Fishes, Volume 5, Issue 2 (June 2020) – 9 articles

Stock enhancement is a method for replenishing depleted wild finfish populations by supplementing them with hatchery-raised fish. In Taiwan, silver sea bream (Rhabdosargus sarba) is a predominant commercial species involved in stock enhancement projects. Although management agencies conduct stock enhancement projects, there are a lot of private releases without records. Stock enhancement is performed by the private aquaculture sector without accurate genetic records, potentially leading to unintended consequences for wild populations. We analyzed the genetics of 459 wild and 701 hatchery-reared specimens from nine batches produced by various hatcheries. Wild and hatchery-reared samples could be considered two separate clades by using a set of stable and informative microsatellite markers including type I (from gene introns and 3′UTR) and type II markers (randomly picked up from genome). Type I microsatellite markers could more sensitively reflect the loss of genetic diversity more than type II markers in the domestication process. All specimens were considered native by using mtDNA COI and microsatellites. The genetic composition of the wild population is relatively simple, and the estimated low contribution rate of the hatchery stock (1.3–10.9%; 6–50/459) indicated a weak but significant genetic effect of stock enhancement. Therefore, establishing standards for the stock enhancement of silver sea bream for more effective supplementation of wild populations is imperative. Full article

Invasive predatory lake trout Salvelinus namaycush were discovered in Yellowstone Lake in 1994 and caused a precipitous decrease in abundance of native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri. Suppression efforts (primarily gillnetting) initiated in 1995 did not curtail lake trout population growth or lakewide expansion. An adaptive management strategy was developed in 2010 that specified desired conditions indicative of ecosystem recovery. Population modeling was used to estimate effects of suppression efforts on the lake trout and establish effort benchmarks to achieve negative population growth (λ < 1). Partnerships enhanced funding support, and a scientific review panel provided guidance to increase suppression gillnetting effort to >46,800 100-m net nights; this effort level was achieved in 2012 and led to a reduction in lake trout biomass. Total lake trout biomass declined from 432,017 kg in 2012 to 196,675 kg in 2019, primarily because of a 79% reduction in adults. Total abundance declined from 925,208 in 2012 to 673,983 in 2019 but was highly variable because of recruitment of age-2 fish. Overall, 3.35 million lake trout were killed by suppression efforts from 1995 to 2019. Cutthroat trout abundance remained below target levels, but relative condition increased, large individuals (> 400 mm) became more abundant, and individual weights doubled, probably because of reduced density. Continued actions to suppress lake trout will facilitate further recovery of the cutthroat trout population and integrity of the Yellowstone Lake ecosystem. Full article

Invasive pest species are recognized as one of the important drivers of reduced global biodiversity. In Australia, the 267 invasive plant, animal and microbial species, established since European colonization in the 1770s, have been unequivocally declared the most important threat to species diversity in this country. One invasive pest, the common carp (Cyprinus carpio), has been targeted in an integrated pest management plan that might include cyprinid herpesvirus 3 (CyHV-3) as a potential biocontrol agent. The species-specificity of the released virus (and of field variants that will inevitably arise) has been assessed, and the virus judged to be safe. It has also been hypothesised that, because the virulence of the CyHV-3 will likely decline following release, the virus should be used strategically: initially, the aim would be to markedly reduce numbers of carp in naive populations, and then some other, as yet uncertain, complementary broad-scale control measure would knock-down carp numbers even further. Brief results are included from recent studies on the modelling of release and spread of the virus, the ecological and social concerns associated with virus release, and the restoration benefits that might be expected following carp control. We conclude that, while further work is required (on the virus, the target species, environmental issues, and especially the identification of a suitable broad-scale complementary control measure), optimism must prevail in order to ensure an eventual solution to this important environmental problem. Full article

Abajo: se repite los tres en el resumen. This work studies the effect of high-level fish meal replacement with insect meal: YW meal (obtained from Tenebrio larvae fed a broiler diet), BSF meal (from hermetia larvae fed broilers diet), BSFm meal (obtained from hermetia larvae fed discard fish) on growth performance nutritive indices and in vitro digestibility of Dicentrarchus labrax juvenile. Three different insect meals were used: BSF meal from hermetia larvae fed broilers diet; BSF improve (BSFm) obtained from hermetia larvae fed discarded fish; YW meal obtained from the larvae of Tenebrio fed a broiler diet. Five diets were used, a control (C) diet and four experimental diets by replacing fishmeal with insect meal from BSF at 30% and 50% (BSF30 and BSF50) substitutions, BSFm at 50% substitution (BSF50 m) and YM at 50% substitution (YW50). Nutritional and growth indices worsened by including insect meal, especially for hermetia meal at 50% substitution, BSF50 and BSF50 m. The internal organs’ weight reflected the growth of the fish fed each experimental diet. No differences were found in fillet composition. Nevertheless, under our experimental condition, YW replacement obtained better results than both BSF diets. Full article

