Fish-farming water quality and environmental concerns in Argentina: a regional approach

In spite of the steady increase in fish farming in Argentina, studies on water quality are scarce. Eight fish farms from two different regions in the northeast and east of Argentina were studied to explore source and effluent water quality. Ammonium (NH₄ ⁺), nitrate (NO₃ ⁻), and nitrite (NO₂ ⁻) levels were measured. High nitrate concentrations in water source were observed in the eastern region farms. An increase in NH₄ ⁺, NO₃ ⁻, and NO₂ ⁻ in effluent water was determined in most of the sampled farms. Heavy metals (i.e., cadmium, chromium, copper, iron, manganese, nickel, and zinc) and arsenic concentrations were analyzed. Heavy metal concentrations were below the detection limit in the northern region. However, As was detected in the water source of five farms and was over the recommended limit (100 μgl⁻¹) for aquaculture in one. An increase in Mn and Zn concentrations in effluent water was observed in two farms. The lack of treatment of the effluent water in these farms leads to an increase of nutrients and heavy metal concentrations in the surrounding areas. Environmental effects of fish-farming practices in Argentina are discussed.     

Secondary Stress Responses in Juvenile Brazilian Flounder,Paralichthys orbignyanus,throughout and after Exposure to Sublethal Levels of Ammonia and Nitrite

This study investigated the secondary stress responses of Paralichthys orbignyanus exposed to ammonia and nitrite and after recovery. Fish were exposed to 0.12, 0.28, and 0.57 mg NH₃‐N/L, or 5.72, 10.43, and 15.27 mg NO₂‐N/L for 10 d followed by the same time length for recovery. Ammonia‐ and nitrite‐free water was used as a control treatment. Blood samples were collected after 1, 5, and 10 d of exposure and after recovery. Fish exposed to ammonia presented lower and higher glucose levels after 10 d of exposure and recovery, respectively. Ammonia induced initial and transient ionic disturbances and metabolic alkalosis. Nitrite exposure caused hyperglycemia, increased plasma K⁺ levels, and respiratory alkalosis, whereas metabolic acidosis was observed after recovery. Increased proportion of monocytes and/or granulocytes and reduced number of lymphocytes were demonstrated in fish exposed to 0.28 mg NH₃‐N/L (Day 1) and 10.43 mg NO₂‐N/L (Day 5) and after recovery in the 0.28 and 0.57 mg NH₃‐N/L treatments. Exposure to ammonia decreased the proportion of granulocytes on Day 5. In conclusion, exposure to concentrations at 0.12 mg NH₃‐N/L and 5.72 mg NO₂‐N/L provoked physiological disorders in Brazilian flounder. Nonetheless, fish exposed to 5.72 mg NO₂‐N/L following a 10‐d recovery period showed complete resumption of homeostasis.     

The effect of feeding on oxygen consumption and ammonia excretion of juvenile tench Tinca tinca (L.) reared in a water recirculating system

The effect of feeding frequency (one, three, and continuous feeding), feed ration (0.2, 0.5, 0.8% of total fish biomass), and feeding per se on the oxygen consumption (OC, mg O₂ kg⁻¹ h⁻¹) and ammonia excretion (AE, mg TAN kg⁻¹ h⁻¹) of juvenile tench (body weight 15–19 g) and variations in these parameters in daily cycles were examined. Fish metabolism was studied in a recirculating system (rearing tanks of 0.2 m³, water temperature 23 °C). It was found that oxygen consumption and ammonia excretion depended significantly on feed ration. An increase of feed ration from 0.2 to 0.8% of fish biomass caused an increase of OC and AE from 126.80 mg O₂ kg⁻¹ h⁻¹ and 1.95 mg TAN kg⁻¹ h⁻¹ to 187.35 mg O₂ kg⁻¹ h⁻¹ and 8.80 mg TAN kg⁻¹ h⁻¹ (p<0.05). There was no dependence between feeding frequency and the mean rate of oxygen consumption. However, the relationship between feeding frequency and ammonia excretion by juvenile tench was statistically significant (p<0.05). Feeding frequency significantly affected daily fluctuations of AE and OC. It was found that diurnal variations in metabolic rates were strictly related to tench feeding, and the daily variations of AE were significantly higher than OC.     

