Influence of Seaweed Aquaculture on Marine Inorganic Carbon Dynamics and Sea‐air CO2 Flux

On the basis of field data measured during four cruises from April 2011 to January 2012, spatial and seasonal variations of CO₂ dynamics and aqueous pCO₂ were investigated in the seaweed aquaculture area, Lidao town, China. Results showed that the mean annual concentrations of dissolved inorganic carbon (DIC), HCO₃^?, CO₃^2?, and CO₂ were 2024.79 ± 146.96, 1842.41 ± 132.13, 170.02 ± 42.82, and 12.35 ± 2.52 µmol/L, respectively. There were no significant differences between areas in concentrations of DIC and HCO₃^? (P > 0.05), while the differences for the concentration of CO₂ was very significant (P < 0.01). The mean annual values of aqueous pCO₂ and sea‐air CO₂ flux were 287.80 ± 37.90 µatm and ?32.71 ± 17.23 mmol/m²/d, respectively. There were very significant differences (P < 0.01) for aqueous pCO₂ and sea‐air CO₂ flux not only between different areas, but also between different seasons. The buffer factor β indicates that, inside the seaweed area, inorganic carbon dynamics are mainly influenced by photosynthesis and respiration process.     

Acidified seawater suppresses insulin‐like growth factor I mRNA expression and reduces growth rate of juvenile orange‐spotted groupers,Epinephelus coioides (Hamilton, 1822)

Ocean acidification, resulted from high level of carbon dioxide (CO₂) dissolved in seawater, may disturb the physiology of fish in many ways. However, it is unclear how acidification may impact the growth rate and/or growth hormones of marine fish. In this study, we exposed juvenile orange‐spotted groupers (Epinephelus coioides) to seawater of different levels of acidification: a condition predicted by the Intergovernmental Panel on Climate Change (pH 7.8–8.0), and a more extreme condition (pH 7.4–7.6) that may occur in coastal waters in the near future. After 6 weeks of exposure, the growth rates of fish in pH 7.4–7.6 were less than those raised in control water (pH 8.1–8.3). Furthermore, exposure at pH 7.4–7.6 increased blood pCO₂ and HCO₃^? significantly; exposure at pH 7.8–8.0, meanwhile, did not affect acid–base chemistry. Moreover, exposure to pH 7.4–7.6 resulted in lower levels of hepatic igf1 (insulin‐like growth factor I) mRNA, but did not affect levels of pituitary gh (growth hormone) or hypothalamus psst2 and psst3 (prepro‐somatostatin II and III). The results show that highly acidified seawater suppresses growth of juvenile grouper, which may be a consequence of reduced levels of IGF‐1, but not due to diminished growth hormone release.     

A novel use of social media to evaluate the occurrence of skin lesions affecting wild dusky grouper,Epinephelus marginatus (Lowe, 1834), in Libyan coastal waters

The social media network Facebook^? was used to gather information on the occurrence and geographical distribution of dusky grouper dermatitis, a skin lesion affecting the dusky grouper, Epinephelus marginatus. Dusky grouper are common targets for spear fishermen in the Mediterranean and by monitoring spearfishing activity in Libyan waters, it was possible to document skin lesions from their entries on Facebook. Thirty‐two Facebook accounts and 8 Facebook groups posting from 23 Libyan coastal cities provided a retrospective observational data set comprising a total of 382 images of dusky grouper caught by spearfishing between December 2011 and December 2015. Skin lesions were observable on 57/362 fish, for which images were of sufficient quality for analysis, giving a minimal prevalence for lesions of 15.75%. Only dusky grouper exceeding an estimated 40 cm total length exhibited lesions. The ability to collect useful data about the occurrence and geographical distribution of pathological conditions affecting wild fish using social media networks demonstrates their potential utility as a tool to support epidemiological studies and monitor the health of populations of aquatic animals. To our knowledge, this represents the first time that such an approach has been applied for assessing health in a wild population of fish.     

