Fishes, Volume 3, Issue 1 (March 2018) – 17 articles

For many species, the Mediterranean region harbors distinct lineages that are of conservation concerns. However, many of these are threatened by habitat degradation and by the introduction of non-native species. Here, we assess the status of the native threespine stickleback (Gasterosteus aculeatus) in the Lake Bracciano region in Italy, where stickleback have been historically present. During a dedicated sampling campaign in summer 2015, surveying the potential habitats that sticklebacks commonly occupy, we could not confirm the presence of this species but found introduced species to be often most abundant. Stickleback are thus likely to either have become extinct over the last decades or be on the verge to extinction in the Lake Bracciano region. Full article

Streptococcus agalactiae and Aeromonas hydrophila have been recognized as the causative agents of mortality in tilapia larvae with single infection and coinfection. The objective of this study was to evaluate the efficacy of maternal transfer and offspring protection from the immunization of monovalent and bivalent vaccines on Nile tilapia (Oreochromis niloticus) broodstock and larval immunization. Four groups of broodstock were intraperitoneally injected with formalin killed whole-cells of S. agalactiae (Sa group), A. hydrophila (Ah group), the bivalent mixed vaccine of them (Biv group), and phosphate-buffered saline as a control (Pbs group). Immunization of the larvae produced from immunized broodstock with a bivalent vaccine (Biv1 group) and Pbs (Pbs1 group) was performed by immersion at 20 days after hatch. Larvae produced from the Pbs group were unvaccinated as the control (Pbs2 group). Changes in the specific antibody and relative percent survival were measured. The Sa and Ah groups that could increase specific antibodies and protection against pathogenic bacteria were challenged with the homologous bacteria. The Biv group stimulated and protected against both S. agalactiae and A. hydrophila. The specific antibody of the Biv1 group was higher than the Pbs1 and Pbs2 groups. The last observation in this study showed that the relative percent survival of the Biv group after challenged S. agalactiae, A. hydrophila, and coinfection were 74.74 ± 3.18%, 73.81 ± 8.58%, and 71.48 ± 5.70%, respectively. The use of bivalent vaccines on the broodstock and larvae may be a strategy to reduce mortality in Nile tilapia larvae caused by single pathogen infection of S. agalactiae and A. hydrophila, or coinfection with both S. agalactiae and A. hydrophila. Full article

Aquatic fern Azolla pinnata comprises significant high food value with a good proportion of protein, vitamins, and minerals. This study was carried out to examine the effect of fresh A. pinnata as a substitution of commercial fish feed (CFF) for Thai silver barb Barbonymus gonionotus. Post fingerlings of B. gonionotus were reared in five treatments, labeled T₁ to T₅, by substituting 0%, 25%, 50%, 75%, and 100% protein of CFF with A. pinnata protein (dry matter basis) respectively for 56 days. The specific growth rate, net production rate, protein efficiency ratio, proximate composition, and overall conditions of fish were not significantly varied between the fish reared completely with CFF and 25% substitution with A. pinnata. However, a significantly higher profit rate (431.49 USD ha⁻¹ 56 day⁻¹) was calculated for fish reared in T₂ than other treatments. In contrast, there was a significant reduction of growth and other parameters of the fish that were observed in the case where more than 25% CFF was substituted with A. pinnata. The poorest performance was observed in fish fed completely with A. pinnata, at T₅. Based on the results, 25% of CFF of Thai silver barb could be substituted with fresh A. pinnata without significantly lowering their growth and product quality and could contribute significant to a higher profit margin. Full article

The Amazon sailfin catfish Pterygoplichthys pardalis is native to the Amazon River basin. It has since expanded its range to North America, the Caribbean, and more recently to South Asia, as with some of its congeners. Our paper reviews recent data from Bangladesh, clarifies taxonomic identification, and examines the potential effects of P. pardalis and congeneric species on local aquatic ecosystems and elsewhere in South Asia. Range expansions there probably reflect aquarium releases and escapes from aquaculture farms, as exacerbated by dispersal due to storm flooding and in impacted waters like irrigation canals. Given their potential ecosystem-level effects, we also review potential control mechanisms and human use for these invasive loricariids. Full article

