Fishes, Volume 4, Issue 1 (March 2019) – 22 articles

Environmental enrichment, or the enhancement of an animal’s surroundings when in captivity to maximise its wellbeing, has been increasingly applied to fish species, particularly those used commercially. Laboratory species could also benefit from enrichment, but it is not always clear what constitutes an enriched environment. The zebrafish, Danio rerio, is used widely in research and is one of the most commonly-used laboratory animals. We investigated whether changing the structural complexity of housing tanks altered the behaviour of one strain of zebrafish. Fish were kept in three treatments: (1) very enhanced (VE); (2) mildly enhanced (ME); and (3) control (CT). Level of aggression, fertilisation success, and growth were measured at regular intervals in a subset of fish in each treatment group. The VE fish were more aggressive over time than either ME or CT fish, both in the number of attacks they made against a mirror image and in their tendency to stay close to their reflection rather than avoid it. Furthermore, VE fish were shorter than CT fish by the end of the experiment, though mass was not significantly affected. There was no significant effect of treatment on fertilisation success. These findings suggest that the way in which fish are housed in the laboratory can significantly affect their behaviour, and potentially, their growth. The zebrafish is a shoaling species with a dominance hierarchy, and so may become territorial over objects placed in the tank. The enrichment of laboratory tanks should consider aspects of the species’ behaviour. Full article

Cannibalism occurs in many cultured fish species, especially at the larval and juvenile stages of piscivorous taxa. In farmed percid species, such as pikeperch (Sander lucioperca), intra-cohort cannibalism is a major issue inducing significant losses of the initial stocking density during the first weeks of rearing. Therefore, the present study was designed to investigate the effects of perch larvae (Perca fluviatilis) as live prey on growth, survival and cannibalism in pikeperch larvae under experimental conditions. Additionally, zootechnical and behavioural variables linked to aggressiveness (S postures, attacks, bites and ingestion), and group structures were considered. The survival rate was not different between the two groups (72% with prey vs. 69% without prey), but the cannibalism rate was higher in the group with the prey (28% vs. 10%). The means of final weight and length of pikeperch larvae were higher in the group fed with perch larvae, but size heterogeneity measured by the coefficients of variation for these two parameters did not differ. The specific growth rate was higher in the group fed with perch larvae, but there was no difference between the two groups concerning Fulton’s condition factor. Among all the behavioural variables (aggressiveness, group structure), none differed between the two groups. Full article

Ionic homeostasis is an essential component of functioning cells, and ionic stress imposed by excessive salinity can disrupt cellular and physiological processes. Therefore, increasing salinity of aquatic environments—a consequence of global climate change—has the potential to adversely affect the health of aquatic animals and their ecosystems. The ability to respond adaptively to adverse environmental changes is essential for the survival of species, but animals in early embryonic stages may be particularly vulnerable, as they cannot easily escape from such conditions. Herein, the effects of increasing salinity on the mortality and hatching time of zebrafish (Danio rerio) embryos were investigated. Increasing salinity significantly affected mortality after 24 h of exposure beginning from <2 h post-fertilisation, with 10 parts per thousand (ppt) inducing complete lethality. The 24-h LC50 of NaCl to embryos was estimated to be approximately 5.6 ppt. Interestingly, 5 ppt, a test concentration only slightly lower than the LC50, induced earlier hatching than at lower concentrations. This earlier hatching was also observed even when exposure was commenced at later stages of embryogenesis, despite later-stage embryos not suffering appreciable mortality in response to salinity. The results suggest that earlier hatching is a plastic response which may function to enable embryos to evade unfavourable conditions. Full article