In this work the effect of partial or total replacement of fishmeal by plant protein sources and krill and squid meal on growth performance and shelf-life of gilthead sea bream was evaluated. Plant protein dietswith 50 g kg⁻¹ of krill and 100 g kg⁻¹ of squid were supplemented with synthetic amino acidsand at the end of the growing period weight showed no significant differences. The spoilage process of the fish was followed by physicochemical and microbiological measurements together with a colorimetric sensor array (CSA) specially designed for that purpose. The changes in the physicochemical parameters and microbial growth showed that shelf-life of samples were in all cases lower than ninedays. The CSA was not able to show significant differences between both diets, confirming the physicochemical and microbiological results. The fact that the type of feed had no effect on the freshness parameters studied demonstrates that total fishmeal replacement with plant protein blends in the proportions used in this work could be an excellent alternative for feed formulation in aquaculture. Full article

Gut microbiota plays a crucial role in nutrient digestibility and fish health. This study aimed to investigate the effects of alternative feed raw materials on the bacterial communities in the distal intestine and its relationship with nutrient digestibility in yellowtail kingfish (YTK), Seriola lalandi. Two 4-week digestibility trials were conducted to evaluate fish meal (FM), two sources of poultry by-product meal (PBM-1 & PBM-2), blood meal (BLM), faba bean meal (FBM), corn gluten meal (CGM), soy protein concentrate (SPC) and wheat flour (WH). The nutrient digestibility value was determined using the stripping fecal collection method. Bacterial communities were characterized by high-throughput sequencing based on V3-V4 region of the 16S rRNA gene. The most abundant phylum identified in the present study was Proteobacteria. A significant change in the distal intestine was observed in fish fed diets containing CGM and BLM, characterized by a reduction of species richness and diversity. Additionally, significant correlation between nutrient digestibility and intestinal microbiota was observed. Allivibrio, Vibrio, Curvibacter, Ruminococcaceae, and Clostridium were positively correlated, whereas Ralstonia genus was negatively correlated with nutrient digestibility. This study demonstrated that intestinal microbiota could be a useful tool for evaluating the digestibility of feed raw materials; however, further culture-based study is needed to confirm this observation. Full article

Geosmin (GSM) and 2-methylisoborneol (MIB)-induced off-flavors can cause serious problems in a recirculating aquaculture system (RAS), such as delayed harvest and increased production costs, but also damage producers’ reputation. Traditionally, off-flavors have been removed by depuration before harvesting. Rainbow trout (Oncorhynchus mykiss) and European whitefish (Coregonus lavaretus) are commercially valuable species produced for consumers, both being suitable for rearing in RAS. In this study, European whitefish and rainbow trout were raised from juvenile up to 240 g (European whitefish) and 660 g (rainbow trout) to monitor the long-term accumulation of off-flavors. The concentrations in fillet of rainbow trout reached 3.6 ng·g⁻¹ (MIB) and 5.6 ng∙g⁻¹¹ (GSM) with lipid content of 22.5%, while for European whitefish up to 3.2 ng·g⁻¹ (MIB) and 3.9 ng·g⁻¹ (GSM) were found with 14.8% in lipid content. Concentrations up to 58 ng·L⁻¹ (MIB) and 49 ng·L⁻¹ (GSM) were found in the circulating water. Based on the results, the accumulation of MIB proceeds at similar pace for both species. In the case of GSM, the accumulation started similarly for both species but proceeded more quickly for rainbow trout after 140 days of the experiment, with a statistically significant difference (p < 0.05). Full article

Northern pike are an invasive species in southcentral Alaska and have caused the decline and extirpation of salmonids and other native fish populations across the region. Over the last decade, adaptive management of invasive pike populations has included population suppression, eradication, outreach, angler engagement, and research to mitigate damages from pike where feasible. Pike suppression efforts have been focused in open drainages of the northern and western Cook Inlet areas, and eradication efforts have been primarily focused on the Kenai Peninsula and the municipality of Anchorage. Between 2010 and 2020, almost 40,000 pike were removed from southcentral Alaska waters as a result of suppression programs, and pike have been successfully eradicated from over 20 lakes and creeks from the Kenai Peninsula and Anchorage, nearly completing total eradication of pike from known distributions in those areas. Northern pike control actions are tailored to the unique conditions of waters prioritized for their management, and all efforts support the goal of preventing further spread of this invasive aquatic apex predator to vulnerable waters. Full article

The salmon louse (Lepeophtheirus salmonis) causes problems in Atlantic salmon (Salmo salar) aquaculture in the Northern Hemisphere, because infestations can result in both a loss of production and in fish mortality. Several types of treatment have been used to control louse infestations, but these have seen varying success. The aim of this review is to examine the efficacy and safety of commonly used treatments (chemical, biological, mechanical, and preventive measures) as documented in peer-reviewed publications. Efficacy is assessed in relation to a reduction in numbers of lice, and safety is assessed as a lack of negative treatment-associated effects on fish health and welfare (Atlantic salmon and/or cleaner fish). Most chemical treatments showed decreasing efficacy over time, together with the use of increasing concentrations as a result of the development of resistance to the treatments by lice. The need for a restrictive use of pesticides to preserve treatment efficacy has been emphasized. The use of cleaner fish was suggested to be effective, with few or no negative effects towards Atlantic salmon. The use of cleaner fish would be preferable to chemical treatment if the farmed fish health and welfare criteria are met. At present, the number of peer-reviewed publications relating to other forms of treatment and prevention are sparse. Full article