Effect of long-term administration of dietary β-1,3-glucan on growth, physiological, and immune responses in Litopenaeus vannamei (Boone, 1931)

β-1,3-Glucan at different dietary doses was administered to enhance the growth, immunity, and survival against nitrite stress in Pacific white shrimp, Litopenaeus vannamei. Four different diets supplemented with 0, 250, 500, or 1,000 mg of β-1,3-glucan kg⁻¹ diets were fed to L. vannamei. Growth performance (weight gain and survival rate), physiological conditions (blood total protein, glucose, lactate, triacylglycerols, cholesterol levels) and immunological responses (superoxide dismutase, catalase, lysozyme, acid phosphatase, and alkaline phosphatase activities) of shrimp were recorded after 84-day feeding and 120 h after exposed to nitrite-N. After 84-day feeding, 250 mg kg⁻¹ β-1,3-glucan diet resulted in better weight gain (P < 0.05). Before the nitrite stress, blood lactate, triacylglycerols, and cholesterol level in shrimp fed with 250 mg kg⁻¹ β-1,3-glucan diet were significantly higher than those observed in shrimp fed with other diets (P < 0.05). Higher activities of catalase, lysozyme, and alkaline phosphatase were observed in shrimp fed with 500 or 1,000 mg kg⁻¹ β-1,3-glucan diet as compared to those obtained in shrimp fed with other diets (P < 0.05). After 120-h nitrite stress, blood protein, lactate, superoxide dismutase, catalase, and alkaline phosphatase activities in shrimp fed with 500 or 1,000 mg kg⁻¹ β-1,3-glucan were significantly higher than those observed in shrimp fed with other diets (P < 0.05). Glucose and triacylglycerol levels of shrimp fed with 500 or 1,000 mg kg⁻¹ β-1,3-glucan were significantly lower than those observed in other diets (P < 0.05). In shrimp fed with 500 and 1,000 mg kg⁻¹ β-1,3-glucan and 120-h after nitrite stress, the mortality was significantly lower than that observed in shrimp of control. Together, in this 84-day feeding trial, 250 mg kg⁻¹ β-1,3-glucan improved growth, whereas 500 mg kg⁻¹ β-1,3-glucan preferentially improved nitrite resistance, probably through accelerating energy metabolism and activating immune system.     

Acute toxicity of ammonia on juvenile cobia (Rachycentron canadum, Linnaeus, 1766) according to the salinity

Juvenile cobia (Rachycentron canadum) (total length 15.16 ± 0.92 cm and weight 19.26 ± 4.5 g) were exposed to different concentrations of ammonia–N (unionized plus ionized ammonia as nitrogen), using the static renewal method at different salinity levels of 5, 20, and 35‰ at pH 8.1 and 25°C. The 24, 48, 72, 96 h LC₅₀ values of ammonia–N for R. canadum juveniles were 60.28, 48.57, 37.42, 22.73 mg l⁻¹ at 35‰; 51.25, 43.63, 28.17, 19.05 mg l⁻¹ at 20‰; and 39.48, 25.31, 19.50, 8.13 mg l⁻¹ at 5‰, respectively. The 24, 48, 72, 96 h LC₅₀ values of NH₃–N (unionized ammonia as nitrogen) were 1.81, 1.46, 1.12, and 0.68 mg l⁻¹ at 35‰; 1.75, 1.49, 0.96, and 0.65 mg l⁻¹ at 20‰; and 1.52, 0.97, 0.71, and 0.31 mg l⁻¹ at 5‰, respectively. As the salinity decreased from 35 to 5‰, susceptibility of ammonia–N increased by 34.5, 47.88, 50.56, and 64.23% after 24, 48, 72, and 96 h exposure, respectively. Furthermore, we found that exposure of fish to ammonia–N caused an increase in oxygen consumption of 129.1, 157.5, and 192% and a decrease in the ammonia excretion level of 53.4, 38.2, and 23.3% with respect to the control.     