Anisakiasis is fish-borne zoonoses caused by nematodes of the genus Anisakis, contracted by the ingestion of live L3 infective larvae through consumption of raw, undercooked or thermally unprocessed seafood products, such as carpaccio, and white marinated and dry-salted anchovies. In order to maintain the organoleptic properties of the product, the freezing of fish prior to processing is often ignored, especially in households, and traditional processing methods are not sufficient to kill Anisakis larvae. In this study, we investigated the survival and resistance of Anisakis spp. larvae in different processing solutions including varying salt and sugar content, lemon juice, acetic acid, alcohol, wine, and apple vinegar. We also performed a viability test of larvae during processing in anchovy fillets. When exposed directly to different NaCl concentrations, larvae were killed after approximately three days in the strongest (35%) and 10 days in the weakest solution (5%). In lemon juice and lemon juice with added acetic acid, the survival of larvae was around 5 days. In intact alcohol vinegar, larvae were killed under less than 48 h, while in the solution with water their resistance was prolonged to almost 40 days. In fillets, larvae showed increased resistance during carpaccio and white wine vinegar marinades and only dry salting was effective in destroying Anisakis spp. larvae. Full article

In this study, chestnut (Castanea sativa) shell was extracted with different solvents, and immunomodulatory activity was investigated in an in vitro model system using blood and intestinal leukocytes of Oncorhynchus mykiss. Gallic acid (GA) was used as a standard. Chestnut shell extract (CSE) and GA readily entered both blood and intestinal leukocytes. Superoxide anion production and phagocytosis were decreased by low doses of CSE and increased with high doses. CSE and GA differently regulated cytokine expression in blood and intestinal leukocytes. High doses of CSE upregulated IL-1β, TNF-α, and IL-10 in intestinal leukocytes and IL-10 in blood leukocytes. Low doses of CSE upregulated IL-1β and TNF-α in blood leukocytes. GA appeared to be effective only in blood leukocytes. The effects of CSE on pro- and anti-inflammatory cytokines seemed to suggest an alert effect of the immune defense system against a possible infectious agent. The less evident effect of GA in comparison to CSE could have been attributable to the synergistic and/or additive effects of polyphenols in the latter. The immune-stimulating activity of CSE reported here could be useful for future practical applications in fish health. Full article

Trout fishing is one of the primary recreational activities in the southern Appalachians, with large amounts of fish stocked on a regular basis. However, very little is known regarding the fate of hatchery reared carcasses not captured by anglers, representing a likely important ecological resource to local communities. We tested the efficacy of underwater video to characterize short term decomposition and consumption by aquatic scavengers of native brook and non-native rainbow trout, Salvelinus fontinalis and Oncorhychus mykiss. This study took place on the Cherokee Qualla Boundary in North Carolina, a location with one of the highest riverine stocked trout densities in the eastern United States. During May 2017, 10 waterproof cameras were deployed for 1-hour intervals on each carcass twice daily for a period of 5 days. We observed that 75.3% of recorded video contained river chub, Nocomis micropogon, with only 24.7% visited by crayfish, with a maximum of 9 and a mean of 1.93 for N. micropogon. Half of the carcasses were removed within 2 days. Based on natural history evidence and some trail cameras, we believe that otters were removing carcasses. Otters showed no preference for either trout species. Underwater video allowed us to characterize initial decomposition within stream diurnal scavengers in a short period using a visual, non-destructive low-cost method. Future studies should monitor large mammalian scavengers to further elucidate the role of fish stocking on aquatic communities. Full article

‘Wreckfish’ a collective of species belonging to the family Polyprionidae, are an important commercial fishery and have significant aquaculture potential. Until now, genomic or transcriptomic information for any species within the genus Polyprion has either remained unpublished or is non-existent. Using Illumina HiSeq, we compared the transcriptomes of hāpuku (Polyprion oxygeneios) ovaries to explore developmental stage-specific variations underlying their reproductive physiology. We sought to identify differentially expressed genes and the associated shifts in biological pathways between previtellogenic and early vitellogenic ovaries. Ovarian tissue was repeatedly biopsied by gonopore cannulation from the same females (n = 3) throughout oogenesis. Reproductive status of initial biopsies was confirmed as being previtellogenic and that in biopsies collected eight weeks later as early vitellogenic. A de novo hāpuku transcriptome was assembled (146,189 transcripts) from RNA-Seq data without a reference genome. On average, each tissue sample contained 17.5 million trimmed reads. Gene annotation was 80% when using BLASTX against Genbank Non Redundant database. Fifty-three transcripts were differentially expressed within the FDR of 0.05 when previtellogenic and early vitellogenic ovaries were compared; this reduced to 35 differentially expressed genes when transcript duplications were pooled. Among these were genes tentatively associated with the electron transport chain, lipid metabolism, steroidogenesis and mineral/solute transportation. These data provide a snap-shot into stage-specific physiological events during oogenesis in the ovary of a teleost and an extensive molecular resource for research on species in the Genus Polyprion. Full article

