Aquaculture, Fish and Fisheries最新文献

Fisheries studies concerning the related impacts of fishing on the aquatic environment have mostly dealt with industrial fisheries. Concerted large-scale exploitation can lead to stock declines and potentially species extinction. Hydrocynus vittatus is a piscivore and popular recreational fish species that can grow up to 70 cm fork length and weigh up to 15 kg. Hydrocynus vittatus is also a fish of importance in Lake Kariba as local communities along lake shorelines depend on it for both income and food. There is an insufficient understanding of the impacts of artisanal fishing on tigerfish, H. vittatus population parameters and reproductive biology in Lake Kariba. Hence, this study investigated life history traits and population dynamics of H. vittatus in the Ume Basin of Lake Kariba, north-eastern Zimbabwe. Scales were used to estimate the age of tigerfish and the Bertalanffy growth curve used to estimate the growth parameters. A gonadal reproductive stage determination index was used to determine sexual maturity and the logistic growth curve was used to estimate size at 50% sexual maturity (L₅₀). Using the gonadal maturation index, the L₅₀ for males was estimated ranging between 120 and 149 mm. On the other hand, L₅₀ reached between 250 and 299 mm in females. Females had a higher average mean length (335 mm), compared to that of males (289 mm). The length-at-age data from scales had relatively few outliers and moderate scatter. Parameters for the von Bertalanffy growth curve were (L-infinity = 641.5, k = 0.517, t₀ = 3.07). This study highlighted the negative impacts (male-biased sex ratio and small size at maturity) that artisanal gillnet fishing has on the population structure and reproductive potential of tigerfish in the Ume Basin of Lake Kariba. These impacts are a direct result of both legal and illegal fishing activities of the fishers operating in the Ume Basin and based at Musamba Fishing Camp. There is, therefore, an urgent need for the regulatory authority, the Matusadona Conservation Trust, to engage the fishers in developing long-term strategies to reverse the observed unhealthy population status and allow the tigerfish stock to replenish itself.

Investigating the effects of underwater noise on aquatic animals is a research field that is receiving rapidly increasing attention. Despite this, surprisingly few studies have addressed the potential impacts of noise in a marine animal husbandry setting. In this regard, the behaviour of fish in public aquariums can be used as an indicator of well-being, and noise is known to cause behavioural changes. This case study investigates the behaviour of cod (Gadus morhua) and saithe (Pollachius virens) in a large public aquarium when exposed to increased noise levels originating from an aquarium renovation carried out by construction divers. Swimming behaviour, group formation and vertical distribution, along with yawning and scratching frequencies of the fish, were analysed from video recordings made before, during and after the exposure to increased noise levels. The same parameters were also analysed to evaluate potential effects of the presence of divers when not making renovation noise, compared to fish behaviour prior to the renovation. There was a slight change in the depth distribution of both species and a decrease in the number of scratches in cod due to the presence of divers that were not making renovation noise. In the presence of construction noises in the tank, however, both cod and saithe showed a wider array of behavioural changes, including increased swimming speed, changes in depth distribution and increased yawning frequencies. The results from this case study demonstrate that an underwater renovation with increased noise levels impacts fish behaviour and suggests that underwater noise should be considered during the management of aquatic environments, including public aquaria.

Fish aquaculture has become the fastest growing sector in global food production. Thus, ensuring the sustainability of aquaculture practices is of the utmost importance. Studies in higher vertebrates (i.e. mammals) have demonstrated the role of the host microbiome in physiological processes from nutrient acquisition to pathogen protection. Therefore, analysis of fish microbiomes is an important factor to consider with regard to overall animal health and welfare. Rainbow trout (Oncorhynchus mykiss) are an economically valued fish cultured worldwide. Several studies have identified microbial constituents inhabiting the intestinal tract of rainbow trout. To better elucidate some of the core constituents of the rainbow trout intestinal microbiome, this systematic literature review analysed the relative abundance results from 25 articles published on the rainbow trout intestinal microbiome from 2017 to 2021. Bacteria classified within the phyla Firmicutes and Proteobacteria were observed in every study. At the family level, Lactobacillaceae was consistently observed. Additionally, bacteria in the Actinobacteria, Bacteroides, and Tenericutes phyla were identified in at least 50% of the studies. Interestingly, Mycoplasma spp. were occasionally the most dominant organisms present in the microbiome. Overall, the results here identify bacteria that are commonly found members of the rainbow trout intestinal microbiome.