Use of acceleration loggers in aquaculture to determine net-cage use and field metabolic rates in red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

We investigated the usefulness of acceleration loggers in aquaculture by examining net-cage use and metabolic rates in red sea bream, Pagrus major. First, the fish’s metabolic rate (mg O₂ kg⁻¹ min⁻¹) was measured with the logger in a swim tunnel at designated water velocities. We found that metabolic rate could be expressed by using a linear regression model of the activity rate index (unitless min⁻¹) derived from acceleration data. Using this equation, the field metabolic rates of three fish in a net cage were monitored and were estimated at 14.1–15.0 kcal kg⁻¹ day⁻¹. The results suggested that 15–19% of energy from satiation feeding ration was consumed for metabolism and activity in the net cage. The loggers showed orderly net-cage use by the fish. Tagged individuals used the whole cage from surface to bottom, but individual fish that preferred the surface area rarely used the bottom, and vice versa. Metabolic rate increased significantly with distance of the fish from their preferred depths. The logger provided information on the physiological and behavioral responses of fish in a given breeding system, and its use should contribute to the design of practical aquaculture systems.     

Enhancement of <Emphasis Type="Italic">Penaeus monodon</Emphasis> shrimp postlarvae growth and survival without water exchange using marine <Emphasis Type="Italic">Bacillus pumilus</Emphasis> and periphytic microalgae

We have investigated the possibility of using a consortium of marine bacterium and periphytic microalgae to improve the water quality and increase the growth and survival of the shrimp Penaeus monodon in a hatchery system. Three treatments were evaluated for their effect on P. monodon postlarvae (PL) when the culture water was not changed: Bacillus pumilus alone (B); periphytic microalgae alone (M); B. pumilus + periphytic microalgae (BM). P. monodon PL raised in a tank of unchanged water without bacterium and periphytic microalgae served as the control. The water in tanks of the M and BM treatments had significantly low levels of total ammonia-nitrogen (TAN) (0.03 and 0.01 mg l⁻¹, respectively) and nitrite-nitrogen (NO₂-N) (0.03, 0.01 mg l⁻¹, respectively) than that in the B (TAN 0.80, NO₂-N 0.68 mg l⁻¹) and control (TAN 1.11, NO₂-N 1.12 mg l⁻¹) tanks. Moreover, PL cultured in tanks M and BM had significantly higher survival and specific growth rates and a significantly higher resistance to the reverse salinity stress test than those in the B and control tanks. Compared to the control PL, the PL cultured in the BM tanks had significantly higher levels of protein, lipid, polyunsaturated fatty acids, ecosapentaenoic acid, and docosahexaenoic acid. The culture water in tanks BM also contained significantly less Vibrio than the control water. Our results illustrate the beneficial effects of a B. pumilus and periphytic microalgae consortium on improving the water quality and the growth and survival of shrimp PL grown in a hatchery system.     

