Early Developmental Stages Of Fish Research Articles

Hazardous effects of plastic microfibres from facial masks to aquatic animal health: Insights from zebrafish model

Facial masks are a source of plastic microfibres (PMFs) in the aquatic environment, an emerging risk factor for aquatic organisms. However, little is known concerning its impact during the early developmental stages of fish. Thus, the current study aimed to evaluate the potential interaction and developmental toxicity of PMFs derived from leachate of surgical masks (SC-Msk) and N-95 facial masks (N95-Msk) using a multi-biomarker approach in developing zebrafish (Danio rerio). PMFs from both facial masks were obtained and characterized by multiple techniques. Zebrafish embryos were exposed to environmentally relevant concentrations of PMFs from both facial masks (1000, 10,000, and 100,000 particle L−1), and the toxicity was analysed in terms of mortality, hatching rate, neurotoxicity, cardiotoxicity, morphological changes, reactive oxygen species (ROS) levels, cell viability, and behavioural impairments. The results showed that both facial masks can release PMFs, but the N95-Msk produced a higher concentration of PMFs than SC-Msk. Both PMFs can interact with zebrafish chorion and don't cause effects on embryo mortality and hatching; however, zebrafish embryos showed cardiotoxic effects, and larvae showed increased agitation, average speed, and distance travelled, indicating the behavioural impairments induced by PMFs derived from facial masks. Overall, results showed the risk of PMFs to the health of freshwater fish, indicating the need for greater attention to the disposal and ecotoxicological effects of facial masks on aquatic organisms.

The Impact of Microalgae-Based Diet Enriched Mesocyclopsaspericornis Copepod on the Growth Performance and Biochemical Assessment of Ornamental Fish (Brachydanio rerio)

The cultivation of emerging species in aquaculture and the aquarium industry presents challenges, particularly during the sensitive larval stage, which often has a small mouth. Developing appropriate early feeding protocols is crucial. Copepods have gained recognition as a viable alternative to traditional live fish feeds, as they are natural prey for many fish species and do not necessarily require additional nutritional enrichment. This study aimed to assess the effect of enriching Mesocyclopsaspericornis with different microalgae (Spirulina, Azolla, Chlorella) when fed to Brachydanio rerio, focusing on growth, survival, and biochemical performance of the ornamental fish. Results revealed that Brachydanio rerio exhibited the highest specific growth rate (SGR) when fed with copepods enriched with Spirulina (1.49±0.022), and the highest survival rate was observed when copepods were enriched with Spirulina (93.4±2.549). Further analysis of the biochemical composition of enriched copepods indicated that Chlorella resulted in the highest protein and carbohydrate content, along with lower lipid content compared to other enrichment groups. This suggests that microalgae, particularly Spirulina and Chlorella can serve as a potential feed to enhance the nutritional status of copepods and support the early stages of fish development.

Evaluating the toxicity of estetrol, 17α-ethinylestradiol, and their combination with drospirenone on zebrafish larvae: A behavioural and proteomic study

ObjectiveTo characterise and compare the toxicity of estetrol (E4) and 17α-ethinylestradiol (EE2), and their respective mixture with the progestin drospirenone (DRSP) in zebrafish (Danio rerio) embryos. MethodsZebrafish embryos were exposed to E4, EE2, DRSP, E4+DRSP, and EE2+DRSP in a fish embryo acute toxicity (FET) test. A second test examined behavioural responses and, using label-free proteomics, identified changes in protein expression in response to hormonal treatments, across a range of concentrations, including those that are considered to be environmentally relevant. ResultsIn the FET test, no effects were found from E4 at concentrations ≤100 mg/L, while EE2 induced mortality and morphological abnormalities at concentrations of 1-2 mg/L. In the behavioural test, exposure to 30 ng/L EE2 (∼200 × predicted environmental concentration – PEC) resulted in hypoactivity in fish larvae and exposure to 0.3 ng/L EE2 (∼2 × PEC) led to quantitative changes in protein abundance, revealing potential impacts on RNA processing and protein synthesis machinery. Exposure to E4 did not alter behaviour, but several groups of proteins were modulated, mainly at 710 ng/L (∼200 × PEC), including proteins involved in oxidative phosphorylation. When combined with DRSP, EE2 induced reduced effects on behaviour and proteomic responses, suggesting an antagonistic effect of DRSP. E4+DRSP induced no significant effects on behaviour or proteomic profiles at tested concentrations. ConclusionsThese findings suggest that E4-based combined oral contraceptives present a more favourable environmental profile than EE2-based contraceptives, particularly during the early developmental stages of fish.

