Journal of fish biology最新文献

Preference tests are commonly used to assess fish behavior and cognition in several research fields. This study aimed to investigate how fish perform in a preference test involving extended habituation to the apparatus, which was expected to reduce stress. We contrasted the choice between a sector of the apparatus with natural vegetation, expected to be the preferred stimulus, and a barren sector. Initially, we demonstrated that guppies' preference for the sector with vegetation increased after a 5-day habituation period (Experiment 1). Subsequent experiments systematically modified the testing paradigm to observe effects on the preference. Experiment 2 introduced a physical separation between sectors to facilitate discrete choices, Experiment 3 tested groups of fish, and Experiment 4 used wild guppies. Only the modification in Experiment 3 impacted preference scores: guppies tested in groups showed a higher preference for the vegetation stimulus and spent less time in the central, no-choice sector of the testing apparatus. Overall, this study supports the importance of methodological details in preference tests and highlights the benefits of extended habituation and group testing. Researchers should consider these factors when designing experiments to evaluate cognitive abilities or behavioral preferences in fish. Tailoring testing paradigms to specific research goals can improve the reliability and comparability of results, contributing to a deeper understanding of fish behavior and welfare.

The roundscale spearfish (Tetrapturus georgii) is a poorly studied species with limited information available on its biology, ecology, and population status. Although the adult life stage of the species is morphologically distinguishable from closely related species such as the overexploited white marlin (Kajikia albida), misidentification is common, adding to the uncertainties connected with population assessments of these pelagic highly migratory species. Although genetic studies have recently confirmed its distinction from congeneric species, much of the reproductive biology and population dynamics of T. georgii remain unknown, underscoring the need for further research to guide conservation and management strategies. This study reports the first documented records of an egg and a juvenile T. georgii. Here, we provide photographs, morphological descriptions, and collection site data for genetically confirmed egg and juvenile specimens obtained during two multipurpose research surveys in the Sargasso Sea Subtropical Convergence Zone. These findings contribute new insights into the reproductive biology, early life stages, and ecology of this elusive species.

This study examined the effect of dietary selenium (Se) fortification on growth efficiency, antioxidant status, and liver gene expression in juvenile pangasius catfish. Sodium selenite was incorporated into a basal diet at incremental levels of 0-2.0 mg Se/kg. This resulted in final Se concentrations of 0.63, 0.85, 1.15, 1.68, 2.10, and 2.65 mg Se/kg, respectively. A total of 15 fish, with an average individual weight of 5.6 ± 0.1 g, were subjected to one of six dietary treatments and fed in triplicate over a 60-day period. A significant dose-related enhancement in growth performance was observed, with the optimal dietary Se requirement estimated at 1.75 mg Se/kg. Se-fortified diet significantly increased the activities of digestive enzymes (lipase and protease) as well as antioxidant enzymes, including catalase, glutathione peroxidase, and superoxide dismutase in the liver. Notably, the group fed 1.68 mg Se/kg displayed the highest levels of these enzymes. Additionally, selenium supplementation resulted in an upregulation of the relative expression of insulin-like growth factor 1X1 and 1X2 in the liver, highlighting its pivotal role in growth regulation. Blood parameters showed significant improvements in mean corpuscular hemoglobin and hemoglobin levels with Se supplementation. Proximate analysis showed increasing Se intake resulted in a significant rise in muscle protein content. In pangasius catfish, our results indicate that dietary selenium supplementation can enhance growth efficiency, antioxidant capacity, and hepatic gene expression.