Terrestrial protein and lipid sources are commonly used as substitutes for marine fishery-derived raw ingredients in fish diets. However, their use is related with several side-effects on marine fish performance, health, or disease resistance. Physical barriers of the skin, gills, and gut constitute the primary defense mechanism of fish. Skin mucus mucosal mucins, water, proteins, ions, and lipids determine the physical, chemical, and protective characteristics of skin mucus. Very little is known about the influence of diet composition on fish skin mucus fatty acid profile. Gilthead sea bream skin mucus contained 10% of total lipids (TL), which consisted of 50–60% neutral (NL) and 40–50% polar lipids (PL) fractions. Σn−3 long chain polyunsaturated fatty acids (LC-PUFA) deposition was preferential in the NL fraction, whereas Σn−6LC-PUFA accumulation was similar in both lipid classes. Docosahexaenoic acid (DHA; 22:6n−3) was the main LC-PUFA stored in skin mucus (14% TL) in relation to eicosapentaenoic acid (EPA; 20:5n−3) (2–3% TL) and arachidonic acid (ARA; 20:4n−6) (2% TL). This study denotes the importance of DHA as component of skin mucus lipids compared to other essential fatty acids, such as EPA and ARA, as well as importance of maintaining an adequate Σn−3/ Σn−6 ratio, regardless of dietary intake. Full article

Four different wreckfish (Polyprion americanus) broodstock batches were maintained in research facilities under different photo and thermo-period conditions, one in Greece, the Helenic Center for Marine Research (HCMR, n = 3) and three in Spain: Instituto Español de Oceanografía (IEO, n = 13) in Vigo, Aquarium Finisterrae (MC2, n = 21) in A Coruña and Consellería do Mar (CMRM, n = 11). The CMRM includes two centers that work together: Instituto Galego de Formación en Acuicultura (IGAFA) and Centro de Investigacións Mariñas (CIMA), both in Pontevedra. During the five years of the project DIVERSIFY (Exploring the biological and socio-economic potential of new-emerging candidate fish species for the expansion of the European aquaculture industry, 2013–2018) works focused on the reproductive biology of the species, broodstock, and larvae nutrition and development of incubation and larval rearing protocols have been carried out. In terms of reproduction, catch methods of new wild animals, the reproductive cycle, sperm characteristics evaluation, and spontaneous and induced spawning methods have been described for wreckfish. Regarding nutrition, the positive effect of two types of enrichment on the fatty acid profiles of Artemia and rotifer has been verified. The relationship between the fatty acid profile of the diets supplied to the broodstock and the fatty acid profile obtained in the oocytes and eggs of the females fed with different diets, has also been demonstrated. Finally, early larval ontogeny has been described and incubation and larval rearing protocols have been proposed based on the results obtained in the different experiments of temperature, growth, survival, and larval feeding that were carried out. Full article

Anisakidosis is a fish-borne zoonosis caused by parasitic nematodes of the family Anisakidae, of which the species belonging to Anisakis simplex complex are the most representative. It is considered an emerging disease in Spain. The objective of this study is to analyse the presence of larvae in fish frequently consumed in Spanish supermarkets, inferring the risk of infection. In total 1,786 specimens of 9 different fish species, from two geographical origins (Atlantic and Mediterranean), acquired fresh and not eviscerated were examined for anisakid nematodes. Analysis showed that 33.7% of the samples were parasitized by Anisakis larvae. The horse mackerel (Trachurus trachurus) presented the highest total prevalence (66.0%), followed by the silver hake (Merluccius bilinearis) (59.5%), the mackerel (Scomber scombrus) (58.4%), the blue whiting (Micromesistius poutassou) (53.9%) and the European hake (Merlucius merlucius) (45.0%). In general, the prevalence was higher in Atlantic than in Mediterranean fish. In all the species analysed, a higher presence of the parasite was detected in the viscera than in the flesh, although in the most parasitized species a noteworthy prevalence and abundance was observed in the flesh. In conclusion, risk factors, like fish species and origin, should be considered by consumers, in addition of following the recommendations established by Commission Regulation (EU) No1276/2011 and the Spanish Royal Decree 1420/2006. Full article

