Rapid blood acid-base regulation by European sea bass (Dicentrarchus labrax) in response to sudden exposure to high environmental CO2

Fish in coastal ecosystems can be exposed to acute variations in CO2 of between 0.2-1 kPa CO2 (2,000 - 10,000 µatm). Coping with this environmental challenge will depend on the ability to rapidly compensate the internal acid-base disturbance caused by sudden exposure to high environmental CO2 (blood and tissue acidosis); however, studies about the speed of acid-base regulatory responses in marine fish are scarce. We observed that upon sudden exposure to ∼1 kPa CO2, European sea bass (Dicentrarchus labrax) completely regulate erythrocyte intracellular pH within ∼40 minutes, thus restoring haemoglobin-O2 affinity to pre-exposure levels. Moreover, blood pH returned to normal levels within ∼2 hours, which is one of the fastest acid-base recoveries documented in any fish. This was achieved via a large upregulation of net acid excretion and accumulation of HCO3− in blood, which increased from ∼4 to ∼22 mM. While the abundance and intracellular localisation of gill Na+/K+-ATPase (NKA) and Na+/H+ exchanger 3 (NHE3) remained unchanged, the apical surface area of acid-excreting gill ionocytes doubled. This constitutes a novel mechanism for rapidly increasing acid excretion during sudden blood acidosis. Rapid acid-base regulation was completely prevented when the same high CO2 exposure occurred in seawater with experimentally reduced HCO3− and pH, likely because reduced environmental pH inhibited gill H+ excretion via NHE3. The rapid and robust acid-base regulatory responses identified will enable European sea bass to maintain physiological performance during large and sudden CO2 fluctuations that naturally occur in coastal environments.

Sinop İli Su Ürünleri Üretiminin Mevcut Durumu ve Türkiye Su Ürünleri Üretimindeki Yeri

In the present study, the production amount in the last five years (2015-2019) of Sinop province, which is located in the Black Sea Region and a significant part of fisheries production is carried out, was evaluated. For this purpose; Sinop Provincial Directorate of Agriculture and Forestry and TUIK (Turkish Statistical Institute) data were used. There are 2.326 commercial fishermen and 444 fishing boats in Sinop province. In the sea area of Sinop, 5 enterprises still produce culture fish in cages. The 2 potential marine culture areas identified in Sinop have an annual production capacity of 32.430 tons (31 enterprises). In addition, 5 bivalves (4.940 tons/year) and 1.000.000 number/year capacity juvenile fish production facilities are at the project stage. The total fisheries production of Sinop Province in 2019 was 34.620,9 tons, and 1.505 tons were obtained from aquaculture. In addition to these, 3.924 tons of fish processing facilities per year, and 35 tons of fish meal and oil processing facilities per year are operated. 66% of sea fish caught in Sinop are anchovy (Engraulis encrasicolus ponticus), 16% sprat (Sprattus sprattus phalericus), 13% horse mackerel (Trachurus trachurus), 3% bluefish (Pomatomus saltatrix) and 2% consists of other species. The most preferred marine fish by the consumers are anchovy (Engraulis encrasicolus ponticus), horse mackerel (Trachurus trachurus), whiting (Merlangus merlangus), red mullet (Mullus barbatus), bluefish (Pomatomus saltatrix), turbot (Psetta maxima) and bonito (Sarda sarda) and sea bream (Sparus aurata), sea bass (Dicentrarchus labrax) and rainbow trout (Oncorhyncus mykiss) are the culture fish species offered for sale throughout the year.

Recovery of Haemal Lordosis in European Seabass Dicentrarchus labrax (Linnaeus 1758)

Lordosis of the haemal part of the vertebral column is a frequent abnormality in reared fish. Haemal lordosis develops during the late larval and early juvenile life stages of fish, mainly due to the high swimming activity of the fish in the rearing tanks. In the present study, we have examined whether haemal lordosis recovers during the growth of European seabass. Furthermore, we aimed to develop simple morphometric indices (PrAn1 and PrAn2) that might link the severity of lordosis at the juvenile stage with fish morphological quality at harvesting. At 111 days post-hatching (dph, 53 ± 4 mm standard length, SL), 600 seabass juveniles with lordotic (L, 200 fish) or normal (N, 400 fish) external morphology were selected and introduced in a common tank. At 150 dph (75 ± 7 mm SL), 350 fish were randomly selected, pit-tagged and transferred to a sea cage for on-growing up to 502 dph (234 ± 16 mm SL). The morphological examination of the fish at 150 and 502 dph revealed that 60% (46 out of 77) of L juveniles turned into normal phenotype by the end of on-growing period. Interestingly, 56% of the fish with recovered external morphology (N-Rec) presented either a completely normal vertebral column (31%) or minor abnormalities of individual vertebrae (25%). Following the results of geometric morphometric analysis, the differences in the body shape between N-Rec and N fish were not statistically significant (p > 0.05, canonical variate analysis). The examined morphometric indices were effective in discriminating the normal fish from 58% (PrAn1) to 65% (PrAn2) of lordotic juveniles. Results are discussed with respect to the mechanism of lordosis recovery, and spotlights on their application for quality control and cull out of the abnormal fish in commercial hatcheries.