This study investigates the growth and calcification of the appendicular skeleton in Raja asterias (Delaroche, 1809), a member of the Batoidea, to explore the relationship between histomorphology and the mechanics of batoid locomotion within the water column. Although much prior research has focused on the "tessellated pattern" in these fishes, the variable structure of the appendicular skeleton provides fresh insights into the understudied interplay between skeletal histomorphology and the mechanical functions of Batoidea fins. The shape and initial growth of fin cartilage are influenced by the orientation of chondrocyte mitoses prior to mineral deposition, with subsequent calcification playing a pivotal role in shaping skeletal architecture. This study documents two distinct growth patterns: "crustal" and "catenated." The crustal pattern is predominantly observed in larger skeletal elements, such as the central body structures (skull, rostrum, and jaws), girdles, pterygia, and compound radials, whereas fin radials follow the catenated growth pattern. Notably, early-stage chondrichthyan cartilage shares similarities with mammalian metaphyseal growth plate cartilage, though in chondrichthyans, the calcified matrix is not resorbed or replaced by bone. Additionally, a previously unrecognized calcification pattern is identified in the pelvic-fin radials of R. asterias, indicating that the mechanical demands of locomotion in the water column may have driven the evolution of variable fin flexibility in Batoidea. This flexibility is achieved through joint mobility (diarthroses and amphiarthroses), specialized fin structures, and the distinct calcification patterns of the pectoral and pelvic fins.

The lamprologine cichlid genus Telmatochromis was long considered primarily lacustrine and endemic to Lake Tanganyika until an undescribed Telmatochromis species was reported from the Lufubu River (Lake Tanganyika drainage, Zambia). A phylogenomic study in 2021 confirmed the association of Telmatochromis sp. "lufubu" with Telmatochromis along with another riverine species, Neolamprologus devosi (Malagarasi drainage, Tanzania). Here, we quantify the morphological diversity of the genus Telmatochromis and the two associated riverine species using a multivariate dataset combining geometric and classical morphometrics, as well as meristics. We identify three distinct morphological clusters: the "Telmatochromis vittatus complex" with highly elongated bodies and short heads, the "Telmatochromis temporalis complex" with deeper bodies, and the two riverine species with intermediate body elongation and large heads. Further, we formally describe the species endemic to the lower Lufubu River as Telmatochromis salzburgeri sp. nov. and reassign N. devosi to Telmatochromis. Telmatochromis devosi comb. nov. differs from all congeners by the absence of bi- and tricuspid teeth in the inner tooth rows of the oral dentition. T. salzburgeri sp. nov. can be distinguished from all other Telmatochromis species by a prominent orange stripe along the base of the dorsal fin and from T. devosi comb. nov. by the relatively smaller size of the lower pharyngeal jaw. Both riverine species differ from all lacustrine Telmatochromis by a lower number of dorsal-fin spines. Additionally, the riverine species can be distinguished from the T. vittatus complex by having larger heads and longer oral jaws, and from the T. temporalis complex by their lower relative body depth. With the inclusion of new riverine members, the genus Telmatochromis is revealed to be more morphologically and ecologically diverse than previously recognized.

With the expanding global population, interest has increased in the sustainable aquaculture development of indigenous fishes. In Hawai'i, the brassy chub, Kyphosus vaigiensis, has drawn interest as a candidate species for production. However, little is known about its resilience in aquaculture settings where fish are exposed to acute, husbandry-related stressors. To address the response of brassy chub to handling stress, we characterized the effects of simulated netting and confinement stress on physiological parameters indicative of the alarm and resistance phases of the stress response over a 24-h time course. Specifically, we measured plasma osmolality and glucose, mucous cortisol, hepatic activity of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX), and hepatic lipid peroxidation (LPO). Plasma osmolality in stressed fish was increased relative to controls at 1 and 6 h. Mucous cortisol levels were transiently increased in stressed fish at 1 h following handling stress. In stressed fish, plasma glucose was generally increased from 1 h to 24 h relative to controls. By contrast, SOD activity decreased in stressed fish at 6 and 12 h, returning to control levels at 24 h; GPX activity and LPO were unaffected by the handling stressor. The transient and modest responses of mucous cortisol and antioxidant enzyme activity indicate the recovery of brassy chub from handling stress. Moreover, the sustained increase in plasma glucose and lack of change in LPO suggest mobilization of energy and long-term resiliency toward handling stressors.