For farmers of new fish species, market adoption is needed in order to grow a viable business. Farmers may try to sell the new species in their firms’ domestic markets, but they might also look at other markets. However, as markets are becoming more global and competitors more international, considering internationalization may be a necessity rather than a choice. Using diffusion modelling, and based on results of an online supermarket experiment, the innovation and imitation parameters are estimated and diffusion curves for five countries predicted in an attempt to determine the best lead market for introducing fillets of farmed greater amberjack (Seriola dumerili). The production capacity consequences of implementing different internationalization strategies (i.e. “sprinkler” and “waterfall”) were also explored. A waterfall strategy refers to the sequential introduction of a product in different markets, whereas the sprinkler strategy concerns the simultaneous introduction of a product in multiple international markets. Since a sprinkler approach requires many resources and the ability to quickly ramp up production capacity, a waterfall approach appears more suitable for farmers of greater amberjack. Italy and Spain appear to be the best lead markets for greater amberjack farmers to enter first. Full article

Among the many anthropogenic chemicals that end up in the aquatic ecosystem, heavy metals, in particular cadmium, are hazardous compounds that have been shown to affect developmental, reproductive, hepatic, hematological, and immunological functions in teleost fish. There is also evidence that cadmium disturbs bone formation and skeletal development, but data is scarce. In this work, zebrafish was used to further characterize the anti-osteogenic/osteotoxic effects of cadmium and gain insights into underlying mechanisms. Upon exposure to cadmium, a reduction of the opercular bone growth was observed in 6-days post-fertilization (dpf) larvae and an increase in the incidence of skeletal deformities was evidenced in 20-dpf post-larvae. The extent and stiffness of newly formed bone was also affected in adult zebrafish exposed to cadmium while regenerating their caudal fin. A pathway reporter assay revealed a possible role of the MTF-1 and cAMP/PKA signaling pathways in mechanisms of cadmium osteotoxicity, while the expression of genes involved in osteoblast differentiation and matrix production was strongly reduced in cadmium-exposed post-larvae. This work not only confirmed cadmium anti-osteogenic activity and identified targeted pathways and genes, but it also suggested that cadmium may affect biomechanical properties of bone. Full article

Skipjack tuna is targeted by various types of fishing gear in coastal countries. Due to its resilience, it has withstood heavy fishing pressure in the past few decades. Coastal drifting gillnet fleets also mark skipjack as their main target, but it is often overlooked in terms of stock assessment. This study provides new information on an abundance index based on fishery-dependent data from 2010 to 2017. Generalized linear models (GLMs) were used to standardize the catch-per-unit-of-effort (CPUE) using year, quarter, and gross tonnage as the prediction variables. Model goodness-of-fit and model selection were based on the Akaike Information Criterion (AIC), the pseudo coefficient of determination (R²), and model diagnostics with a residual analysis. The final estimation of the abundance index was calculated by least square means or marginal means. The results showed that the index was heavily influenced by the year and quarter, but it did not relate to the vessel’s capacity. While the CPUE series fluctuated greatly, it showed a declining trend over the years of observation. Full article