Water quality and physiological response of F1 hybrid seabream (Pagrus major♀ × Acanthopagrus schlegelii♂) to transport stress at different densities

Hybrid seabream (Pagrus major♀ × Acanthopagrus schlegelii♂) grow quickly, with retarded gonadal growth and enhanced muscle nutritional composition. This F₁ hybrid seabream is a new marine aquaculture fish in China. However, the response of hybrid seabream to transport is severe, which seriously restricts its promotion and development. Water quality and the physiological response of hybrid sea bream were studied at three fish transport densities (5, 10 and 20 g/L) during 8 hr of transport in a light van (60 km hr^?1 and 25°C water temperature). We found that total ammonia–nitrogen and nitrite–nitrogen levels in the water of the highest density group increased sharply after 4 and 8 hr of transport. Cumulative survival of the fish in the 10 and 20 g/L groups (86.7% and 75% respectively) was significantly lower than in the 5 g/L group (100%) after 8 hr of transport (p < .05). Serum cortisol and lactate levels were significantly higher after transport than pre‐stress levels, whereas the glucose level decreased significantly (p < .05). Hepatic triglyceride and glycogen levels and superoxide dismutase and catalase activities were significantly lower in the 20 g/L group than in the 5 g/L group (p < .05). The results show that high‐density transport increased ammonia–nitrogen and nitrite–nitrogen levels in the water as well as cortisol secretion and anaerobic metabolism in the F₁ hybrid seabream, suggesting that total cholesterol and glycogen may be used to supply the energy demand and increased oxidative stress. These results will help to optimize the transport conditions for cultured hybrid seabream.     

Physiological and morphological effects of severe hypoxia,hypoxia and hyperoxia in juvenile turbot (Scophthalmus maximus L.)

We studied the physiological status of juvenile turbot (Scophthalmus maximus L.) under severe hypoxia (1 and 2 mg/L dissolved oxygen, DO), hypoxia (3 and 5 mg/L DO), hyperoxia (11 and 14 mg/L DO) and normoxia (7 mg/L DO, control) conditions. The respiratory rates, haematology parameters, acid–base balance status and gill structure were analysed to find the effects of different DO concentration on turbot. Fish mortality was only observed under severe hypoxia conditions. Severe hypoxia caused an increase in respiratory rates and red blood cell counts, as well as an increase in haemoglobin and haematocrit levels in the fish. In fish exposed to hypoxia conditions, the respiratory rate increased overall as the DO concentration decreased. Lower pCO₂ and HCO₃^? levels led to a high blood pH, while the pO₂ remained stable. In hyperoxia groups, respiratory rate decreased as the DO concentration increased. The levels of pCO₂ and HCO₃^? significantly increased (P < 0.05), while the pO₂ level and blood pH did not change obviously. The gill structure was damaged after prolonged exposure to hyperoxia, but no obvious damage was found in hypoxia groups. The fish that survived the hypoxia or hyperoxia treatment were able to restore the structural integrity of the gills after 14 days' recovery. The results suggest that juvenile turbots can tolerate a wide range of DO concentrations. However, even mild hyperoxia condition (11 mg/L DO), which is widely used in fish culture, has adverse effects on juvenile turbot physiology.     

Pre-sedation and transport of <Emphasis Type="Italic">Rhamdia quelen</Emphasis> in water containing essential oil of <Emphasis Type="Italic">Lippia alba</Emphasis>: metabolic and physiological responses

The effects of transporting silver catfish (Rhamdia quelen) for 6 h in plastic bags containing 0 (control), 30 or 40 µL/L of essential oil (EO) from Lippia alba leaves were investigated. Prior to transport, the fish in the two experimental groups were sedated with 200 µL/L of EO for 3 min. After transport, dissolved oxygen, carbon dioxide, alkalinity, water hardness, pH, temperature and un-ionized ammonia levels in the transport water did not differ significantly among the groups. However, total ammonia nitrogen levels and net Na⁺, Cl^? and K⁺ effluxes were significantly lower in the groups transported with EO of L. alba than those in the control group. PvO₂, PvCO₂ and HCO₃ ^? were higher after transporting fish in 40 µL/L of EO of L. alba, but there were no significant differences between groups regarding blood pH or hematocrit. Cortisol levels were significantly higher in fish transported in 30 µL/L of EO of L. alba compared to those of the control group. The metabolic parameters (glycogen, lactate, total amino acid, total ammonia and total protein) showed different responses after adding EO to the transport water. In conclusion, while the EO of L. alba is recommended for fish transport in the conditions tested in the present study because it was effective in reducing waterborne total ammonia levels and net ion loss, the higher hepatic oxidative stress in this species with the same EO concentrations reported by a previous study led us to conclude that the 10–20 µL/L concentration range of EO and lack of pre-sedation before transport are more effective.     

