceps revealed a significant decrease in Na⁺ influx rate under hypoxic conditions, followed by a significant increase during recovery compared to the control period, with no changes in net Na⁺ balance. The data suggest that a reduction in energy-consuming processes may contribute to the observed hypoxia resistance.