Global consumption of seafood is steadily increasing, as is the variety of seafood, including dishes with raw or undercooked fish, leading to an increased risk of seafood-borne parasitic diseases. To address today’s challenges to understand the biology and ecology of these parasites in an ever-changing environment and to tackle their pathogenicity, multidisciplinary research is needed. In addition, the gap between research and stakeholders must be bridged to decrease the risk these parasites pose to public health. A “One-Health” approach to research is necessary to ensure that consumers, aquatic animals, and environmental health questions are assessed in an integrated and holistic manner, resulting in a more comprehensive understanding of the issues associated with seafood-borne parasitic diseases and potential solutions. However, when it comes to seafood-borne parasitic diseases, there is limited guidance available for a “One-Health” approach since these diseases can be less known. In this article, the focus is on parasitic diseases caused by seafood, which have been less studied even in some developed countries where seafood is popular. A brief overview of some of the seafood-borne parasitic diseases is provided followed by the significance of the awareness among various stakeholders in a country. In this article, it is argued that researchers and stakeholders are closely connected and a knowledge gap in one can result in a gap in knowledge and awareness in the other, causing an inability to accurately estimate the issues caused by these parasites. It is suggested that raising awareness, supporting research and training of all stakeholders are crucial for the prevention of seafood-borne parasitic diseases and the protection of the health of seafood consumers. Full article

The ability to assess welfare is an important refinement that will ensure the good condition of animals used in experimentation. The present study investigated the impact of invasive procedures on the patterns of movement of zebrafish (Danio rerio). Recordings were made before and after fin clipping, PIT tagging and a standard pain test and these were compared with control and sham handled zebrafish. The fractal dimension (FD) from the 3D trajectories was calculated to determine the effect of these treatments on the complexity of movement patterns. While the FD of zebrafish trajectories did not differ over time in either the control or sham group, the FDs of the treatment groups reduced in complexity. The FD of fish injected with different strengths of acetic acid declined in a dose-dependent manner allowing us to develop an arbitrary scale of severity of the treatments. The 3D trajectory plots from some groups indicated the presence of repetitive swimming patterns akin to stereotypical movements. When administered with lidocaine, which has analgesic properties, the movement complexity of fin clipped fish reverted to a pattern that resembled that of control fish. Fractal analysis of zebrafish locomotion could potentially be adopted as a tool for fish welfare assessment. Full article

Coastal predatory fish are of key importance for the provisioning of ecosystem services in the Baltic Sea. Worldwide, however, there has been a general and sharp decline in predatory fish populations, in turn threatening the viability and function of marine ecosystems. On the basis of the literature, the past (data until the 2000s) and current (data until early and mid 2010s) trends in abundance of coastal predatory fish in the Baltic Sea are reviewed in this paper. Potentially important impacting factors behind the temporal development of the populations and measures to strengthen and restore them are also discussed. Available data from coastal fish monitoring programs suggest a stable or increasing abundance of coastal predatory fish as a functional group and for the species perch in the majority of areas assessed in the Baltic Sea. For pike and pikeperch, data to support assessments is scarce, but suggest substantial declines in the abundance of both species in most assessed areas. The impacting factors behind these patterns vary between species and areas, but include climate, habitat exploitation, fishing, and species-interactions in the coastal food web. Measures to restore and support coastal predatory fish communities should follow an ecosystem-based approach to management and include efforts to regulate fisheries sectors in combination with habitat protection and restoration. Full article

The meagre (Argyrosomus regius), a farmed fish in Mediterranean countries, seasonally migrates from offshore areas to estuaries for reproduction. During the first two years of life, the meagre evidences a certain grade of euryhalinity by staying in brackish waters close to the shore. The aim of the present study was to establish if fingerling growth in brackish water is improved compared to seawater, where current culture procedures are conducted. Three-month-old fingerlings were maintained for 45 days under two different salinity regimens (12 and 39 ppt). Several growth parameters as well as osmoregulatory and metabolic variables were assessed. Specific growth rate and hepatosomatic index values revealed that fingerlings performed better in brackish waters (12 ppt) compared to 39 ppt. This study contributes to optimizing meagre rearing conditions, thereby supporting the role of A. regius in aquaculture diversification. Full article