Ammonia and nitrite toxicity to false clownfish <Emphasis Type="Italic">Amphiprion ocellaris</Emphasis>

False clownfish, Amphiprion ocellaris, is one of the most commercialized fish species in the world, highly produced to supply the aquarium market. The high stocking densities used to maximize fish production can increase ammonia and nitrite to toxic levels. In this study, A. ocellaris juveniles (1.20 ± 0.34 g) were exposed to six concentrations of ammonia ranged from 0.23 to 1.63 mg/L NH₃-N and eight concentrations of nitrite (26.3–202.2 mg/L NO₂ ^?-N). The LC₅₀- 24, LC₅₀-48, LC₅₀-72 and LC₅₀-96 h were estimated to be 1.06, 0.83, 0.75 and 0.75 mg/L for NH₃-N and 188.3, 151.01, 124.1 and 108.8 mg/L for NO₂ ^?-N. Analysis of gill lesions caused by sublethal concentrations of these nitrogenous compounds showed that both nitrogenous compounds induced tissue lesions such as hyperplasia of epithelium cells, hypertrophy of chloride cells and lamellar lifting to all concentrations tested. However, histopathological alterations were more conspicuous accordingly the increase of ammonia or nitrite in fish exposed to 0.57 mg/L NH₃-N or 100 mg/L NO₂ ^?-N. Based on our results, we recommend to avoid concentrations higher than 0.57 mg/L of NH₃-N and 25 mg/L of NO₂-N in water.     

Acute toxicity of nitrite on tilapia (Oreochromis niloticus) at different external chloride concentrations

Tilapias (Oreochromis niloticus) juveniles (total length 4.9 ± 0.2 cm and weight 1.8 ± 0.2 g) were exposed to several nitrite concentrations (0, 10, 18, 32, 56 and 100 mg l⁻¹) for 96 h, using a semi-static renewal method at chloride levels of 35.0 and 70.0 mg l⁻¹. At the end of the 96-h period, the median lethal concentration (LC₅₀) of nitrite was 28.18 mg l⁻¹ in water with low chloride content (35.0 mg l⁻¹) and 44.67 mg l⁻¹ with high chloride content (70.0 mg l⁻¹, respectively). It indicated that high concentrations of chloride ions could reduce the toxicity of nitrite. During the toxicity experiments, the behaviour and clinical signs of tilapias were also observed. Furthermore, the test of toxic mechanism was designed taking five test concentrations, viz., 5, 10, 15 and 20 mg l⁻¹ and a nitrite-free control. Nitrite exposure produced high levels of methaemoglobin (MHb) but did not seem to cause mortality, as surviving tilapias showed high levels (85.37 ± 2.23 and 53.82 ± 3.44 at 35.0 and 70.0 mg l⁻¹ chloride, respectively). The percentage of MHb exposed to nitrite was significantly higher (P<0.05) than the control (0 mg l⁻¹ nitrite) and increased with the increasing nitrite concentration. However, the percentage of MHb decreased with the increasing chloride concentration.     

Effects of chronic sub‐lethal nitrite exposure at high water chloride concentration on Atlantic salmon (Salmo salar,Linnaeus 1758) parr

The present study examined the protective effects of water chloride (Cl^?) towards nitrite toxicity in Atlantic salmon parr during 84‐day long nitrite exposure. Effects on growth, histology, blood indices and gene expression were studied at a fixed nominal Cl^? concentration of 200 mg/L and at several water nitrite concentrations (0, 0.5, 2, 5 and 10 mg/L NO₂^?–N). The specific growth rate was significantly reduced during the first three weeks at a Cl:NO₂^?–N ratio of 21:1, suggesting the activation of coping mechanisms at the later stages of the experiment. No significant effect of nitrite on gill histology and mortality was found. Nitrite accumulated in plasma; however, a Cl:NO₂^?–N ratio of 104:1 or higher prevented nitrite entry. The concentration of NO₂^?–N in plasma was significantly reduced at the end of the study, supporting the hypothesis of coping mechanisms. Cystic fibrosis transmembrane conductance regulator (cftr)‐1 showed a significant up‐regulation at highest nitrite concentration on day 22, and in three of the highest exposure groups at the end of the experiment. Our findings suggest that a Cl:NO₂^?–N ratio above 104:1 should be maintained through episodes of nitrite accumulation in water during the production of Atlantic salmon parr.     