Embryogenesis of an aquaculture fish (Dicentrarchus labrax) under simulated altered gravity

Food production and balanced nutrition will be a key challenge for residents of a future base on the Moon or Mars. As a complement to photosynthetic organisms, space aquaculture could provide the range of amino acids required to maintain health. This would rely on shipping fertilized aquaculture fish eggs to the Moon. To determine the feasibility of this, this study sought to test the influence of the conditions of a lunar mission—such as hypergravity during rocket launch and microgravity during the journey—on fish embryos and young larvae. To analyze the potential effects of these gravity changes on the early developmental stages of fish, we conducted two experiments to expose them to: i) 10 min of simulated hypergravity at 5 g (launch duration) and ii) 39 h of simulated microgravity using a random positioning machine. Both experiments used European sea bass (Dicentrarchus labrax) as a model. We analyzed egg oxygen consumption and hatching rates, as well as the expression of genes related to stress and immunity. The results indicated that neither of these altered gravity conditions affected the hatching rate. Simulated microgravity did not impact fish embryo oxygen consumption and appeared to induce faster embryonic development, as the eggs hatched earlier than expected. Levels of glucocorticoid receptors (GR1 and GR2) and heat shock proteins (Hsp90) were not impacted. Only the levels of complement component protein 3 (C3) were significantly higher in simulated microgravity, while interleukin-1β (IL-1β) transcripts were significantly lower in the hypergravity group, compared to controls. This shows that proteins involved in the innate immune system are expressed under altered gravity. Although further experiments are needed, these results suggest that the European sea bass is a promising candidate for space aquaculture.

Zebrafish Injectable Plastic for Identification Tagging (ZIP IT) for larvae to adults using a fluorescent Visible Implant Elastomer

Distinguishing individuals or small groups is essential for many experiments. The regenerative properties of zebrafish make traditional marking methods for rodent models (e.g., tattoos, tissue clipping) ineffective. Fluorescent Visible Implant Elastomer (VIE) can permanently mark juvenile and adult zebrafish but to date no marking technique has been described for larval stage zebrafish. This protocol, Zebrafish Injectable Plastic for Identification Tagging (ZIP IT), utilizes VIE in zebrafish as early as 2 days post fertilization (dpf) using standard microinjection methods and direct injection using an insulin syringe at one month. Larval zebrafish between 2 and 7 dpf were injected in the dorsal musculature. At one month, retention and visibility of the VIE was observed in 72% of the injected fish with no effect on growth; however, a variable change in mortality was observed, generally higher than the uninjected fish. This demonstrates that VIE can be used in very early stages of fish development, providing the first procedure to track individuals or groups within a larger population. Subcutaneous injection of juvenile zebrafish starting at one month has greater than 99%-mark retention and visibility with very low mortality. The combination of larvae and juvenile VIE injections also provide a powerful tool to track and gather data from marked fish throughout their lifespan.•We present a method for tagging individuals or groups of zebrafish at most life stages (larvae or juvenile/adult) with Visible Implant Elastomer (VIE).•The larvae and juvenile injection procedures can be combined so that an individual fish can be tagged for its entire lifetime. Larvae injections become significantly less visible after one month; however, the fish can be reinjected using the juvenile procedure, thus allowing continuity of the visible mark.•This protocol was empirically built on the “Evaluation of VIE tags in Zebrafish (Danio rerio)” by Hohn and Petrie-Hanson (2013) and expanded to include larvae and a small batch elastomer mixing technique.