Efficacy of 17 α‐methyl testosterone and letrozole on sex reversal of protogynous grouper,Epinephelus tauvina (Forskal, 1775) and spawning performance of sex‐reversed males

This study aimed to test the efficacy of 17 α‐methyl testosterone (17 α‐MT) alone and in combination with letrozole, an aromatase inhibitor, for the induction of sex reversal in protogynous greasy grouper, Epinephelus tauvina. Further, the long‐lasting effects of these treatments and spawning performance of sex‐reversed males were also investigated. Greasy grouper with oocytes in the perinucleolus stage were implanted with 5 mg 17 α‐MT kg^?1 body weight (T₁), 5 mg 17 α‐MT and 0.2 mg letrozole kg^?1 body weight (T₂) and 5 mg 17 α‐MT with 0.4 mg letrozole kg^?1 body weight (T₃) and no androgens/enzyme inhibitor implanted (C). The 17 α‐MT alone and in combination of letrozole‐induced sex reversal in greasy grouper, whereas untreated control fish (C) showed normal ovarian development. However, T₂ and T₃ group showed 100% sex reversal and completion of spermatogenesis up to functional male phase in 2 and 3 months, respectively, whereas T₁ group resulted in only 66.67% functional male with motile spermatozoa after 4 months. Sex‐reversed males successfully fertilized the eggs during induced spawning. There were significant differences on fertilization and hatching rates between T₂ group (79.00 ± 4.36%; 77.67 ± 2.87%, respectively) and T₁ group (57.67 ± 3.17%; 63.87 ± 2.91%, respectively). The result suggested that 17 α‐MT (5.0 mg kg^?1 BW) in combination with letrozole (0.2 mg kg^?1 BW) has the potential to produce 100% sex‐reversed male in short period in greasy grouper, which might greatly help in seed production of greasy grouper.     

Does Amia Calva aestivate?

During gradual air exposure, Amia calva show no reduction in oxygen consumption, no increase in plasma urea levels or in urea excretion. Blood pH remains constant, and plasma total CO₂, P_{CO 2}, HCO₃ ^-. total ammonia and NH₃ concentrations all rise significantly. Exposure to 923 μmol/l NH₄Cl does not elicit an increase in urea production or airbreathing. Aquatic hypoxia without access to air does not cause a reduction in aerobic metabolism, and moderate levels result in death. These results suggest that Amia are incapable of aestivation, due to an inability to detoxify ammonia to urea and reduce metabolism, and die following three to five days of air exposure.     

Effectiveness of eugenol sedation to reduce the metabolic rates of cool and warm water fish at high loading densities

Effects of eugenol (AQUI‐S^®20E, 10% active eugenol) sedation on cool water, yellow perch Perca flavescens (Mitchill), and warm water, Nile tilapia Oreochromis niloticus L. fish metabolic rates were assessed. Both species were exposed to 0, 10, 20 and 30 mg L^?1 eugenol using static respirometry. In 17°C water and loading densities of 60, 120 and 240 g L^?1, yellow perch controls (0 mg L^?1 eugenol) had metabolic rates of 329.6–400.0 mg O₂ kg^?1 h^?1, while yellow perch exposed to 20 and 30 mg L^?1 eugenol had significantly reduced metabolic rates of 258.4–325.6 and 189.1–271.0 mg O₂ kg^?1 h^?1 respectively. Nile tilapia exposed to 30 mg L^?1 eugenol had a significantly reduced metabolic rate (424.5 ± 42.3 mg O₂ kg^?1 h^?1) relative to the 0 mg L^?1 eugenol control (546.6 ± 53.5 mg O₂ kg^?1 h^?1) at a loading density of 120 g L^?1 in 22°C water. No significant differences in metabolic rates for Nile tilapia were found at 240 or 360 g L^?1 loading densities when exposed to eugenol. Results suggest that eugenol sedation may benefit yellow perch welfare at high densities (e.g. live transport) due to a reduction in metabolic rates, while further research is needed to assess the benefits of eugenol sedation on Nile tilapia at high loading densities.     