Trypsin from the viscera of Bogue (<Emphasis Type="Italic">Boops boops</Emphasis>): isolation and characterisation

Trypsin from the viscera of Bogue (Boops boops) was purified to homogeneity by precipitation with ammonium sulphate, Sephadex G-100 gel filtration and Mono Q-Sepharose anion exchange chromatography, with an 8.5-fold increase in specific activity and 36% recovery. The molecular weight of the purified enzyme was estimated to be 23 kDa by SDS–PAGE and size exclusion chromatography. The purified trypsin appeared as a single band on native-PAGE and zymography staining. The purified enzyme showed esterase-specific activity on N-α-benzoyl-l-arginine ethyl ester (BAEE) and amidase activity on N-α-benzoyl-dl-arginine-p-nitroanilide (BAPNA). The optimum pH and temperature for the enzyme activity, after 10 min incubation, were pH 9.0 and 55°C, respectively, using BAPNA as a substrate. The trypsin kinetic constants K _m and k _cat on BAPNA were 0.13 mM and 1.56 s⁻¹, respectively, while the catalytic efficiency k _cat /K _m was 12 s⁻¹ mM⁻¹. Biochemical characterisation of B. boops trypsin showed that this enzyme can be used as a possible biotechnological tool in the fish processing and food industries.     

Effects of Ambient Nitrite on Amazon River Prawn,Macrobrachium amazonicum,larvae

The effects of nitrite concentration on larval development of Amazon river prawn, Macrobrachium amazonicum, were studied in laboratory. In Experiment 1, larvae were reared in 600‐mL glass beakers filled with 300‐mL water with nitrite concentration of 0, 0.2, 0.4, 0.8 and 1.6 mg/L NO₂‐N. In Experiment 2, total ammonia nitrogen (TAN, NH₃‐N + NH₄‐N) excretion were analyzed in zoea (Z) I, III, VII and IX exposed to 0, 0.4, 0.8 and 1.6 mg/L NO₂‐N. In both experiments each treatment was conducted in five replicates. The experiments were carried out in test solutions at 10 salinity, constant temperature 30 C and 12:12 h daylight : darkness regime. Survival, productivity, weight gain and larval stage index decreased linearly with increasing ambient nitrite concentration. However, there was no significant difference among larvae reared at concentration ranging from 0 to 0.8 mg/L NO₂‐N by ANOVA in all variables. Individual ammonia‐N and mass‐specific ammonia‐N excretion increased in ZI and ZIX, was almost constant in ZIII and decreased in ZVII from 0 to 1.6 mg/L NO₂‐N. The relationship between individual TAN and body mass suggested that 1.6 mg/L NO₂‐N stress the larvae. Despite of the effects of nitrite on larvae follow a dose‐dependent response and shows large variability among individuals, levels below 0.8 mg/L may be used as a general reference in commercial hatcheries, which should be applied carefully.     

Protein and energy utilization and the requirements for maintenance in juvenile mulloway (<Emphasis Type="Italic">Argyrosomus japonicus</Emphasis>)