The aim of the present study was to evaluate the water quality, growth performance, body composition, length–weight relationship, condition factors and benefit–cost analysis of giant freshwater prawn (Macrobrachium rosenbergii) cultured with biofloc system in pond conditions. The experiment was conducted in twelve (12) experimental ponds, each measuring 240 m². The control group was cultured without any biofloc (T₁), and biofloc-based three treatments were biofloc with 100% feed (T₂), biofloc with 90% feed (T₃) and biofloc with 80% feed (T₄). The biofloc-based treatments showed significantly higher floc volume, total suspended solids, total heterotrophic bacteria and plankton density than the control (p < 0.05). All the growth parameters were significantly higher in biofloc-based treatments (T₂, T₃ and T₄) than in the control (T₁). The lowest feed conversion ratio was found lowest in T₄ (1.40 ± 0.02) and highest in T₁ (2.13 ± 0.04), which was significantly different among the treatments (p < 0.05). The significantly highest production was obtained 939.02 ± 6.61 kg/ha in T₂, and the lowest was 779.67 ± 7.50 kg/ha in T₁. The length–weight relationship indicated positive allometric growth in all treatments. The condition factor ranged from 0.95 to 1.07, showing that the prawns were in good health throughout all treatments. The results of the present study indicated that M. rosenbergii can adapt to a biofloc-based aquaculture system, and the conventional feeding rations can be reduced up to 20% without affecting the growth and production.

Delta Smelt are thought to be on the precipice of extinction. Studies that examine how this endangered species responds to environmental change are important to informing conservation efforts. In the wild, Delta Smelt are likely to encounter wide variation in the salinity of their environment that is influenced by both natural and anthropogenic factors. We examined how salinity affects the group structure of Delta Smelt across multiple diel cycles. We found that the interaction between salinity (0, 5, 10 and 15 ppt) and time period (Day 1, Night 1, Day 2 and Night 2) influenced their spatial distribution within a group. Specifically, Delta Smelt were less dispersed, more cohesive and more homogenously distributed in saline water than in freshwater, but only on the first day, and this difference was not statistically significant. We also found that Delta Smelt were significantly less dispersed, more cohesive and more homogenous during the day than at night. Thus, Delta Smelt appear to behaviourally adapt to the initial stress of acute salinity exposure, which may mirror their physiological ability to acclimate to such conditions. Additionally, Delta Smelt group structure appears to shift depending on the time of day, suggesting that diel timing may influence conspecific interactions and should be considered in the experimental design of future studies. These findings further our understanding of how Delta Smelt behaviourally respond to environmental and diel variation.

The Italian-native Mediterranean brown trout (Salmo ghigii) is a seriously threatened freshwater fish, especially by anthropogenic hybridisation with the domestic strains of Atlantic origin that have been repeatedly released into the wild for angling. A PCR-restriction fragment length polymorphism (RFLP) assay of the diagnostic lactate dehydrogenase chain-1 (LDH-C1) gene sequences has been routinely applied to distinguish exotic from native brown trout lineages and detect Atlantic introgression signals in the Mediterranean wild populations. Here, we used dermal swab DNA obtained from 28 wild trout to improve laboratory procedures to genetically characterise trout samples at the LDH-C1gene through (1) a capillary electrophoresis analysis of the RFLP fragments and (2) the optimisation of a diagnostic single nucleotide polymorphism analysable through mini-sequencing approaches. The developed methods were fully consistent with those obtained through the traditional approach, but their analytical process is almost entirely automated and digitalised, thus improving result readability and accuracy in the detection of alien introgressed traces in wild Mediterranean brown trout populations.