Role of salinity in the dissolution rates of CaCO3 and its implications for aquaculture liming

This work aimed at assessing the role of salinity in the dissolution rates of CaCO₃, discussing its implications for aquaculture liming. A simplified formula of artificial seawater without HCO₃^? was initially prepared. Four batches of 10 L of diluted artificial seawater (salinity = 3.3 g/L) without HCO₃^? were prepared. Sixteen Erlenmeyer flasks were filled up with 2 L each of the diluted artificial seawater without HCO₃^?. Besides, 16 other 2,000‐ml Erlenmeyer flasks were filled up with 2 L of distilled water (freshwater). The experimental treatments were formed by applying increasing amounts of analytical‐grade sodium bicarbonate (NaHCO₃) upon brackish water and freshwater. Accordingly, four initial levels of total alkalinity (TA) have been set up as follows: 4–6, 33–35, 62–63 and 120–122 mg/L. Next, approximately one gram of analytical‐grade calcium carbonate (CaCO₃) was applied onto each flask. Water's pH, TA and calcium concentration were determined weekly over a 7‐week period, by appropriate methods. For a same initial TA, TA increase over time after CaCO₃ application was lower in the brackish water flasks than in the freshwater ones. This was especially clear for moderate (63 mg/L) and high (120 mg/L) alkalinities. It was concluded that brackish and saline waters used for aquaculture would only benefit from CaCO₃ liming if their alkalinities were lower than 60–80 mg/L.     

Intestinal HCO3− secretion in marine teleost fish: evidence for an apical rather than a basolateral Cl−/HCO3− exchanger

Intestinal fluid was collected from 11 marine teleost fish from the Baltic sea and the Pacific ocean. The anterior, mid and posterior segments of the intestine contained 33–110 mM of HCO₃ ^– equivalents (with exception of the Atlantic cod which contained only 5–15 mM). Considering literature values of transepithelial potentials and concentration gradients, these high levels of HCO₃ ^– equivalents are probably the result of active HCO₃ ^– transport. Possible HCO₃ ^– transport mechanisms were studied in the Pacific sanddab (Citharichthys sordidus) in vitro. Measurements of net secretion of HCO₃ ^– equivalents across the intestinal epithelium revealed mucosal DIDS sensitivity (10^–4 M) and Cl^–-dependence of the HCO₃ ^– equivalent net flux, but no serosal DIDS (10^–4 M) sensitivity. Net Na⁺ uptake was abolished in the absence of Cl^–, but some Cl^– uptake persisted in the absence of Na⁺, at a rate similar to that of net HCO₃ ^– secretion. Anterior, mid and posterior segments of the intestine performed similarly. These observations support the presence of an apical rather than a basolateral Cl^–/HCO₃ ^– exchanger and thus contrast the currently accepted model for intestinal HCO₃ ^– secretion. This apical Cl^–/HCO₃ ^– exchanger alone, however, is not sufficient for maintaining the observed HCO₃ ^– equivalents gradient in vivo. We suggest a coupling of cytosolic carbonic anhydrase, a basolateral proton pump and the apical Cl^–/HCO₃ ^– exchanger to explain the intestinal HCO₃ ^– transport.     

Viral encephalopathy and retinopathy is endemic in wild groupers (genus Epinephelus spp.) of the Algerian coast

This work describes betanodavirus infection in two species of groupers (family Serranidae) from the Algerian coast: the dusky grouper Epinephelus marginatus and the golden grouper Epinephelus costae. At necropsy, characteristic clinical signs, external injuries, clouded eyes and brain congestion, generally associated with viral encephalopathy and retinopathy (VER) infection were observed. The partial sequences of RNA1 and RNA2 from two viral strains were obtained, and the phylogenetic analysis revealed the presence of the red-spotted grouper nervous necrosis virus (RGNNV) genotype closely related to strains previously detected in groupers in the same geographic area. Results obtained in this study support the hypothesis that VER disease is endemic in the Algerian grouper population.     