This study describes the digestible protein (DP) and digestible energy (DE) utilization in juvenile mulloway, and determined the requirements for maintenance. This was achieved by feeding triplicate groups of fish weighing 40 or 129 g held at two temperatures (20 or 26°C), on a commercial diet (21.4 g DP mJ DE⁻¹) at four different ration levels ranging from 0.25% of its initial body weight to apparent satiation over 8 weeks. Weight gain and protein and energy retention increased linearly with increasing feed intake. However, energy retention efficiency (ERE) and protein retention efficiency (PRE) responses were curvilinear with optimal values, depending on fish size, approaching or occurring at satiated feeding levels. Maximum predicted PRE was affected by body size, but not temperature; PRE values were 0.50 and 0.50 for small mulloway, and 0.41 and 0.43 for large mulloway, at 20 and 26°C respectively. ERE demonstrated a similar response, with values of 0.42 and 0.43 for small, and 0.32 and 0.34 for large mulloway at 20 and 26°C respectively. Utilization efficiencies for growth based on linear regression for DP (0.58) and DE (0.60) were independent of fish size and temperature. The partial utilization efficiencies of DE for protein (k _p) and lipid (k _l) deposition estimated using a factorial multiple regression approach were 0.49 and 0.75 respectively. Maintenance requirements estimated using linear regression were independent of temperature for DP (0.47 g DP kg^−0.7 day⁻¹) while maintenance requirements for DE increased with increasing temperature (44.2–49.6 kJ DE kg^−0.8 day⁻¹). Relative feed intake was greatest for small mulloway fed to satiation at 26°C and this corresponded to a greater increase in growth. Large mulloway fed to satiation ate significantly more at 26°C, but did not perform better than the corresponding satiated group held at 20°C. Mulloway should be fed to satiation to maximize growth potential if diets contain 21.4 g DP mJ DE⁻¹.     

Effects of temperature and salinity on oxygen consumption and ammonia excretion of juvenile miiuy croaker, <Emphasis Type="Italic">Miichthys miiuy</Emphasis> (Basilewsky)

The metabolic responses of the juvenile Miichthys miiuy in terms of oxygen consumption and ammonia excretion to changes in temperature (6–25°C) and salinity (16–31 ppt) were investigated. At a constant salinity of 26 ppt, the oxygen consumption rate (OCR) of the fish increased with an increase in temperature and ranged between 133.38 and 594.96 μg O₂ h⁻¹ g⁻¹ DW. The effect of temperature on OCR was significant (P < 0.01). Q₁₀ coefficients were 6.80, 1.41, 1.29 and 2.36 at temperatures of 6–10, 10–15, 15–20 and 20–25°C, respectively, suggesting that the juveniles of M. miiuy will be well adapted to the field temperature in the summer, but not in the winter. The ammonium excretion rates (AER) of the fish were also affected significantly by temperature (P < 0.01). The O:N ratio at temperatures of 6, 10, 15 and 20°C ranged from 13.12 to 20.91, which was indicative of a protein-dominated metabolism, whereas the O:N at a temperature of 25°C was 51.37, suggesting that protein-lipids were used as an energy substrate. At a constant temperature of 15°C, the OCRs of the fish ranged between 334.14 (at 31 ppt) and 409.68 (at 16 ppt) μg O₂ h⁻¹ g⁻¹ DW. No significant differences were observed in the OCR and AER of the juveniles between salinities of 26 and 31 ppt (P > 0.05). The OCR and AER at 16 ppt were, however, significantly higher than those at 26 and 31 ppt (P < 0.05), indicating salinity lower than 16 ppt is presumably stressful to M. miiuy juveniles.     

Dietary polysaccharide from <Emphasis Type="Italic">Angelica sinensis</Emphasis> enhanced cellular defence responses and disease resistance of grouper <Emphasis Type="Italic">Epinephelus malabaricus</Emphasis>

The purpose of this study was to determine the effect of Angelica sinensis polysaccharide (ASP) supplemented in diet on the innate cellular immune response and disease resistance in grouper, Epinephelus malabaricus. Fish were fed diets containing different doses of ASP (0, 500 and 3,000 mg kg⁻¹ diet) for 12 weeks. After 12 week feeding, the respiratory burst activity, phagocytic activity, and leukocytes proliferation in head kidney were assayed. The functional immunity in terms of cumulative mortality was also assessed by a challenge with live Edwardsiella tarda. Results showed that the respiratory burst activities in ASP-supplemented groups were increased significantly. The respiratory burst index was the highest in fish-fed 3000 mg kg⁻¹ diet and the lowest in control. The phagocytic activities in ASP-supplemented groups were significantly higher than that of control. No significant difference in phagocytic activity was observed between ASP-supplemented groups. ASP stimulated the head kidney leukocytes proliferation significantly, despite the absence of lipopolysaccharide (LPS) or not. The cumulative mortalities of fish fed with 3000 mg ASP kg⁻¹ diet were significantly lower than those fed with 500 mg ASP kg⁻¹ diet and control diet after 96 h of challenge. In conclusion, dietary ASP enhanced some cellular immune parameters and disease resistance against E. tarda in grouper.     