THE FIRST OUTBREAK OF VIRAL ENCEPHALOPATHY AND RETINOPATHY IN FARMED SEA BASS (Dicentrarchus labrax) IN SLOVENIA

Viral encephalopathy and retinopathy (VER) is considered a serious disease of several marine fish species, caused by RNA virus belonging to the family Nodaviridae, genus Betanodavirus. The disease is spread almost worldwide and causes significant losses among diseased fish. It is characterised by vacuolation of the central nervous system and the retina. In July 2018, behavioural abnormalities i.e. altered swimming, swirling and vertical floating as well as lethargy and anorexia were observed in farmed sea bass (Dicentrarchus labrax) in the Gulf of Piran (Slovenia), associated with significant mortality. The disease initially occurred in juvenile sea bass, but later market-sized fish also became affected. Diseased fish displayed ocular opacity and multifocal skin ulceration on the head. Emaciation in some fish was also evident. Histopathology revealed characteristic vacuolation in the brain and retina. Performing a RT-PCR and RT-qPCR techniques, we have identified and confirmed the presence of betanodavirus nucleic acid in ocular and brain tissues. In addition, concentrations of the causative agent of VER in spleen and kidney did result in significantly higher viral yield than expected. Phylogenetic analysis showed that Slovenian isolate belongs to RGNNV species of betanodaviruses. Based on the clinical signs, gross and typical microscopic lesions and results of molecular analyses, we can conclude that farmed sea bass from the Gulf of Piran were affected with VER. To the best of our knowledge, this is the first report of VER in Slovenia.Key words: viral encephalopathy and retinopathy; betanodavirus; sea bass; histopathology; RT-qPCR PRVI IZBRUH VIRUSNE ENCEFALOPATIJE IN RETINOPATIJE PRI GOJENIH BRANCINIH (Dicentrarchus labrax) V SLOVENIJI Izvleček: Virusna encefalopatija in retinopatija (VER) je nevarna bolezen številnih vrst morskih rib, ki jo povzroča nevrotropni RNA virus iz družine Nodaviridae, rod Betanodavirus. Bolezen je razširjena skoraj po vsem svetu in povzroča visok pogin okuženih rib. Zanjo so značilne vakuole v centralnem živčnem sistemu in retini. Konec julija 2018 so v ribogojnici v Piranskem zalivu pri brancinih opazili nepravilno plavanje, vrtenje in postavljanje v vertikalno smer ter letargijo in neješčnost, brancini so množično poginjali. Bolezen se je najprej pojavila pri mladicah, nato tudi pri konzumnih kategorijah brancinov. Obolele ribe so imele sivo-motna očesna zrkla ter multifokalne kožne razjede na glavi, posamezne so bile shujšane. S histopatološko preiskavo smo ugotovili značilne vakuole v možganih in retini. Z molekularnima metodama RT-PCR in RT-qPCR smo potrdili prisotnost nukleinske kisline betanodavirusa v očesnem zrklu in možganih. Koncentracije virusa, ki so bile signifikantno višje od pričakovanih, smo ugotovili tudi v vranici in ledvicah. Na podlagi kliničnih znakov, makroskopskih in tipičnih histopatoloških sprememb ter rezultatov molekularnih preiskav lahko zaključimo, da so gojeni brancini v ribogojnici v Piranskem zalivu zboleli za VER. Opisani izbruh je prvi potrjeni primer te bolezni v Sloveniji.Ključne besede: virusna encefalopatija in retinopatija; betanodavirus; brancin; histopatologija; RT-qPCR

Effective and Low-Maintenance IMTA System as Effluent Treatment Unit for Promoting Sustainability in Coastal Aquaculture

Integrated multitrophic aquaculture (IMTA) is a versatile technology emerging as an ecological and sustainable solution for traditional monoculture aquacultures in terms of effluent treatment. Nevertheless, IMTA is still poorly applied in aquaculture industry due to, among other reasons, the lack of effective, low-investment and low-maintenance solutions. In this study, one has developed a practical and low maintenance IMTA-pilot system, settled in a semi-intensive coastal aquaculture. The optimisation and performance of the system was validated using Ulva spp., a macroalgae that naturally grows in the fishponds of the local aquaculture. Several cultivation experiments were performed at lab-scale and in the IMTA-pilot system, in static mode. The specific growth rate (SGR), yield, nutrient removal, N and C enrichment, protein and pigment content were monitored. Ulva spp. successfully thrived in effluent from the fish species sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) production tanks and significantly reduced inorganic nutrient load in the effluent, particularly, NH4+, PO43− and NO3−. The enrichment of nitrogen in Ulva spp.’s tissues indicated nitrogen assimilation by the algae, though, the cultivated Ulva spp. showed lower amounts of protein and pigments in comparison to the wild type. This study indicates that the designed IMTA-pilot system is an efficient solution for fish effluent treatment and Ulva spp., a suitable effluent remediator.