Locomotion-based behavioural endpoints have been suggested as suitable sublethal endpoints for human and environmental hazard assessment, as well as for biomonitoring applications. Larval stages of the sand goby (Pomatoschistus minutus) possess a number of attractive qualities for experimental testing that make it a promising species in behavioural ecotoxicology. Here, we present a study aimed at developing a toolkit for using the sand goby as novel species for ecotoxicological studies and using locomotion as an alternative endpoint in toxicity testing. Exposure to three contaminants (copper (Cu), di-butyl phthalate (DBP) and perfluorooctanoic acid (PFOA) was tested in the early life stages of the sand goby and the locomotion patterns of the larvae were quantified using an automatic tracking system. In a photo-motor test, sand goby larvae displayed substantially higher activity in light than in dark cycles. Furthermore, all tested compounds exerted behavioural alterations, such as hypo- and hyperactivity. Our experimental results show that sand goby larvae produce robust and quantifiable locomotive responses, which could be used within an ecotoxicological context for assessing the behavioural toxicity of environmental pollutants, with particular relevance in the Nordic region. This study thus suggests that sand goby larvae have potential as an environmentally relevant species for behavioural ecotoxicology, and as such offer an alternative to standard model species. Full article

This study aimed to evaluate the in vitro activity of Zanthoxylum rhoifolium bark (Zr-b) extracts against pathogenic aquatic oomycete/fungal isolates that cause different diseases in native European crayfish resulting in an elevated mortality rate and severe economic repercussions. n-hexane, chloroform, chloroform–methanol (9:1) and methanol extracts of Zr-b were used to evaluate the antifungal activity against the strain UEF88662 of Aphanomyces astaci (oomycete) and the strain SMM2 of Fusarium avenaceum (fungus). The anti-oomycete and antifungal activity was quantitatively evaluated by growth, survival and sporulation microbiological assays. The extracts tested demonstrated a dose-dependent inhibitory effect on oomycete and fungal growth and survival, as well as on the production of oomycete and fungal spores. This work presents alternatives for the treatment and prevention of the spreading of Aphanomyces astaci and Fusarium avenaceum, the etiological agents of the diseases crayfish plague and brown spot disease, respectively. The antifungal properties of Zanthoxylum rhoifolium bark extracts warrant further research on their use in the prevention and treatment of both oomycete and fungal diseases. The antifungal properties of Zanthoxylum rhoifolium bark extracts, shown in vitro, indicate the possibility of their use in new therapeutic and prophylactic strategies, providing perspectives for the design of in vivo studies. Full article

Blooms of the planktonic alga Prymnesium parvum pose a global threat, causing fish kills worldwide. Early studies on the exposure of fish to P. parvum indicate that toxic effects are related to gill damage. The more strictly defined concept of adverse outcome pathways has been suggested as a replacement for the mode of action in toxicology studies. In this study, rainbow trout (Onchorhyncus mykiss) were exposed to P. parvum. During exposure, oxygen consumption was determined by respirometry, and ventilation and coughing rate were determined via video surveillance. Per breath oxygen consumption was calculated to assess the ventilation effort to obtain a unit of oxygen. A second experiment monitored fish behavior to assess recovery. The results indicated that oxygen consumption initially increased, but on average fell below the standard oxygen consumption at 70% relative exposure. Being a function of ventilation frequency and oxygen consumption, the per breath oxygen consumption decreased throughout exposure. Behavioral results determined that short-term P. parvum exposure subsequently caused the exposed fish to seek flow refuge immediately and to a greater extent than unexposed fish. The adverse outcome pathway of P. parvum on rainbow trout is that P. parvum acts as a gill irritant resulting in non-recoverable respiratory failure. Full article

The effects of a peracetic acid-based disinfectant product (Aquastart^®) were assessed on some hematological parameters, histological aspects and skin bacterial load of rainbow trout, likewise bacterial load of the rearing tank water. A total of 180 healthy rainbow trout weighing 124.65 ± 10 g were divided into two groups, each in three replicates in flow-through tanks. First group was exposed to Aquastart at 8.9 ppm for 30 min and second group was considered as the control. The fish were then reared for 60 days prior to sampling for hematological and histological studies. The lowest bacterial load level in both water columns and trout skin were observed in the treated trout (p < 0.05). Meanwhile, no significant impact on growth performance was recorded between treated and control fish. The immunocompetent cells population size in control fish were significantly lower than treated fish (p < 0.05). Histologically, no evidence of abnormality was seen in the gills, kidney, and liver tissues of treated fish. These results showed that application of Aquastart at 8.9 ppm is safe for use in flow-through tanks farming rainbow trout. Full article