Due to the logistical and financial challenges in studying migratory marine species, there is relatively limited knowledge of the reproductive biology, behavior, and habitat use of many ecologically important marine megafauna species, including the Atlantic tarpon Megalops atlanticus. Here, we present a novel observation using consumer-grade aerial drones to observe, quantify the scale of, and classify behaviors within a previously unreported tarpon aggregation (N = 182) over the course of a 2-day fish aggregation event. After the event, we analysed and compared observed behaviors (e.g., cruising and clustering) with those of other fish species with well-documented reproductive behaviors, revealing behaviors potentially consistent with courtship, leading us to believe this to be a possible spawning aggregation or aggregation of reproductive/migratory significance. This aggregation occurred in highly altered and urbanized habitat off the coast of South Florida, during the winter, and outside of tarpon's previously reported spring and summer spawning season. Although few studies to date have used drones to monitor teleosts, this study reinforces their potential value as a tool for monitoring fish populations, behavior, and movement.

The spurdog (Squalus acanthias Linnaeus, 1758) is a globally distributed squaliform shark that has historically been overfished but is now recovering in the northeast Atlantic. Data series on spurdog movement and habitat use have been somewhat limited to research surveys due to challenges associated with electronic tagging. Here, we offer a revised attachment method for externally attached pop-up satellite archival tags that was successful in long-term deployments on pregnant females. Twenty-one spurdogs were tagged in two fjord systems in western Norway for an average of 243 days and provided new details about their behaviour, demonstrating affinity for coastal habitat based on the pop-up locations and recovery positions of the tags (84% within 40 km from tagging location), and depth-temperature profiles. It is likely that parturition therefore occurs in these coastal waters, making them important to the life cycle of this species. The realized depth niche of tagged individuals suggested that surveys may miss sharks if they do not cover the full water column because the sharks used large parts of the water column and spent much time in shallower waters, albeit with seasonal variations (deeper and shallower in winter and summer, respectively). Adoption of this tagging method and combination with movement data from acoustic transmitters will help to better resolve the behaviour of this species as it transitions from a species at risk to a managed fishery. Such studies will provide a more comprehensive understanding of the species' habitat requirements that will empower better informed protections against a return to the red list of threatened species.

Fish presence in tailraces is a remarkable management concern in operating hydroelectric power plants (HPP) in Brazilian rivers. Fish get blocked during upstream migration for spawning, and large shoals can last for days in the tailrace; however, the circumstances that attract fish throughout the year to this region are uncertain, especially during drought conditions. To unravel this uncertainty, we modeled the relationship between Pimelodus maculatus abundance and environmental and operational variables (N = 26) in monthly fishing campaigns at the Machadinho HPP (N = 18). A generalized additive model was fitted to fish abundance in which water conductivity, 30-day accumulated precipitation, reservoir inflow, and seasonality explained 93% of the deviance. It was found that abundance decreased as water conductivity increased, but abundance was higher in summer. However, winter showed the highest abundance in the entire rainfall range with peaks between 130 and 150 mm and above 250 mm. An increase in reservoir inflow decreased fish abundance. During droughts, our findings suggest that the powerhouse foundations, particularly the draft tube, may serve as refugia to P. maculatus.

This study investigated the effects of pre-experimental fasting for 2, 7, and 14 days under both unsheltered (12 h dark-12 h light) and sheltered conditions on the critical swimming speed (U_crit) and oxygen consumption (MO₂) of juvenile grass carp, using a modified swim respirometer. Key findings include (1) the U_crit of test fish decreased significantly, by 28%, after fasting for 14 days and sheltering intensified the impact to a 43% decrease, and (2) fish anaerobic capacity decreased after 7 days but increased after 14 days, and was enhanced by sheltering conditions. These findings are important as they indicate that fasting and sheltering can impair grass carp survival and disrupt river ecosystem balance, highlighting the need for habitat conservation.