Iodine Content of Wild and Farmed Seafood and Its Estimated Contribution to UK Dietary Iodine Intake

Iodine is an important nutrient for human health and development, with seafood widely acknowledged as a rich source. Demand from the increasing global population has resulted in the availability of a wider range of wild and farmed seafood. Increased aquaculture production, however, has resulted in changes to feed ingredients that affect the nutritional quality of the final product. The present study assessed the iodine contents of wild and farmed seafood available to UK consumers and evaluated its contribution to current dietary iodine intake. Ninety-five seafood types, encompassing marine and freshwater fish and shellfish, of wild and farmed origins, were purchased from UK retailers and analysed. Iodine contents ranged from 427.4 ± 316.1 to 3.0 ± 1.6 µg·100 g−1 flesh wet weight (mean ± SD) in haddock (Melanogrammus aeglefinus) and common carp (Cyprinus carpio), respectively, being in the order shellfish > marine fish > freshwater fish, with crustaceans, whitefish (Gadiformes) and bivalves contributing the greatest levels. Overall, wild fish tended to exhibit higher iodine concentrations than farmed fish, with the exception of non-fed aquaculture species (bivalves). However, no significant differences were observed between wild and farmed Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and turbot (Psetta maxima). In contrast, farmed European seabass (Dicentrarchus labrax) and seabream (Sparus aurata) presented lower, and Atlantic halibut (Hippoglossus hippoglossus) higher, iodine levels than their wild counterparts, most likely due to the type and inclusion level of feed ingredients used. By following UK dietary guidelines for fish consumption, a portion of the highest oily (Atlantic mackerel, Scomber scombrus) and lean (haddock) fish species would provide two-thirds of the weekly recommended iodine intake (980 µg). In contrast, actual iodine intake from seafood consumption is estimated at only 9.4–18.0% of the UK reference nutrient intake (140 µg·day−1) across different age groups and genders, with females obtaining less than their male equivalents.

Pituitary Hormones mRNA Abundance in the Mediterranean Sea Bass Dicentrarchus labrax: Seasonal Rhythms, Effects of Melatonin and Water Salinity

In fish, most hormonal productions of the pituitary gland display daily and/or seasonal rhythmic patterns under control by upstream regulators, including internal biological clocks. The pineal hormone melatonin, one main output of the clocks, acts at different levels of the neuroendocrine axis. Melatonin rhythmic production is synchronized mainly by photoperiod and temperature. Here we aimed at better understanding the role melatonin plays in regulating the pituitary hormonal productions in a species of scientific and economical interest, the euryhaline European sea bass Dicentrarchus labrax. We investigated the seasonal variations in mRNA abundance of pituitary hormones in two groups of fish raised one in sea water (SW fish), and one in brackish water (BW fish). The mRNA abundance of three melatonin receptors was also studied in the SW fish. Finally, we investigated the in vitro effects of melatonin or analogs on the mRNA abundance of pituitary hormones at two times of the year and after adaptation to different salinities. We found that (1) the reproductive hormones displayed similar mRNA seasonal profiles regardless of the fish origin, while (2) the other hormones exhibited different patterns in the SW vs. the BW fish. (3) The melatonin receptors mRNA abundance displayed seasonal variations in the SW fish. (4) Melatonin affected mRNA abundance of most of the pituitary hormones in vitro; (5) the responses to melatonin depended on its concentration, the month investigated and the salinity at which the fish were previously adapted. Our results suggest that the productions of the pituitary are a response to multiple factors from internal and external origin including melatonin. The variety of the responses described might reflect a high plasticity of the pituitary in a fish that faces multiple external conditions along its life characterized by marked daily and seasonal changes in photoperiod, temperature and salinity.

Tracking and Analysis of the Movement Behavior of European Seabass (Dicentrarchus labrax) in Aquaculture Systems

Monitoring and understanding fish behavior is crucial for achieving precision in everyday husbandry practices (i.e. for optimizing farm performance), and for improving fish welfare in aquaculture. Various intelligent monitoring and control methods, using mathematical models, acoustic methods and computer vision, have been recently developed for this reason. Here, a tracking algorithm based on computer vision that extracts short trajectories of individual European seabass in both recirculating aquaculture systems and sea cages was developed using videos from network cameras. Using this methodology, parameters such as instantaneous normalized speed, travel direction and preference for the tank surface by European seabass could be quantified. When testing the sensitivity of this algorithm for detecting fish swimming variations under different husbandry scenarios, we found that the algorithm could detect variations in all of the abovementioned parameters and could potentially be a useful tool for monitoring the behavioral state of European seabass.