Effects of temperature shock on the survival of different life stages of large yellow croaker (Larimichthys crocea) by simulated power plant cooling water

Seawater temperatures have increased with global climate change. Coolant water discharged from coastal nuclear power-generating and coal-powered plants, coupled with already increasing seawater temperatures, can adversely affect local fish communities. A sudden drop in temperature caused by the winter shutdown of power plants can also affect fish health and behavior. To assess the effects of temperature change on fish populations, we subjected early life stages of the once commercially important large yellow croaker (Larimichthys crocea) to various water temperature experiments. Fertilized eggs showed the highest hatching rate at 23.4°C and the lowest rate of deformity in hatched larvae at 23.0°C. We determined the incipient lethal temperature for each life stages using derivation models. Ranges between the upper and lower incipient lethal temperatures increased during development from yolk-sac larvae to juveniles, especially in response to cold shock, indicating that later developmental stages in this species are more tolerant of temperature fluctuations. However, thermal tolerance is not solely determined by life stage. Our results suggest that rapid changes in seawater temperature caused by power plant coolant water discharges may significantly affect early developmental stages of fish. Critical thermal maximum tests indicate that the seawater heating rate is significantly negatively correlated with survival time and affects the critical thermal maximum value of L. crocea. On the basis of our determination of incipient lethal temperatures, emergency measures could be taken to avoid adverse economic and ecological impacts due to changes in seawater temperature caused by coolant water discharges.

How much are metals for next-generation clean technologies harmful to aquatic animal health? A study with cobalt and nickel effects in zebrafish (Danio rerio)

Cobalt (Co) and nickel (Ni) are key metals for next-generation clean technologies with broad applications in industrial, military and commercial products. However, the knowledge about their environmental impact and toxicity to aquatic organisms remain limited, especially for the early developmental stages of fish. Thus, the current study aimed to evaluate the developmental toxicity of Co and Ni in zebrafish (Danio rerio). Zebrafish embryo-larval toxicity test (ZELT) was conducted with Co and Ni at different concentrations (10, 20, 40, 60, 80 and 100 mg L−1) during 144 h in a static condition. Multiple biomarker responses were analyzed, such as mortality, hatching rate, neurotoxicity, cardiotoxicity, teratogenesis, and morphometric changes. Results showed high embryotoxicity of Ni compared to Co. Both metals inhibited the hatching process and induced morphological changes, such as inhibition of swim bladder inflation, yolk sac edema and pericardial edema. Co induced bradycardia in zebrafish embryos, while Ni caused tachycardia, indicating differential cardiotoxic effects. Overall, the exposure to Co and Ni disrupts early development of zebrafish, confirming their risk to the health of freshwater fish. Results indicated the ZELT as a suitable approach to assess the environmental risk of metals for next-generation clean technologies.

Investigating mitochondria-immune responses in zebrafish, Danio rerio (Hamilton, 1822): A case study with the herbicide dinoseb

The dinitrophenol herbicide dinoseb is an uncoupler of mitochondrial oxidative phosphorylation (OXPHOS). Studies in fish demonstrate impaired OXPHOS is associated with altered immune system responses and locomotor activity in fish. The objective of this study was to determine the effect of dinoseb on zebrafish (Danio rerio) during early stages of development. We measured oxygen consumption rates of embryos, transcripts related to OXPHOS, growth, and the immune system (cytokines and immune-signaling transcripts), and locomotor activity. We hypothesized that OXPHOS of fish would be impaired in vivo, leading to altered basal immune system expression and locomotor activity. Oxidative respiration assessments in embryos revealed that dinoseb decreased both mean basal respiration and oligomycin-induced ATP-linked respiration. Expression levels of cytochrome c oxidase complex IV, 3-hydroxyacyl-COA dehydrogenase and superoxide dismutase 1 were decreased in larvae following exposure to dinoseb while succinate dehydrogenase complex flavoprotein subunit A, insulin growth factor 1 (igf1) and igf2a mRNA were increased in abundance. Immune-related transcripts chemokine (C-X-C motif) ligand 1 and matrix metallopeptidase 9 (MMP-9) were decreased in expression levels while toll-like receptor 5a and 5b were increased in expression. In addition, a visual motor response test was conducted on both 6 and 7 dpf larvae to determine if dinoseb impaired locomotor activity. Dinoseb decreased locomotor activity in 7 dpf larvae but not 6 dpf. This study improves knowledge of toxicity mechanisms for dinoseb in early stages of fish development and demonstrates that mitochondrial toxicants may disrupt immune signaling in zebrafish.