The determination of exogenous enzyme contributions in live food is important in larval feeding. This study investigated the potential inhibitory effects and contributions of live foods used from 3 to 32 days after hatching (DAH) on protease activities of meagre (Argyrosomus regius) larvae (ML), using in vitro techniques. Enriched rotifer (R), Artemia nauplii (A0), and Artemia metanauplii (A1) were tested. The highest values of protease activities of ML were determined to occur at 7 DAH for the years 2013 and 2014. The lowest values were observed at 15 DAH in 2013 and at 20 DAH in 2014. Protease activities of R, A0, and A1 were 21.76 ± 0.31, 36.00 ± 1.48–29.33 ± 0.93, and 416.44 ± 19.7–403.53 ± 11.85 U/mg protein, respectively (p < 0.05). The highest inhibitions of live foods were observed at 7 DAH. This situation was related to the inadequacy of protease contributions of live feeds, despite the highest protease value of larvae at 7 DAH (p < 0.05). The positive contributions of A1 live food on the protease activities of ML were significant (p < 0.05). The inhibitory effects and positive contributions of live foods on the survival and growth rates of ML should be taken into account for future studies considering the larvae of ML and other marine fish. Full article

Ortho-phosphate inside recirculation aquaculture systems is limited as a consequence of precipitation and regular water exchange rates. To improve plant growth in coupled aquaponics, phosphate fertilizer addition to hydroponics can increase PO₄³⁻-P concentrations inside the process water. We investigated the effects of four PO₄³⁻-P concentrations (<10 (P0), 40, 80, 120 mg L⁻¹) in rearing water on growth performance, feed efficiency, and welfare traits of juvenile African catfish (Clarias gariepinus Burchell, 1822). By trend, optimum specific growth rate of 2.66% d⁻¹ and feed conversion ratio of 0.71 were observed at 40 and 80 mg L⁻¹ PO₄³⁻-P. Higher PO₄³⁻-P significantly affected skin coloration, swimming activity and external injuries, with the palest and inactive fish combined with most external injuries in the P120 group. Mineral and protein contents in the fish remained unaffected, while fat content inside the fillets enriched with increasing PO₄³⁻-P. Inorganic P in blood plasma increased significantly, while phosphate concentrations inside the fillet remained unchanged. We suggest that PO₄³⁻-P concentrations of 40 to 80 mg L⁻¹ do not reduce the performance of African catfish aquaculture, while increased values of 120 mg L⁻¹ affect fish welfare. This allows limited addition of PO₄³⁻-P fertilizer in coupled aquaponics with African catfish to support plant growth. Full article

The skin, gills, and gut are the most extensively studied mucosal organs in fish. These mucosal structures provide the intimate interface between the internal and external milieus and serve as the indispensable first line of defense. They have highly diverse physiological functions. Their role in defense can be highlighted in three shared similarities: their microanatomical structures that serve as the physical barrier and hold the immune cells and the effector molecules; the mucus layer, also a physical barrier, contains an array of potent bioactive molecules; and the resident microbiota. Mucosal surfaces are responsive and plastic to the different changes in the aquatic environment. The direct interaction of the mucosa with the environment offers some important information on both the physiological status of the host and the conditions of the aquatic environment. Increasing attention has been directed to these features in the last year, particularly on how to improve the overall health of the fish through manipulation of mucosal functions and on how the changes in the mucosa, in response to varying environmental factors, can be harnessed to improve husbandry. In this short review, we highlight the current knowledge on how mucosal surfaces respond to various environmental factors relevant to aquaculture and how they may be exploited in fostering sustainable fish farming practices, especially in controlled aquaculture environments. Full article

Nucleobase-Ascorbate Transporter (NAT) family includes ascorbic acid, nucleobases, and uric acid transporters: With broad evolutionary distribution. In vertebrates, four members have been previously recognized, the ascorbate transporters Slc23a1 and Slc3a2, the nucleobase transporter Slc23a4 and an orphan transporter Slc23a3. Using phylogenetic and synteny analysis, we identify a fifth member of the vertebrate slc23 complement (slc23a5), present in neopterygians (gars and teleosts) and amphibians, and clarify the evolutionary relationships between the novel gene and known slc23 genes. Further comparative analysis puts forward uric acid as the preferred substrate for Slc23a5. Gene expression quantification, using available transcriptomic data, suggests kidney and testis as major expression sites in Xenopus tropicalis (western clawed frog) and Danio rerio (zebrafish). Additional expression in brain was detected in D. rerio, while in the Neoteleostei Oryzias latipes (medaka) slc23a5 expression is restricted to the brain. The biological relevance of the retention of an extra transporter in fish and amphibians is discussed. Full article