Global population genetic structure of the sequential hermaphrodite,dusky grouper (Epinephelus marginatus)

1. The dusky grouper Epinephelus marginatus is a large epinephelid species that occurs in the eastern and south-western Atlantic and western Indian Oceans. Late maturity, protogynous hermaphroditism, site fidelity, and overfishing have all contributed to its demographic decline.
2. Connectivity and demography within a broad sampling of dusky grouper populations throughout its distribution were assessed. To do so, genetic variation at 11 polymorphic microsatellite loci and a partial sequence of the mitochondrial control region (mtCR) were evaluated.
3. Two major mtCR lineages with a sequence divergence of 1.6% were found. The magnitude of genetic differentiation for mtCR among north and south Atlantic and Indian Ocean populations was high, with Φ_ST = 0.528.
4. D_EST and results of discriminant analysis of principal component revealed significant microsatellite genetic differentiation between all collection areas. Significant pairwise D_EST showed moderate (0.084) to very great (0.603) differentiation. The effective population size was low for all localities, ranging between 25 (Azores Archipelago) and 311 (Rio Grande do Sul). The overall effective population size was estimated as 299 (confidence interval = 215–412), and there was no evidence of strong or recent bottleneck effects.
5. Local and regional genetic structuring among dusky grouper populations is the consequence of the species' site fidelity, distribution across multiple oceanographic boundaries, and probably also of sequential hermaphroditism that contributes to the intensity of random genetic drift.
6. The spatial pattern of genetic structuring of dusky groupers is such that fisheries management and conservation of population genetic integrity will have to be pursued at the local and regional scales.

     

Pharmacokinetics of florfenicol and behaviour of its metabolite florfenicol amine in orange‐spotted grouper (Epinephelus coioides) after oral administration

Pharmacokinetics and elimination of florfenicol and florfenicol amine in grouper held in sea water at 23.3 ± 0.8 °C were studied using HPLC method after they were given a single peroral dose of florfenicol at 24 mg kg^?1 body weight. Florfenicol was rapidly absorbed from intestine and distributed extensively to all the tissues examined. The maximum concentrations (C_max, μg g^?1 or μg mL^?1) in plasma and tissues were observed at 2–6 h (the time to reach maximum concentration, T_max) except for bile (T_max = 24 h) and were in the order of intestine (52.02 ± 25.07) > bile (49.41 ± 28.16) > gill (45.12 ± 11.10) > plasma (28.28 ± 5.43) > liver (21.97 ± 12.08) > muscle (21.63 ± 6.12) > kidney (20.88 ± 11.28) > skin (19.10 ± 5.88). The drug distribution level was higher in plasma than in extravascular tissues except for bile, based on the ratios of the area under concentration–time curve between tissue and plasma (AUC_{tissue/plasma}). The elimination of florfenicol was rapid in fish, and the corresponding half‐lives (T_1/2β) in the order of magnitude were bile (13.92 h) > muscle or liver (12.31 h) > skin (11.77 h) > plasma (11.57) > gill (11.04 h) > intestine (10.55 h) > kidney (10.05 h). The delayed T_max, lower C_max and longer T_1/2β for florfenicol amine compared with florfenicol were measured in grouper.     

Lack of arterial PO<Subscript>2</Subscript> downregulation in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) during long-term normoxia and hyperoxia

Regulation of arterial partial pressure of O₂ (P_aO₂) in Atlantic salmon (Salmo salar) was investigated during resting conditions in normoxic and hyperoxic water. Dorsal aorta cannulated adult Atlantic salmon (1.2–1.6 kg, n = 8) were exposed to 2 week sequential periods of normoxia [16.7 ± 1.1 kPa (mean ± SD)] and hyperoxia (34.1 ± 4.9 kPa) in individual tanks containing seawater (33.7 ± 0.2 ppt) at stable temperature conditions (8.7 ± 0.7°C) and a light regime of L:D = 12:12. Tank design and sampling procedures were optimized to provide suitable shelter and current for the fish, and to allow repeated, undisturbed sampling of blood from free-swimming fish. Fish were sampled regularly through the experimental period. P_wO₂, P_aO₂, blood ion composition (Na⁺, K⁺, Cl⁻), acid–base status (pH, PCO₂, HCO₃ ⁻), haematocrit and glucose were measured. The most frequently observed P_aO₂ values were in the range of 60–80% of P_wO₂, both during normoxia and hyperoxia, and P_aO₂ values were significantly lower during normoxia than during hyperoxia. Blood pH, PCO₂ and HCO₃ ⁻ were significantly elevated during hyperoxia, while, Na⁺, Cl⁻ and Hct were significantly lower. K⁺ and glucose showed no significant differences. This study demonstrates a lack P_aO₂ regulation in Atlantic salmon to low partial pressures, in contrast to previous reports for many aquatic gill breathing animals. Both during normoxia and hyperoxia, P_aO₂ reflects P_wO₂, and alterations in external PO₂ consequently result in proportional arterial PO₂ changes. Physiological adaptation to hyperoxia, as illustrated by changes in several blood parameters, does not include down-regulation of P_aO₂ in Atlantic salmon. The lack of P_aO₂ regulation may make Atlantic salmon vulnerable to the oxidative stress caused by increased free radical formation in hyperoxic conditions.     