Increased food demand, reflecting a rising global human population, attaining 8 billion in 2022, has furthered the intensification of farmed aquatic animal production. Intensification practices can be resource demanding for micro and macronutrients, dedicated feeds, fossil fuels, chemotherapeutics, and water. Water replaces evaporative losses and may be used to dilute nutrient-rich wastewater. As an alternative to wastewater discharge, biofloc technology (BFT) uses microbes to manage nutrient levels in production systems. A microbial community grown at high densities can assimilate waste metabolites for growth. This is promoted by increasing the carbon–nitrogen (C:N) ratio using a combination of aquafeed fed to the fish and an additional carbohydrate source, for example, starch, molasses, or bran. The microbial biomass offers a continuous and additional food source to the farmed animal, thus reducing the need for finished aquafeeds and lowering the feed conversion ratio. Although the approach relies on multiple interacting species, BFT can be deployed in relatively low technology settings. This review considers the basis of BFT and identifies areas for innovation and expansion. For example, control of light quantity and quality can influence the biofloc and hence the growth of cultured species. Research on biofloc aquaculture is dominated by studies using tilapia and shrimp, but the technology could be applied to other species, particularly species that are tolerant of biofloc conditions and not highly carnivorous. Biofloc may be a useful biosecurity tool for all or part of the life cycle, and meals made from dried biofloc may enhance the production of cultured species. The key benefits of BFT can potentially be seen in reduced water consumption, lower feed requirements, and improved fish health. This review differs from current review papers in proposing the use of a life cycle assessment in conjunction with BFT, which may be a useful tool for describing and communicating the relative benefits of biofloc systems and their wider environmental impact. This study will serve as a useful knowledge base of BFT information for students, researchers, and stakeholders alike, offering a central source of the main aspects around the culturing of biofloc, key parameters, common species used, areas of potential improvement, and a discussion on where the future of BFT may lie.

Knowledge of species-specific fish biology, ecology, and habitat use is critical for informing science-based management. Yellow perch Perca flavescens are an ecologically and recreationally important fish species. Yet, for many north-temperate systems (e.g. inland lakes of Wisconsin), little is known about yellow perch seasonal habitat use and ecology. We characterised yellow perch seasonal spatial distribution, size–structure, and condition between littoral and pelagic habitats in Crystal Lake (Vilas Co., WI) during the open water period of 2021. Seasonal spatial distribution and population size–structure were characterised by contemporaneous sampling in littoral and pelagic habitats using mini-fyke nets and vertical gill nets, respectively. Relative abundance estimates for yellow perch in the littoral zone were greatest during early spring and declined throughout the open water season. Yellow perch pelagic relative abundance estimates were lowest in spring, peaked at the onset of stratification, and then declined and remained relatively consistent throughout the open water season. In general, yellow perch population size–structure and condition were greatest in the pelagic zone. Our findings suggest that after spring spawning, larger yellow perch prefer/select pelagic habitats, while sub-adults and juveniles prefer/select littoral habitats, potentially resulting from increased predator refugia and(or) resource availability. Our results emphasise the importance of evaluating gear and fishery assessment bias, particularly when the target species may use a range of habitat types within a system.

We evaluated the effect of emptying techniques of a pontoon trap on mortality of Atlantic salmon on their spawning migration along the Finnish coast of the northern Baltic Sea by tagging and releasing fish from commercial trap nets. Two methods currently used, a traditional emptying chute and a lifting bag, were compared. The lifting bag has been developed primarily for minimising injuries for fish during emptying. A custom-built Bayesian system model was used for mortality estimation. We also explored external injuries of salmon and compared the probability of getting an injury between the emptying methods. The mean probability of salmon dying due to release from a trap with an emptying chute was 24% (90% HDI 3%–43%), whereas that for salmon released from a trap with a lifting bag was 13% (90% HDI 1%–24%). Results showed a higher probability of injuries and longer air exposure time in salmon caught with a trap with an emptying chute, which may explain the observed difference in mortality. Manual handling of a lifting bag appears to pose a clear work safety risk for fishers. It is noteworthy that the role of release mortality for northern Baltic salmon stocks is small because the number of salmon released in coastal fishery is currently low.

The once abundant delta smelt Hypomesus transpacificus is now on the verge of extinction. At the UC Davis Fish Conservation and Culture Laboratory, a refuge population has been maintained since 2008 as a safeguard against extinction and to breed and provide fish for research. Due to artificial aquaculture operations, it is assumed that the fish are impacted by life in captivity leading to questions about differences between cultured and captive wild fish. This study looked at the differences in fork length (FL), body weight (BW), fecundity (F) and condition factor (K) of cultured and wild (captive) delta smelt over the last 10 generations (2009–2018) to determine if there were any changes of life-history traits between the two, which may indicate domestication. Results revealed that the cultured population had significantly higher FL, BW, F and K than the wild population. The correlation tests found significant positive relationships between all measured traits except FL and K of wild fish. Significant changes in the measured traits of the cultured population over time were found, whereas none was observed in most wild fish year-classes. This study demonstrated changes of life-history traits in a well-managed fish population over 10 generations in captivity and provides critical information to the coming supplementation plan for the species.