Amantadine, a promising therapeutic agent against viral encephalopathy and retinopathy.

Outbreaks of viral encephalopathy and retinopathy (VER) in marine and freshwater species severely devastate the aquaculture worldwide. The causative agent of VER is nervous necrosis virus (NNV), which mainly infects the early developmental stages of fish, limiting the effectiveness of vaccines. To counter this case, the anti-NNV potentials of nine drugs with broad-spectrum antiviral activity were explored using ribavirin as a positive drug. Toxicity of the selected drugs to SSN-1 cells and grouper was firstly evaluated to determine the safety concentrations. For screening in vitro, amantadine and oseltamivir phosphate can relieve the cytopathic effects and inhibit NNV replication with the 90% inhibitory concentrations (IC90 ) of 38.74 and 106.75mg/L, respectively. Amantadine has a stronger anti-NNV activity than ribavirin at the with- and post-NNV infection stages, indicating that it is a potential therapeutic agent against VER by acting directly on NNV. Similarly, amantadine also has a strong anti-NNV activity in vivo with the IC90 of 27.91mg/L at the 7days post-infection, while that was 73.25mg/L for ribavirin. Following exposure to amantadine (40mg/L) and ribavirin (100mg/L) for 7days, the survival rates of NNV-infected grouper were increased to 44% and 39%, respectively. The maximum amantadine content (11.88mg/Kg) in grouper brain was reached following exposure for 24hr, and amantadine can be quickly excreted from fish, reducing the risk of drug residue. Results so far indicated that amantadine is a promising therapeutic agent against NNV in aquaculture, providing an effective strategy for VER control at the early developmental stages of fish.

Exposure to acetochlor impairs swim bladder formation, induces heat shock protein expression, and promotes locomotor activity in zebrafish (Danio rerio) larvae

Acetochlor is one of the most widely used herbicides in the world, however, there are few data on the sub-lethal effects of acetochlor on early developmental stages of fish. To address this, we measured survival, deformity, swim bladder formation, embryo oxygen consumption rates, reactive oxygen species (ROS) levels, transcripts (related to swim bladder formation, oxidative damage response, and apoptosis) and behavior responses following exposure to acetochlor (0.001 µM up to 125 µM). Exposure to acetochlor at concentrations 50 µM and above exerted 100% mortality after 3 dpf, and significantly reduced the size of the swim bladder (25 µM). In embryos, basal respiration, oligomycin-induced ATP production, and maximal respiration were decreased 30–60% following a 24 h exposure to 125 μM acetochlor. Acetochlor did not affect ROS levels up to 25 µM in larvae with acute exposure. Acetochlor at 25 µM increased mRNA levels of bax1, hsp70, and hsp90a by ~4-fold in larval zebrafish. In both the visual motor response and light-dark preference test, 25 µM acetochlor increased locomotor activity of larval fish. At lower exposure concentrations, 100 and 1000 nM acetochlor increased the mean time spent in the dark zone, suggesting promotion of anxiolytic behavior. This study presents a comprehensive evaluation of sublethal effects of acetochlor, spanning molecular responses to behavior, which can be used to refine risk assessment decisions for aquatic environments.

Comparative Study of Lipid Content in Leptoclinus maculatus Postlarvae from Kongsfjord and Rjipfjord, Svalbard Archipelago.