Long-term separate and combined effects of environmental hypercapnia and hyperoxia in Atlantic salmon (Salmo salar L.) smolts

Atlantic salmon (Salmo salar L.) parr (mean start weight 50 g) were reared in freshwater (FW) and exposed to three levels of oxygen saturation measured in effluent water; control group (93% O₂, LO₂), medium (111% O₂, MO₂) and high (123% O₂, HO₂). Further three groups were exposed to similar water oxygen levels in combination with elevated carbon dioxide levels (17–18 mg L^– 1 CO₂), named LO₂–CO₂, MO₂–CO₂ and HO₂–CO₂, respectively. The experiment was run in duplicate tanks for 42 days, and the fish were subsequently transferred to the same seawater (SW) regime for 45 days for an assessment of post-smolt growth. As a consequence of the CO₂ addition, tank pH levels in the FW period were reduced from 6.7 to 5.9 for the hypercapnia groups compared to for the normcapnia groups. Water temperature in FW ranged between 6.4 and 9.0 °C. Citrate was added to the water to complex labile aluminium.In the CO₂ groups observed ventilation frequencies were significantly increased compared to the control (p < 0.05). This difference declined towards the end of the FW period, suggesting acclimation to elevated CO₂. The degree of oxygenation appeared to contribute to the acclimation as the lowest mean ventilation frequency on day 36 was found in the HO₂–CO₂ group and the highest in the LO₂–CO₂ group. Lower plasma chloride and sodium levels were observed in the CO₂ groups relative to the respective oxygenation groups during the FW period, while plasma chloride and sodium levels were normalised to equal levels for all groups after 44 days in SW. No significant differences were found among treatments for blood concentrations of red blood cells, haemoglobin, potassium and glucose during the experiment.By termination of the FW period, the HO₂ group had significantly higher body weight than all other groups (p < 0.05), with specific growth rate significantly higher than the CO₂ groups (p < 0.05). Further, the condition factor was significantly lower in all the CO₂ groups at the end of the FW period compared to the control and normcapnia groups (p < 0.05). Although variable among replicates, occurrence of nephrocalcinosis was 10 times higher in the hypercapnia groups than in the control and normcapnia groups. Mortality was negligible (< 2.0%) during the trial, and most of the mortality occurred following SW transfer.     

Acute responses of juvenile cobia Rachycentron canadum (Linnaeus 1766) to acid stress

Fish are potentially submitted to water acidification when reared in recirculating aquaculture systems. This study evaluated the responses of juvenile cobia Rachycentron canadum after acute exposure to acid water. Juvenile cobia (12.6 ± 0.5 g; 14.2 ± 0.2 cm) were acutely exposed to four pH levels (7.9 (control), 6.5, 6.0, and 5.5). After 24 h of exposure to different pH values, fish were sampled for physiological and histopathological evaluation. Acid water affected physiological parameters and induced morphological histopathologies on gill and skin of juvenile cobia, and these effects were more conspicuous with decreasing pH values. Acid stress induced blood acidosis in juvenile cobia, coupled to a decrease in bicarbonate (HCO₃^?) and saturated O₂ (sO₂) in fish blood. On the other hand, haematocrit, haemoglobin and glucose concentration increased their values (P < 0.01) comparing to control level. Hyperplasia with completely fusion of secondary lamella was observed in all pH treatments (6.5. 6.0 and 5.5), while telangiectasia and proliferation of chloride cells were present for fish exposed to pH 6.0 and 5.5. In skin hyperplasia and hypertrophy of mucous cells, necrosis of these cells for fish exposed to pH 6.0 and 5.5 was observed. The results of this study demonstrate that acute acid water exposition affected physiology and histopathology in juvenile cobia, especially at pH values below 6.5. Accordingly, particular attention must be given to pH during cobia reared in recirculating aquaculture.     