Optimum ration level for better growth,conversion efficiencies and body composition of fingerling <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis> (Bloch)

The effects of ration levels on growth, conversion efficiencies and body composition of fingerling Heteropneustes fossilis (6.8 ± 0.04 cm, 5.0 ± 0.02 g) were studied by feeding isonitrogenous (40% crude protein) and isocaloric (19.06 MJ kg⁻¹ gross energy) diets representing 1, 3, 5, 7 and 9% of the body weight (BW) day⁻¹ to triplicate groups of fish . Growth performance of the fish fed at the various ration levels was evaluated on the basis of live weight gain percentage (LWG%), feed conversion ratio (FCR), specific growth rate percentage (SGR%), protein retention efficiency (PRE%) and energy retention efficiency (ERE%) data. Maximum LWG% and SGR were obtained at a feeding rate of 7% BW day⁻¹, whereas best FCR (1.6), PRE% and ERE% were recorded at a feeding rate of 5% BW day⁻¹. Maximum body protein was also obtained for the group receiving the diet representing 5% of their body weight. However, a linear increase in fat content was noted with the increase in ration levels up to 7% BW day⁻¹. The SGR, FCR, PRE and ERE data were also analyzed using second-degree polynomial regression analysis to obtain more precise information on ration level, with the results showing that the optimal ration for these parameters was 6.8, 6.1, 5.9 and 6.2% BW day⁻¹, respectively. Based on the above second-degree polynomial regression analysis, the optimum ration level for better growth, conversion efficiencies and body composition of fingerling H. fossilis was found to be in the range of 5.9–6.8% of the BW day⁻¹, corresponding to 2.36–2.72 g protein and 88.20–101.66 MJ digestible energy kg⁻¹ diet day⁻¹.     

Econometric model of viability/profitability of octopus (<Emphasis Type="Italic">Octopus vulgaris</Emphasis>) ongrowing in sea cages

The interest in diversifying aquacultural production with new species is evident, preferably with species with a high commercial value and whose consumption is not geographically limited. In this sense, octopus would be a good choice. The present work, therefore, presents an economic-financial analysis of the commercial viability of octopus ongrowing in the Mediterranean, paying special attention to the one- or two-cycle approach. Viability–profitability equations are developed for analysing economic parameters associated with production. To estimate the investment, an offshore ongrowing installation was designed comprising 150 cages containing 30,000 individuals. Growth was estimated for the two strategies: (A) Two consecutive cycles per year (2CY), each lasting 3.5 months from October to June. Initial weight was 0.7 kg, and the mean final weight was 2.7 kg. (B) One growth cycle per year (1CY) beginning in November or December and finishing in April or May, starting with the same weight individuals (0.7 kg) and giving individuals with a final weight of 3.65 kg. The highest costs, the most important from an economic point of view, are feed (38.57 and 40.03%, respectively), fixed assets (25.26 and 17.47%, respectively), juveniles (16.65 and 23.02%, respectively), and in fourth place salaries (14.34 and 15.60%, respectively). The equations obtained for the variables NPV (Net Present Value) and IRR (Internal Ratio of Return) are the following: 1 cycle per year (1CY), NPV = −489,088 − 1.45 K − 1,439,823 C _F − 1,477,890 C _J − 1,460,627 C _O + 1,432,386 SP, IRR = 0.1328 − 7.82 × 10⁻⁸ K − 0.0416 C _F − 0.0437 C _J − 0.0427 C _O + 0.0412 SP. 2 cycles per year (2CY), NPV = −404,431 − 1.46 K − 2,118,410 C _F − 2,121,221 C _J − 2,144,755 C _O + 2,129,223 SP, and IRR = 0.0952 − 6.95 × 10⁻⁸ K − 0.0586 C _F − 0.0588 C _J − 0.0588 C _O + 0.0613 SP. The NPV and IRR values estimated with the econometric equations for each option using the initial variables confirm that 1CY has a higher NPV (3,013,569 €) and IRR (12.27%) than 2CY, with an NPV of 2,396,708 € and IRR of 10.39%. In both cases, octopus ongrowing is economically viable, although 1CY is the most favourable system.     