A comparative study of lipid profile of the daubed shanny Leptoclinus maculatus postlarvae from fjords of different domains (arctic-boreal Kongsfjord and high-arctic Rjipfjord) of Svalbard Archipelago waters in summer was performed. A more efficient accumulation of lipids in the fishes from Kongsfjord compared to Rjipfjord due to triacylglycerols and wax esters was established. These differences may be related mainly to the trophic conditions of the habitat (species composition, abundance, and availability of food items). The higher level of cholesterol esters than wax esters at the L1 stage of development of the daubed shanny postlarvae compared to older fishes pointed to their active feeding mainly on phytoplankton. The differences in the content of certain classes of phospholipids may indicate adaptive changes at the level of biomembranes, contributing to the maintenance of cell homeostasis in response to abiotic environmental factors, and reflect their additional intake with food at the early stages of fish development.

Bacteriome Structure, Function, and Probiotics in Fish Larviculture: The Good, the Bad, and the Gaps.

Aquaculture is the fastest-growing sector in food production worldwide. For decades, research on animal physiology, nutrition, and behavior established the foundations of best practices in land-based fish rearing and disease control. Current DNA sequencing, bioinformatics, and data science technologies now allow deep investigations of host-associated microbiomes in a tractable fashion. Adequate use of these technologies can illuminate microbiome dynamics and aid the engineering of microbiome-based solutions to disease prevention in an unprecedented manner. This review examines molecular studies of bacterial diversity, function, and host immunitymodulation at early stages of fish development, where microbial infections cause important economic losses. We uncover host colonization and virulence factors within a synthetic assemblage of fish pathogens using high-end comparative genomics and address the use of probiotics and paraprobiotics as applicable disease-prevention strategies in fish larval and juvenile rearing. We finally propose guidelines for future microbiome research of presumed relevance to fish larviculture.

Sub-lethal toxicity assessment of the phenylurea herbicide linuron in developing zebrafish (Danio rerio) embryo/larvae

Due to run-off and rain events, agrochemicals can enter water catchments, exerting endocrine disruption effects and toxicity to aquatic organisms. Linuron is a phenylurea herbicide used to control a wide variety of vegetative weeds in agriculture in addition to residential applications. However, there are few studies that quantify its toxicity to early developmental stages of fish. The objectives of this study were to assess the acute toxicity of linuron to zebrafish embryos/larvae by measuring mortality, morphological deformities, oxidative respiration, gene expression, and locomotor activity via the Visual Motor Response test. Zebrafish embryos at ~6-h post-fertilization (hpf) were exposed to either embryo rearing medium (ERM), or one dose of 0.625, 1.25, 2.5, 5, and 10 μM linuron for up to 7 days post-fertilization (dpf) depending on the assay. Zebrafish larvae exposed to linuron displayed pericardial edema, yolk sac edema, and spinal curvature. Oxidative respiration assessments in embryos using the Agilent XFe24 Flux Analyzer revealed that linuron decreased mean basal respiration and oligomycin-induced ATP-linked respiration in 30 hpf embryos at 20 μM after a 24-hour exposure. In 7 dpf larvae, transcript abundance was determined for 6 transcripts that have a role in oxidative respiration (atp06, cox1, cox4-1, cox5a1, cytb, and nd1); the relative abundance of these transcripts was not altered with linuron treatment. A Visual Motor Response test was conducted on 7 dpf larvae to determine whether linuron (0.625 to 5 μM) impaired locomotor activity. Larval activity in the dark period decreased in a dose dependent manner and there were indications of hypoactivity as low as 1.25 μM. Transcript abundance was thus determined for tyrosine hydroxylase (th1) and glutamic acid decarboxylase 67 (gad1b), two rate limiting enzymes that control the production of dopamine and gamma-aminobutyric acid respectively. The mRNA levels of gad1b (p = 0.019) were reduced with increasing concentrations of linuron while th1 (p = 0.056) showed a similar decreasing trend, suggesting that neurotransmitter biosynthesis may be altered with exposure to linuron. This study improves knowledge related to the toxicity mechanisms for linuron and is the first to demonstrate that this anti-androgenic chemical impairs oxidative respiration and exerts neurotoxic effects associated with neurotransmitter biosynthesis during early development. These data are significant for environmental risk assessment of agrochemicals.