Effects of dissolved carbon dioxide on energy metabolism and stress responses in European seabass (Dicentrarchus labrax)

Elevated carbon dioxide concentrations reduce feed intake and growth in several fish species and induce stress responses. In this study, the effects of moderately elevated CO₂ levels on performance, energy partitioning, swimming activity and stress response in European seabass were assessed. European seabass (140.0 g) were reared under two levels of CO₂ (1.6 and 7.0 mg L^?1) and two feeding levels (FLs) (maintenance and satiation) for 60 days, and fish swimming speed was recorded. At the end of the experiment, fish were subjected to an acute stress test. Blood cortisol, glucose and lactate were analysed. Energy and nitrogen balances were quantified based on measurements of body composition and digestibility coefficients. Moderately elevated chronic CO₂ level did neither affect energy requirements for maintenance nor the utilization of digestible energy for growth. However, swimming activity data suggests that FL dependent alterations in energy partitioning took place. Blood cortisol values after the acute stress were affected by additional CO₂ exposure and this effect was also dependent on FL. The elevated CO₂ exposure of 7.0 mg L^?1 appears to act as a chronic stressor as adaptive responses took place, however, this CO₂ exposure seems to be still within the allostatic load of the fish.     

Histological alterations in gills of shrimp Litopenaeus vannamei in low‐salinity waters under different stocking densities: Potential relationship with nitrogen compounds

Two experimental modules with different stocking densities (M1 = 70 and M2 = 120 shrimp /m²) were examined weekly over a culture cycle in tanks with low‐salinity water (1.9 g/L) and zero water exchange. Results showed survival rates of 87.7 and 11.9% in M1 and M2, respectively. Water temperature, pH, dissolved oxygen, electrical conductivity and chlorophyll a were not significantly (p > .05) different between modules. In contrast, the concentrations of nitrogen compounds were significantly (p < .05) different between modules, except nitrite‐N (M2 were 2.31 ± 1.38 mg/L N‐TAN, 0.18 ± 0.49 mg/L N‐NO₂^? and 6.83 ± 6.52 mg/L N‐NO₃^?; in M1: 0.97 ± 0.73 mg/L N‐TAN, 0.05 ± 0.21 mg/L N‐NO₂^? and 0.63 ± 0.70 mg/L N‐NO₃^?). When waters of both modules reached higher levels of ammonia and nitrite, histological alterations were observed in gills. The histological alterations index (HAI) was higher in M2 (5‐112) than in M1 (2‐22).     

Ulcerative dermatitis in wild dusky grouper Epinephelus marginatus (Lowe) from Libyan waters

In the period 2013–2015, wild dusky grouper, Epinephelus marginatus (Lowe), caught in Libyan coastal waters and ranging in size from 42 to 92 cm in total length, were observed to have distinctive skin lesions of unknown aetiology. Histopathologically, the lesions comprised a multifocal, unilateral or bilateral dermatitis, involving the epidermis, superficial dermis and scale pockets, and sometimes, in severe cases, the hypodermis. Severe lesions had marked epidermal spongiosis progressing to ulceration. Healing was observed in some fish. Bacteria and fungi could be isolated from severe lesions, although they were not seen histopathologically in early‐stage lesions. By contrast, metazoan parasite eggs were observed in the dermis and epidermis of some fish with mild and moderate dermatitis. Unidentified gravid digenean trematode parasites carrying similar eggs were also seen within the blood vessels of the deep and superficial dermis. The cause of this distinctive condition, termed dusky grouper dermatitis (DGD), and its potential impact upon already threatened Mediterranean wild dusky grouper populations and upon cultured grouper more widely have yet to be established.