Fishes, Volume 5, Issue 1 (March 2020) – 10 articles

Changes in different immune activities in the skin mucus of gilthead seabream (Sparus aurata L.) and European sea bass (Dicentrarchus labrax L.) specimens exposed to a constant light–dark photoperiod (12 h L:12 h D) were studied. Samples were collected at 08:00 (light on), 14:00, 20:00 (light off), 02:00, and again at 08:00 to determine immunoglobulin M (IgM) levels, several enzymes related to the immune system, and bactericidal activity. IgM levels were higher during the day in seabream and reached a minimum value at 20:00, but it was hardly affected in sea bass. No significant variations were recorded in the levels of protease and antiprotease. Peroxidase reached its maximum level in seabream at 02:00, the same time that it reached its minimum level in sea bass. Lysozyme showed little variation in seabream, but it was significantly lower at 14:00 than during the rest of the cycle in sea bass. Finally, different interspecific variations on bactericidal activity against Vibrio harveyi were recorded. The findings demonstrate that the immune parameters present in skin mucus of these important fish species are affected by the light–dark cycle and that there are substantial interspecies differences. Full article

Sturgeon raw eggs, caviar and meat obtained from different species reared in an Italian production plant were evaluated for their chemical composition, in order to improve their appreciation on the market and to detect any eventual distinctness related to the species. Mainly, fatty acid (FA) profile of eggs and caviar, determined by Gas-Chromatography coupled to Flame Ionization Detection, showed variability in the interspecific comparison, highlighted by chemometric methods (Linear Discriminant Analysis). Generally, all samples showed a prevalence of unsaturated fatty acids with respect to saturated ones, reaching a content of polyunsaturated fatty acids (PUFA) between the 40% and the 50% of total FA. A remarkable presence of n3 series PUFA was detected in all samples and a selective deposition of many FA into eggs’ cellular membranes, yolk lipid and body fat reserves, imputable to the different biological role of single FA during sturgeon reproduction, was evidenced. Chemical composition of sturgeon flesh samples evidenced a high-protein and medium-fat content, characterized by a FA profile of high nutritional value. Moreover, color parameters (redness, yellowness, brightness, Chroma) were measured on sturgeon fillets, showing many species-specific characteristics of sturgeon meat. Full article

Length–weight relationships (LWRs), condition factors, and their variation over time were analyzed for four exotic freshwater fish (bleak, common carp, pikeperch, and roach) in the Estany d’Ivars i Vila-sana shallow lake in Catalonia, Northern Spain. Fish samples were collected twice a year (early summer and autumn), between 2008 and 2016, by using between three and five multi-mesh nylon gillnets. This study provides novel information about four common exotic fishes outside of their natural range and within the context of a restored shallow lake, where the ichthyologic community is evolving in concordance with the ecosystem conditions and the fish community dynamics. Full article

The caudal fin of teleost fish has become an excellent system for investigating the mechanisms of epimorphic regeneration. Upon amputation of the caudal fin, a mass of undifferentiated cells, called blastema, proliferate beneath the wound-epidermis and differentiate into various cell types to faithfully restore the missing fin structures. Here we describe a protocol that can be used to isolate and culture blastema cells from zebrafish. Primary cultures were initiated from 36 h post-amputation (hpa) blastema and optimal cell growth was achieved using L-15 medium supplemented with 5% fetal bovine serum in plates either coated with fibronectin or uncoated. After seeding, zebrafish blastema cells formed a uniform culture and exhibited polygonal shapes with prominent nucleus, while various cell types were also observed after few days in culture indicating cell differentiation. Upon treatment with all-trans retinoic acid, zebrafish blastema cells differentiated into neuron-like and oligodendritic-like cells. Immunocytochemistry data also revealed the presence of mesenchymal and neuronal cells. The availability of blastema cell cultures could contribute to a better understanding of epimorphic regeneration by providing a mean to investigate the mechanisms underlying blastema cell differentiation. Furthermore, this protocol is simple, rapid, and cost-efficient, and can be virtually applied to the development of any fish blastema cell culture. Full article

Callinectes sapidus is native to the Atlantic coasts of the Americas. In the Mediterranean, it appeared around 1949 and though that it is established in East Mediterranean waters, relevant studies are limited. The aim of the present study is to report quantitative and qualitative data on the blue crab’s biology and ecology in its non-native range, that are indispensable for management purposes. Papapouli Lagoon is in Thermaikos Gulf and is ecologically impacted by the blue crabs. Fyke nets with a 20 mm mesh opening were soaked for 12 to 14 h during each survey. Abiotic environmental parameters were obtained. The length–weight relationships were expressed by the equation W = aL^b. The species’ ecological preferences at Papapouli Lagoon were assessed with PERMANOVA analysis, using the abiotic parameters as factors. Student’s t-tests were used to assess the differences between sexes. The sex ratio of the blue crab’s population was assessed by a Chi-square (χ²) analysis. The sex ratio was found to be 1.28:1, in favour of males. The most dominant group size of male blue crabs was the 61–70 mm of CL and 130–139 mm of CW. Also, the dominant size group of female blue crabs was 60–69 mm of CL and 120–129 mm CW. The maximum abundance of blue crabs was recorded at a salinity range from 24‰ to 25‰ and the water temperature range was from 26 to 28 °C. Full article