Biomonitoring of Heavy Metal Pollution Using Acanthocephalans Parasite in Ecosystem: An Updated Overview.

Simple SummaryThe environment receives different sources of pollutants, resulting from human industrial pollution as well as activities. This review updates and focuses the light on the relation between the toxicity of heavy metals resulting from bioaccumulation in fish and the parasite bioindication role and its infestation.As a result of the global industrial revolution, contamination of the ecosystem by heavy metals has given rise to one of the most important ecological and organismic problems, particularly human, early developmental stages of fish and animal life. The bioaccumulation of heavy metals in fish tissues can be influenced by several factors, including metal concentration, exposure time, method of metal ingestion and environmental conditions, such as water temperature. Upon recognizing the danger of contamination from heavy metals and the effects on the ecosystem that support life on earth, new ways of monitoring and controlling this pollution, besides the practical ones, had to be found. Diverse living organisms, such as insects, fish, planktons, livestock and bacteria can be used as bioindicators for monitoring the health of the natural ecosystem of the environment. Parasites have attracted intense interest from parasitic ecologists, because of the variety of different ways in which they respond to human activity contamination as prospective indices of environmental quality. Previous studies showed that fish intestinal helminths might consider potential bioindicators for heavy metal contamination in aquatic creatures. In particular, cestodes and acanthocephalans have an increased capacity to accumulate heavy metals, where, for example, metal concentrations in acanthocephalans were several thousand times higher than in host tissues. On the other hand, parasitic infestation in fish could induce significant damage to the physiologic and biochemical processes inside the fish body. It may encourage serious impairment to the physiologic and general health status of fish. Thus, this review aimed to highlight the role of heavy metal accumulation, fish histopathological signs and parasitic infestation in monitoring the ecosystem pollutions and their relationship with each other.

Comparative developmental toxicity of iron oxide nanoparticles and ferric chloride to zebrafish (Danio rerio) after static and semi-static exposure

Iron oxide nanoparticles (IONPs) are used in several medical and environmental applications, but their mechanism of action and hazardous effects to early developmental stages of fish remain unknown. Thus, the present study aimed to assess the developmental toxicity of citrate-functionalized IONPs (γ-Fe2O3 NPs), in comparison with its dissolved counterpart, in zebrafish (Danio rerio) after static and semi-static exposure. Embryos were exposed to environmental concentrations of both iron forms (0.3, 0.6, 1.25, 2.5, 5 and 10 mg L−1) during 144 h, jointly with negative control group. The interaction and distribution of both Fe forms on the external chorion and larvae surface were measured, following by multiple biomarker assessment (mortality, hatching rate, neurotoxicity, cardiotoxicity, morphological alterations and 12 morphometrics parameters). Results showed that IONPs were mainly accumulated on the zebrafish chorion, and in the digestive system and liver of the larvae. Although the IONPs induced low embryotoxicity compared to iron ions in both exposure conditions, these nanomaterials induced sublethal effects, mainly cardiotoxic effects (reduced heartbeat, blood accumulation in the heart and pericardial edema). The semi-static exposure to both iron forms induced high embryotoxicity compared to static exposure, indicating that the nanotoxicity to early developmental stages of fish depends on the exposure system. This is the first study concerning the role of the exposure condition on the developmental toxicity of IONPs on fish species.