Effects of adding sucrose on Penaeus monodon (Fabricius, 1798) growth performance and water quality in a biofloc system

A 60‐day indoor growth trial was conducted to study the effects of biofloc on the growth performance of a Penaeus monodon (Fabricius, 1798), water quality and biological indicators including biofloc volume, chlorophyll‐a, heterotrophic bacteria and Bacillus quantity. Two concentrations of sucrose (0 and 75%) were added daily to the P. monodon culture systems (2.94 ± 0.11 g), which were conducted indoors in fibre‐glass tanks (500 L). Results showed that the final body weight and weight gain of the adding 75% sucrose group were significantly higher (P < 0.05) than that of the control, as well as significantly (P < 0.05) improved specific growth rates and survival rates, and reduced feed coefficient. Adding 75% sucrose promoted heterotrophic bacteria, Bacillus and phytoplankton reproduction, and significantly (P < 0.05) reduced the concentration of ammonia‐N (NH₄‐N), nitrite‐N (NO₂‐N) and nitrate‐N (NO₃‐N). The changes of water quality indicators in the two groups showed the similar trend at the end of the experiment, and the ammonia‐N, nitrite‐N, nitrate‐N and phosphate‐P concentrations in the 75% sucrose group were significantly (P < 0.05) lower than those of the control group, Chlorophyll‐a concentrations peaked at 389.12 μg/L in the biofloc sucrose group at 18:00 h, and heterotrophic bacteria peaked 8 h after sucrose was added. The addition of sucrose also reduced the pH of the water. Our research showed that adding sucrose promoted biofloc formation and shortened the formation time; increased the number of heterotrophic bacteria and algae which might play a role in improving water quality by assimilating ammonia‐N and other harmful substances in the water; supplemented food for P monodon growth; and reduced the feed coefficient.     

Probiotic bacteria <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> influences the blood profile in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> (Walbaum)

This paper reports the effect of feeding probiotic diets on blood profiles in rainbow trout. Two experiments were performed: in the first, fish of average weight 75 g were offered either a commercial feed or the same incorporated with 10⁹ CFU g⁻¹ of lactic acid bacteria Lactobacillus rhamnosus for 30 days; in the second study performed for a similar duration, fish of average weight 126 g were offered formulated diets that either contained the same bacteria in heat-killed or freeze-dried form (nearly 10¹¹ CFU g⁻¹), or the basal diet without the bacteria. Blood samples were collected at different times after commencement of probiotic feeding to determine the total cholesterol, triglyceride contents, the plasma alkaline phosphatase activity, plasma protein and hematocrit value. The plasma cholesterol significantly increased upon probiotic feeding in the first experiment. A significant elevation (P < 0.05) of plasma cholesterol and triglyceride and alkaline phosphatase activity level was found in the freeze-dried probiotic fed groups at 20 and 30 days postfeeding. This was concomitant with the increased plasma protein and hematocrit values in FD group at 20 and 30 days. Likewise, the heat-killed probiotic fed group registered significantly high values of triglycerides, alkaline phosphatase activity, and plasma protein compared to the control diet fed groups after 20 days of feeding. Thus, alterations in the blood profiles could serve as supplementary information when examining the benefits of probiotics for fish.