Understanding the protective role of fish skin is critical to improving the development of aquaculture, since skin is the main surface that separates the animal from its always hazardous environment. Many techniques have been used for its study, but certain structural characteristics of fish skin still remain not clearly understood. That is the case with scales, which have always been attributed a mere protective role, but which are proving to have more functions than it was traditionally thought. To acquire a deeper knowledge, scales from six different regions of gilthead seabream (Sparus aurata L.) were studied and measured by image analysis. Results prove that scales from the base of the dorsal fin are larger than those in other parts of the fish body while scales from the peduncle are the smallest of the skin. Furthermore, a technique relatively new in this field, known as atomic force microscopy (AFM), was used to obtain representations of the ultrastructure of the scales and measure certain features such as the circuli and the lines in the basal layer. The data obtained allowed us to compare the height of circuli among the different scales, showing that they were higher in scales from the dorsum and the operculum. The present results introduce a nanostructural model of the scales of gilthead seabream that might serve as a useful guideline for future studies. Full article

This study describes de novo transcriptome sequencing and annotation analyses for the head kidney of the sub-Antarctic notothenioid fish Eleginops maclovinus, a sister group of the Antarctic notothenioid fish clade. Moreover, E. maclovinus is one of the most eurythermal and euryhaline representatives of the Notothenioidei suborder. RNA-seq data were generated by the 454 GS Junior system, resulting in 11,207 contigs that were then assembled by the Genomic Workbench CLC software. The transcriptome was annotated by BLASTing each sequence against the universal, non-redundant NCBI database (National Center for Biotechnology Information) using the AUSTRAL-omics computer cluster. A significant number of transcripts related to innate and adaptive immunity were found in the sequences, which could be used as references in future immunological studies in E. maclovinus. Full article

Stress is one of the main problems of farmed fish, where it has been seen to result in a variety of disorders and negative effects. It is considered very important to minimize such effects and one option is the use of dietary additives. In the present experiment, meagre (Argyrosomus regius) specimens were fed three different diets: a control diet consisting of a commercial feed, a tryptophan-supplemented diet and an aspartate-supplemented diet. For each diet, fish were divided into three subgroups: non-stressed (resting), exposed to crowding or air-exposed. Just before the stress, and one and six hours post-stress, serum samples were taken to study several immune parameters (protease, antiprotease, peroxidase and lysozyme) and the bactericidal activity against three fish-pathogenic bacteria (Vibrio angillarum, V. harveyi and Photobacterium damselae subsp. piscicida). The results demonstrated that feeding the animals with the supplemented diets modulates the seric immune parameters, particularly when animals were stressed by air exposure. Full article

Neogobius melanostomus, the round goby, was recorded by underwater video feeding on crushed dreissenid mussels at a depth of 12 m in Georgian Bay of Lake Huron, a Laurentian Great Lake. In the video, gobies used rotational or twist feeding to tear away particles from crushed mussels. At least 43 examples of this feeding maneuver occur in the video. Up to 120 gobies m⁻² were visible at a time in the video. Mean standard length of gobies appearing in the video was 37 mm. Mean standard length of fish exhibiting twist feeding was larger, 48 mm. Mean size of intact mussels in visible clusters was about 10 × 20 mm, a size which exceeds the gape width of the largest gobies observed in the video. Neogobius melanostomus is known to use twisting to wrest small attached mussels from the substrates which can be crushed by their pharyngeal teeth. I surmise that the behavior observed in the video is an opportunistic manifestation of this inherent behavioral adaptation to overcome gap limitation and exploit a temporary windfall of food. Full article

Aquaculture feed manufacturers and producers increasingly recognize the importance of mycotoxins, which contaminate plant-based meals used in compound aquafeeds, and their potential to negatively impact production. Though data on the worldwide occurrence of legislated mycotoxins e.g., trichothecenes and zearalenone (ZEN) are well documented, relatively little information is available regarding other mycotoxins also produced by Fusarium, notably moniliformin (MON). Given that MON is known to affect the survival, growth, skeletal formation and bone mineralization in terrestrial species, its widespread occurrence on maize and maize by-products typically used in aquaculture makes it relevant to study these parameters in teleost fish. In the present work we have tested the effect of MON exposure on survival, bone development and mineralization using zebrafish (Danio rerio) as a model species and fish derived osteo-chondroprogenitor cell line for in vitro studies. Moniliformin exposure did not decrease bone mineralization in zebrafish larvae or extracellular matrix mineralization in the mineralogenic cell line VSa13. Here, the minimal in vitro cytotoxicity concentration was found to be 1000 µg L⁻¹ MON. Incidence of deformities was also not altered by MON at the concentration tested (450 µg L⁻¹) although larval growth was affected, as shown by a decrease in the standard length of exposed specimens at 20 days post fertilization. Survival decreased significantly in larvae exposed to MON concentrations higher than 900 μg L⁻¹. Influence of MON on survival and growth might be relevant for aquaculture industry. As MON is a water-soluble mycotoxin, its leaching from feed is highly probable, so MON assimilation into the surrounding aqueous environment should also be considered. Tested levels in fish larvae are within the reported occurrence levels of MON in commercial feed and plant meals. Full article

