Fishes, Volume 3, Issue 2 (June 2018) – 7 articles

The interaction between the immune and endocrine systems has long been recognized in vertebrates. In fish, it is known that the prevalence and intensity of such infections are higher in males than in females and probably related to sex steroid hormone levels. In addition, the immune response in the fish gonad tissues is specifically regulated to prevent infertility. This condition is used by some pathogens to colonize the fish gonad, evade the systemic immune response, and so spread to the progeny. This review brings up to date our knowledge concerning fish gonad immunity and its regulation, immune-endocrine interactions, and how some pathogens use this tissue to spread to the progeny through vertical transmission. More specifically, we will look at the case of the European sea bass and nodavirus (NNV). Sea bass is a very susceptible fish species to NNV infections, and this virus has been associated to vertical transmission since it is detected in gonad fluids as well as in testicular gametes. In fact, sea bass immunity in the gonad is regulated in a very different way to other target tissues (brain and retina) or immune-relevant tissues (head-kidney or spleen). Full article

The presence of heavy metals in freshwater fish represents a global public health issue. The current study aimed to determine the heavy metal concentration and toxicity in some freshwater fish species collected from the Tigris River in Baghdad. Out of the many fish species in Iraq, the current study selected the Genus Barbus as it represents the most popular fish food in Iraq. The sample included twenty fishes and the selected sample locations covered two industrial areas in Baghdad (one north of Baghdad and one south of Baghdad). The levels of heavy metals were determined by using an atomic absorption spectrophotometer (AAS). The results showed that concentrations of heavy metals in the sampled fishes exceeded the acceptable levels for food sources for human consumption. The results of this study showed high levels of cadmium and chromium levels in the tissues of the selected fish sample. Cd and Cr were among the highest concentrations and both exceeded the World Health Organization and Food and Agriculture Organization of the United Nations acceptable levels for heavy metals in fishes. Full article

Pool barb (Puntius sophore) is an important small indigenous species of Bangladesh, belonging to the family Cyprinidae of the order Cypriniformes. The main objectives of the present study were to identify the breeding season of Pool barb through observation of the gonadosomatic index (GSI), fecundity, oocytes diameter, and gonadal histology of the species. GSI was calculated and fecundity was determined by the gravimetric method. Interestingly, the highest value of GSI was 15.43 ± 2.20 for the month of April at Gazipur while it was 15.60 ± 1.74 in June for Jessore. In Gazipur, the highest fecundity (5053 ± 878.27) was recorded in the month of April and the highest fecundity (5433 ± 968.26) was recorded in the month of June for Jessore. Histology of the ovary of Pool barb shows the presence of early and late perinucleolar stage of oocytes during March indicating immature oocyte. Histological data revealed that the spawning season of Pool barb starts from March to July with a peak during April to May for Gazipur region and May to July for Jessore region. Finally, these results can be concluded that breeding season may vary from region to region due to environmental as well as other factors. Full article

The skin mucus of fish is in permanent contact with the aquatic environment. Data from the analysis of the chemical composition of skin mucus could potentially be used for monitoring the health status of the fish. Knowledge about mucus composition or change in composition over time could also contribute to understanding the aetiology of certain diseases. The objective of the present study was the development of a workflow for non-invasive sampling of skin mucus from farmed salmon (Salmo salar) for the targeted and untargeted detection of small metabolites. Skin mucus was either scraped off, wiped off using medical wipes, or the mucus’ water phase was absorbed using the same type of medical wipes that was used for the wiping method. Following a simple filtration step, the obtained mucus samples were subjected to hydrophilic interaction chromatography coupled to high-resolution mass spectrometry. Post-acquisition processing included the targeted analysis of 86 small metabolites, of which up to 60 were detected in absorbed mucus. Untargeted analysis of the mucus samples from equally treated salmon revealed that the total variation of the metabolome was lowest in absorbed mucus and highest in the scraped mucus. Thus, future studies including small-molecule metabolomics of skin mucus in fish would benefit from a sampling regime employing absorption of the water phase in order to minimize the bias related to the sampling step. Furthermore, the absorption method is also a less invasive approach allowing for repetitive sampling within short time intervals. Full article

The monogenean Gyrodactylus gasterostei and its host, the three-spined stickleback Gasterosteus aculeatus, were employed as a model system to investigate the influence of gyrodactylid maturity on host transfer. Laboratory experiments included the determination of maturity (presence of a male copulatory organ) and reproductive status (presence of a daughter parasite) of the transmitting worms. Parasites with a male copulatory organ were more likely to abandon the host and attempt a host transfer. Additionally, in vivo video observation suggested that detached worms employ water turbulence to assist their effective transfer onto a new host. Full article

During the last few decades the fish community has changed substantially along the Eastern Mediterranean continental shelf, which is a hotspot of invasion by species that had migrated via the Suez Canal. Trawl data from the Israeli coast spanning two periods (1990–1994 and 2008–2011) were compared to identify species with substantial variation in their relative abundance between the two periods. The aim of this study was to examine if certain ecological traits characterize fish species showing an increase or decrease in relative abundance, and if non-indigenous fishes with strongly increasing populations may have caused the decline of native species with similar habitats and diets. We found that the main predictors of population trends were species length, habitat affinity, and maximum depth, with larger and soft bottom species displaying decreasing abundances. Comparing native and non-indigenous fishes with similar habitat and diet, we found a potential for competitive impact of the Indo-Pacific Plotosus lineatus and two Upeneus spp. on the native Mullus species. However, competition with non-indigenous fishes could not generally explain the dramatic decline of many other native species between the two study periods. Alternative causes, such as fishery pressure and increasing water temperature, are discussed. Full article

The worldwide interest in developing the culture of nonconventional fish species determines the need to increase knowledge in different aspects of their basic physiology, as well as in the application of such information into practical protocols to be used in their feeding, reproduction, and general handling [...]
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