Toxic effects of fluridone on early developmental stages of Japanese Medaka (Oryzias latipes)

The herbicide fluridone is intensively applied to control invasive aquatic plants globally, including in the Sacramento and San Joaquin Delta (the Delta), California, USA. Our previous study revealed that the adult stage of Delta Smelt showed acute and sub-lethal adverse effects following 6 h of exposure to environmentally relevant concentrations of fluridone. To further investigate mechanisms of toxicity of fluridone and to assess its toxicity to early life stages of fish, we performed additional exposures using the fish model Japanese Medaka (Oryzias latipes). Male and female Medaka embryos were exposed to concentrations of fluridone for 14 d and showed reduced hatching success in a dose dependent manner. The half maximal effective concentration for the hatching success was 2.3 mg L−1. In addition, male and female Medaka larvae were acute exposed to fluridone for 6 h to assess their swimming behavior and gene expression patterns. Fish exposed to fluridone at 4.2 mg L−1 or higher became lethargic and showed abnormal swimming behavior. The response to the stimuli was significantly impaired by fluridone at 21 mg L−1 and above in males, and at 104 mg L−1 in females. Transcriptome analysis identified a total of 799 genes that were significantly differentially expressed, comprising 555 up-regulated and 244 down-regulated genes in males exposed to 21 mg L−1 of fluridone. The gene set enrichment analysis indicated a number of biological processes altered by fluridone. Among the genes involved in those biological processes, the expression of the genes, acetylcholinesterase, retinoic acid receptor, insulin receptor substrate, glutathione reductase, and glutathione S transferase, exhibited dose- and sex-dependent responses to fluridone. The study indicated that fluridone exposure led to detrimental toxic effects at early developmental stages of fish, by disturbing the biological processes of growth and development, and the nervous system, inducing oxidative stress and endocrine disruption.

Effect of Waveform and Voltage Gradient on the Survival of Electroshocked Steelhead Embryos and Larvae

AbstractElectrofishing is commonly used to monitor fish populations and to control nuisance or invasive fishes. These applications typically focus on juvenile and adult fish, and comparatively less is known about how early developmental stages of fish are affected by electroshock. We examined the survival of hatchery steelhead Oncorhynchus mykiss embryos and larvae exposed to three waveforms often emitted by commercially available electrofishing equipment—AC, square pulsed DC (PDC), and half‐sine‐wave PDC—at different voltage gradients across six developmental stages. There was a strong negative relationship between voltage gradient and survival of steelhead embryos and larvae. Fish were most resistant to electroshock after embryonic pigmentation had occurred (93% mean survival at 4.5 V/cm) until their sensitivity again increased at the swim‐up larval stage (32% mean survival at 2.5 V/cm). The greater survival of embryonic and alevin steelhead exposed to half‐sine‐wave PDC (42% mean survival at a peak voltage gradient of 2.5 V/cm) compared with square PDC and AC (8% mean embryonic survival at 2.5 V/cm) suggested that root mean square voltage gradient is a stronger determinant of mortality than are peak voltage gradient or alternating polarity. The AC waveforms were more deadly to swim‐up larvae than were other waveforms, so the mechanism by which electroshock kills this life stage is probably different than the mechanism that kills steelhead during earlier developmental stages. The results of this study have direct implications to electrofishing in environments where some sympatrically occurring species and developmental stages are not the intended target for electroshock. Accordingly, we offer some simple suggestions for how waveforms can be manipulated to limit, or increase, the mortality of fishes where electrofishing is used as a management or conservation tool.Received December 17, 2015; accepted April 25, 2016 Published online September 8, 2016

Patterns and processes in the drift of early developmental stages of fish in rivers: a review

Current-mediated downstream dispersal by the early developmental stages of fish in rivers is a common phenomenon. Knowledge of patterns and processes in the dispersal, or ‘drift’, of young fishes provides important information on spawning location and spawning success, habitat use, movement paths and flow-ecology relationships more generally, all of which are critical for effective river conservation and management. But despite the importance of such information, our understanding of the patterns and processes of the drift of the early life stages of riverine fishes is limited. Furthermore, riverine fish drift research has tended to occur in isolation from movement studies of other organisms, limiting its integration with higher level concepts and theory. This manuscript reviews the literature on the dispersal of young fishes in running waters. Relevant studies from all climatic zones and geographical regions are investigated, with particular attention given to the types and life history stages of fishes that drift and the seasonal and diel patterns of drifting. We then consider how fish enter the drift and their mode of drifting, attempting to reconcile a long-running discussion, under what we call the ‘active–passive conundrum’. We argue that, aside from eggs, the early stages of fish are not exclusively either passive or active drifters, but usually a mixture of the two, which we term ‘actipassive’ drift. Finally, we evaluate existing knowledge in the context of a general conceptual framework for movement ecology, identifying gaps in our understanding of the roles of internal state, navigation capacity, motion capacity, external factors and internal factors in influencing the dispersal process.