Carcinus maenas (the “shore crab” or “European green crab”) is a very proficient invader (considered to be one of the world’s 100 worst invaders by the IUCN) due to its phenotypic plasticity, wide temperature and salinity tolerance, and an extensive omnivorous diet. Native to Atlantic Europe, it has established two well-studied nonindigenous populations in the northwestern Atlantic and northeastern Pacific and less-studied populations in Australia, Argentina and South Africa. Green crabs are eurythermal and euryhaline as adults, but they are limited to temperate coastlines due to more restrictive temperature requirements for breeding and larval development. They cannot tolerate wave-swept open shores so are found in wave-protected sheltered bays, estuaries and harbors. Carcinus maenas has been the subject of numerous papers, with over 1000 published in the past decade. This review provides an up-to-date account of the current published information on the life history and population dynamics of this very important species, including genetic differentiation, habitat preferences, physical parameter tolerances, reproduction and larval development, sizes of crabs, densities of populations, sex ratios, ecosystem dynamics and ecological impacts in the various established global populations of green crabs. Full article

Invasive species are recognized as a major cause of biodiversity decline. Legal regulations relating to the prevention, control, or eradication of invasive species should always be up-to-date, as the failure to recognize the problem, lack of adequate scientific information, or long legal intervals required to prepare the legislation may result in irreversible, possibly catastrophic, outcomes. This implies constant monitoring of the species distribution and levels of establishment, as well as detailed knowledge about its biology to predict dissemination and viability under changing environmental conditions. Pre-screening kits for potential invasive species are valuable tools for policy makers, as they provide information about if and how management measures should be taken. The Freshwater Fish Invasiveness Scoring Kit (FISK) and the Aquatic Species Invasiveness Screening Kit (AS-ISK) have been suggested as reliable tools to assess the potential risk of a species becoming invasive. The present study highlights the spread of the non-native chameleon cichlid Australoheros facetus in several streams of the major river drainages in southern Portugal and compares the fish assemblages and ecological indices in two selected sites in the Vascão and Odelouca rivers. We reviewed the current knowledge on the distribution, physiology, and behavior of A. facetus, and applied the toolkits FISK v2 and AS-ISK to this species to evaluate whether the species should be classified as invasive in Portugal. Field data show high abundance of the species in most streams and dominance in specific hotspots. The scores reached by the kits (FISK v2: 23; AS-ISK: 37) places A. facetus as a species with high potential of invasiveness and support the recent inclusion of this species in the invasive species list in Portugal (Decree-Law 92/2019), but, most of all, highlights the importance of frequent updates in both the field monitoring and the legal regulation and watch lists of invasive organisms. Full article

The lymphocystis disease (LCD) is a viral infection with a high economic impact in gilthead sea bream aquaculture. In this study, genetic estimates associated with lymphocystis disease virus (LCDV) disease susceptibility and growth were determined in sea bream juveniles. Two fish batches (named batch 1 and batch 2) were built from mass spawning and reared under industrial conditions until disease outbreak. At the moment of the sampling (n = 500 specimens for each batch), all animals had the typical LCDV lesions in the skin. For phenotyping, animals were weighted and photographed for image analysis (surface covered and lesion intensity). LCDV DNA copies were quantified in the liver by qPCR. Batch 1 had a higher surface covered and lesion intensity than batch 2, and the body caudal region was the lowest affected region in both batches. The average LCDV DNA copies in liver were higher in the batch 1 than batch 2, and they were positively correlated with severity index (SI) categories (r² = 0.90–0.94). The total number of families evaluated were 150 and 128 for batch 1 and batch 2, respectively, with a high bias in offspring contribution by family and broodstock. Heritabilities for weight and length were 0.18 and 0.14 in batch 1 and 0.06 and 0.05 in batch 2, respectively. Heritability for the number of viral DNA copies was low (<0.08) in both batches. Heritabilities for SI in binary scale were 0.32/0.33 and 0.21/0.24 (underlying liability/Bayesian approach) for batch 1 and batch 2, respectively. Genetic correlations were very high and positive when growth traits (weight and length) or disease traits (LCDV DNA copies and SI) were compared. In contrast, the genetic correlations between growth and disease traits were moderate–high and positive in the batch 1 but negative in batch 2. These results indicate the genetic selection for LCDV susceptibility and growth is feasible in sea bream juveniles, although estimates are highly dependent on the age. The information provided is relevant to designing selective breeding programs in sea bream. Full article

The vulnerability of early fish stages represents a critical bottleneck for fish recruitment; therefore, it is essential to understand how climate change affects their physiology for more sustainable management of fisheries. Here, we investigated the effects of warming (OW; +4 °C) and acidification (OA; ΔpH = 0.5) on the heart and oxygen consumption rates, metabolic enzymatic machinery—namely citrate synthase (CS), lactate dehydrogenase (LDH), and ß-hydroxyacyl CoA dehydrogenase (HOAD), of seabream (Sparus aurata) larvae (fifteen days after hatch). Oxygen consumption and heart rates showed a significant increase with rising temperature, but decreased with pCO₂. Results revealed a significant increase of LDH activity with OW and a significant decrease of the aerobic potential (CS and HOAD activity) of larvae with OA. In contrast, under OA, the activity levels of the enzyme LDH and the LDH:CS ratio indicated an enhancement of anaerobic pathways. Although such a short-term metabolic strategy may eventually sustain the basic costs of maintenance, it might not be adequate under the future chronic ocean conditions. Given that the potential for adaptation to new forthcoming conditions is yet experimentally unaccounted for this species, future research is essential to accurately predict the physiological performance of this commercially important species under future ocean conditions. Full article