Muxama is a traditional highly-valued food product prepared from dry-cured tuna loins in southern Portugal and Spain. The production procedure has seen little change over the last centuries. The muxama’s stability is due to reduced water activity. In addition, the drying method has secondary effects on characteristics of flavor, color, and the nutritional value of the product. Our objectives were to describe the dynamics of important physicochemical parameters such as moisture content, water activity (a_W), NaCl concentration (as water–phase salt, Z^NaCl), pH and color, during the salting and drying stages of muxama production, and to test the effect(s) of changes in the traditional processing conditions followed in southern Portugal, aiming at optimizing the production procedure. The lowest values of moisture and a_W and highest Z^NaCl obtained after drying tuna loins for seven days at 20 °C exceeded the values reported for commercial products and have impact on the appearance (color) of the product. Therefore, drying tuna loins at lower temperatures (ca. 14 °C) is probably more appropriate. The results obtained in this study could be used in the design of future experiments at other conditions and to assess other quality parameters, e.g., total volatile base nitrogen (TVB-N), thiobarbituric acid reactive substances (TBA-RS), microorganism abundance and sensory attributes, and subsequent validation trials. Full article

The harvesting of bait through digging in coastal mudflats is practiced for recreational and commercial purposes in European coastal systems including the Ria de Aveiro coastal lagoon on the northwest Atlantic coast of Portugal. The scale of harvesting in the Ria de Aveiro has recently increased due to the current economic climate in Portugal, with targeting of the polychaete, Diopatra neapolitana species or “casulo” as it is widely known in the Aveiro region. The national authorities have attempted to control casulo digging by issuing a regulation (Ordinance) in 2014 on the maximum daily catch limit to be caught by each individual. The daily catch limit is intended to represent the Maximum Sustainable Yield (MSY) for casulo beyond which overfishing will occur. The monitoring of the regulatory measures is expected to be conducted through on-site inspections in the digging areas. However, weak law enforcement was noticed, while there is also controversy over the daily catch limit (quota) stipulated by the Ordinance. To this end, the current study attempted to assess digging activities through remote monitoring and random inspections for a better policy enforcement of the national regulation. In addition, different harvesting scenarios were employed through a simplified bioeconomic model to attribute the current and future harvesting trends of bait digging in Aveiro coastal lagoon. The study findings indicate that remote monitoring coupled with some onsite interviews could be a more effective approach for the implementation of the current bait digging policy. Further, the results point to a distinctive discrepancy between the daily catch amount (MSY) introduced by the national legislation and the study findings which should be further scrutinized. The diggers seem to have reached the sustainable harvest identified by the present research. The current economic hardship in Portugal and the low profitability in similar employment sectors will possibly attract more diggers and increase harvesting in the near future. An increased harvest would likely trigger overfishing of D. neapolitana with unknown consequences for the population of the species as well as the aquatic ecosystem. The socio-economic and environmental effects are yet to be further clarified with more detailed data and advanced modeling techniques to ensure the sustainability of the activity. Full article

Replacement of fishmeal with plant ingredients will introduce not only plant oil and protein but also phytosterol to the fish diet. Mammals strictly restrict the uptake of phytosterol at intestinal epithelial cells by regulating the gene expressions of sterol uptake and excretion proteins; however, phytosterol is found in the fish muscle and other organs. In order to assess the ability of phytosterol uptake by the intestinal epithelial cells of fish, no-sterol diet, cholesterol-, and β-sitosterol-containing diet was separately administered to zebrafish, and the relative mRNA expressions related to sterol uptake and excretion were evaluated. Gene expression of Niemann-Pick C1-like protein 1 in the sitosterol-fed group was significantly higher than that of the cholesterol-fed group (p < 0.05). The expression of apolipoprotein A-I gene was also higher in the sitosterol-fed group than that in the no-sterol and cholesterol-fed groups. The expressions of ATP-binding cassette, sub-family G, member 5 and 8, were significantly higher in the sitosterol-fed group, compared to the no-sterol group. Regarding the gene expression of ATP-binding cassette sub-family A, member 1, the sitosterol-fed group showed higher expression level compared to the other groups (p < 0.01). These results suggest that fish should be tolerant to phytosterols in contrast to mammals. Full article