Metabolic characteristics of early life history stages of native marble trout (Salmo marmoratus) and introduced brown trout (Salmo trutta) and their hybrids in the Soča River

AbstractMetabolic potential and respiration rate have been measured in the early life stages of native marble trout Salmo marmoratus (MT), introduced brown trout Salmo trutta (BT) and their hybrids (MH = female of MT × male of BT and BH = female of BT × male of MT) to examine the differences in their metabolic characteristics. Metabolic potential and respiration rate were lowest in each developmental stage in MT, followed by MH, BT and BH. The ratio between metabolic potential and respiration rate (ETS/R) in larvae was also lowest for MT (1.0) and MH (1.1), followed by BT (1.4) and BH (1.6), indicating more intensive exploitation of metabolic potential for actual respiration in MT (100%) and MH (~90%) than in BT (~70%) and BH (~60%). Lower ETS/R means a disadvantage in the case of enhanced metabolic activity due to insufficient enzyme machinery needed for energy production. Thus, potential and actual metabolic activity and ETS/R ratio could account for the different competitive abilities among pure trout species and their hybrids in a particular environment. This is the first report on biochemical and physiological differences between pure MT and their hybrids. The combination of metabolic and respiration rate measurements appears to be a useful tool for estimating the metabolic properties in the early developmental stages of fish.

Biological control of Aeromonas salmonicida infection in juvenile Senegalese sole (Solea senegalensis) with Phage AS-A

One of the major sources of financial loss for the fish farming industry is the occurrence of infections by pathogenic bacteria, especially multidrug-resistant variants. This problem is most prominent during the early stages of fish development and is difficult to address with traditional antibiotic treatment or vaccination. In this way, alternative environmentally-friendly biological strategies to control bacterial infections need to be implemented. Under this scenario, phage therapy appears as a useful and flexible tool for the inactivation of bacterial pathogens in aquaculture. The aim of this study was to test the efficacy of phage therapy to inactivate Aeromonas salmonicida, the causative agent of furunculosis, a fish disease characterized by high mortality and morbidity. In order to achieve this goal, a new phage was isolated, characterized and tested in artificially-infected Solea senegalensis juveniles and in batch bacterial cultures. Results showed that after 6h of treatment the phage inhibited the growth of A. salmonicida both in batch cultures and seawater in the presence of fish juveniles (≈4 and 2.5LogPFUmL−1, respectively). After 72h, fish juveniles treated with phages after exposure to A. salmonicida showed no mortality, contrarily to fishes that were only exposed to the bacterium, which presented a mortality of 36%. This result indicated that phage treatment was effective. In general, a limited regrowth of resistant cells and absence of lysogeny conversion were observed. No significant impact of phage inoculation on natural bacterial communities of aquaculture water was detected. However, the bacterial community associated with fish intestinal tract was moderately affected by the addition of the phage. Interestingly, the differences were not significant when the phage was added in the presence of the host bacteria. Taking this into account, this study provides evidences that the tested phage can be effective and safe against furunculosis during the production of juvenile fish.Statement of relevanceA major source of financial loss for the fish-farming industry is the occurrence of bacterial infections. This problem is most prominent in early stages of fish development, and is difficult to address with antibiotics/vaccination. Alternative environmentally-friendly strategies to control bacterial infections are needed. This study indicates that phages can be effective and safe against furunculosis during fish juvenile production.