Shipping studies with juvenile and adult Malaysian prawns Macrobrachium rosenbergii (de Man)

Four studies examined shipping factors of packing technique, density, duration, type of water and use of habitat material for shipping juvenile and adult prawns Macrobrachium rosenbergii. Prawns were shipped in double polyethylene lined 38 × 38 × 20 cm deep styrofoam boxes containing oxygenated water. At temperatures of 19–20°C, 17 g prawns could be shipped safely for 42 h at a density of 10–12 prawns per box (12–15 g liter⁻¹ shipping water). Juveniles, mean size about 6 g, could be shipped at a density of 40 per box (18 g liter⁻¹) for 24 h or 20–25 per box (9–11 g liter⁻¹) for 48 h. Use of mesh material to increase surface area in the box did not appear beneficial nor did shipping in brackish water (salinity8‰). Adults packed unrestricted resulted in survival rates substantially higher than those obtained from immobilized prawns wrapped in mesh.

During the shipment, pH and dissolved oxygen concentrations decreased whereas ammonia concentrations increased. The decreased pH levels may have reduced the ammonia toxicity by decreasing the amount of toxic unionized ammonia (NH₃) in solution. In general, dissolved oxygen concentrations appeared more closely related to survival rates than did other water quality parameters which were measured.     

Effect of diphenyl diselenide diet supplementation on oxidative stress biomarkers in two species of freshwater fish exposed to the insecticide fipronil

The ability of diphenyl diselenide [(PhSe)₂] to attenuate oxidative damage was evaluated in the liver, gills, brain, and muscle of carp (Cyprinus carpio) and silver catfish (Rhamdia quelen) experimentally exposed to fipronil (FPN). Initially, the fish were fed a diet without (PhSe)₂ or a diet containing 3.0 mg/kg of (PhSe)₂ for 60 days. After the 60-day period, the fish were exposed to 0.65 µg/L of FPN for 192 h. The results showed that carp exposed to FPN and not fed with (PhSe)₂ exhibited acetylcholinesterase (AChE) inhibition in brain and muscle, and increased thiobarbituric acid-reactive substance (TBARS) in liver, gills, and brain. Furthermore, FPN decreased nonprotein thiols (NPSH) and δ-aminolevulinate dehydratase (δ-ALA-D) in carp liver and gills, and increased plasma glucose and protein levels. In silver catfish, FPN inhibited AChE and increased TBARS levels in muscle. In addition, glutathione S-transferase (GST) decreased in liver and muscle, and plasma glucose was increased. (PhSe)₂ reversed some of these effects. It prevented the increase in TBARS levels in liver, gills, and brain in carp and in silver catfish muscle, and reversed the increase in plasma glucose levels in both species. Additionally, (PhSe)₂ increased the NPSH levels in carp and silver catfish that had decreased in response to FPN exposure. However, (PhSe)₂ was not effective in reversing the AChE inhibition in brain and muscle or the δ-ALA-D decrease in carp liver. Thus, (PhSe)₂ protects tissues of both species of fish, mainly by preventing or counteracting the effects of FPN, on TBARS levels, antioxidants, and present anti-hyperglycemic property.     

Studies of limiting factors governing the waterflow requirement for Atlantic salmon (Salmo salar L.) in landbased seawater systems

In the first part of the investigation two different models are derived to obtain the direct ratio between (a) total ammonia and oxygen and (b) unionized ammonia and oxygen as limiting factors for the waterflow requirement for salmonids in landbased seawater systems. In both models the mass related ammonia quotient, expressed as the ratio between total ammonia excreted (mg NH₄---N per kilogramme fish per minute) and oxygen consumed (mg O₂ per kilogramme fish per minute) is an important factor.

The second part of the study reports measurements of the mass related ammonia quotient (diurnal cycles) of Atlantic salmon kept in a landbased tank farm and calculations of waterflow requirements. The total variation find of the mass related ammonia quotient values were between 0·03 and 0·08. Based on two of the most extreme diurnal cycles with respect to temperature and fish size, the specific waterflow requirement applying ammonia as a limiting factor was in the range 0·04–0·17 litres/kg min.

The third part of the study applies the measurements obtained for the ammonia quotient to the models. The results show that un-ionized ammonia may become the first limiting factor by combinations of a high difference in the dissolved oxygen concentration between the inlet water and the discharge, a high pH and a low threshold level for un-ionized ammonia. However, oxygen is usually found to be the first limiting factor when compared to un-ionized ammonia.

If the value 0·5 mg NH₄---N/litre is used as the limiting criterion for total ammonia, the difference in the dissolved oxygen concentration between the inlet water and the discharge should not exceed about 7 mg/litre. However, in seawater oxygenation is necessary to provide and maintain this difference. Therefore both models result in the same conclusion for moderate levels of oxygen addition.     

Effect of dietary vitamin C supplementation on the oxygen consumption, ammonia-N excretion and Na/K ATPase of Macrobrachium nipponense exposed to ambient ammonia

The 96-h LC₅₀ of ammonia-N and the effects of dietary vitamin C on oxygen consumption, ammonia-N excretion and Na⁺/K⁺ ATPase activity of Macrobrachium nipponense exposed to ambient ammonia were investigated. The results showed that the 96-h LC₅₀ of ammonia-N was 36.6 mg l⁻¹ for the freshwater prawn, M. nipponense, at pH 8.0. When prawns were exposed to high ambient ammonia-N concentrations, the oxygen consumption rate increased and ammonia excretion decreased. Dietary vitamin C supplementation led to higher oxygen consumption and lower ammonia excretion. Na⁺/K⁺ ATPase activity increased with increased ambient ammonia-N exposure in the range of 0–18.3 mg l⁻¹, and then was reduced at ambient ammonia-N 36.6 mg l⁻¹. Na⁺/K⁺ ATPase activities of prawns fed a vitamin C-supplemented diet were significantly lower than those of prawns fed a diet which was not supplemented with vitamin C.     

Bioaccumulation of cadmium and its biochemical effect on selected tissues of the catfish (<Emphasis Type="Italic">Clarias gariepinus</Emphasis>)

The present study examines the pattern of accumulation of cadmium (Cd) and its biochemical effects on selected tissues of a variety of African catfish (Clarias gariepinus), after exposure to various doses of Cd. The results obtained indicate that at the end of 21 days of exposure, the total tissue organ cadmium concentration followed the pattern kidney > gill > liver > muscle for each of the exposure concentrations. The levels of Cd in these organs were higher than those in ambient water. Moreover, while the rate of uptake of Cd increased with time in the kidney, liver and muscle, it decreased in the gill. Superoxide dismutase (SOD) was significantly elevated only in the kidney of catfish treated with 0.2 and 0.4 ppm of Cd for 7 days compared with the control. Conversely, gill SOD was significantly decreased in the same concentrations of Cd-treated catfish relative to the control. Statistically similar levels of SOD were observed in the liver, brain and muscle with all the treatments after the same duration of treatment. In the fish exposed for 21 days, SOD activity was significantly decreased in the kidney with a corresponding increase in lipid peroxidation (LPO), but it manifested only with the 0.2- and 0.4-ppm Cd treatment relative to the control. In the liver, however, Cd exposure significantly increased SOD in the 0.2- and 0.4-ppm treatments of the same duration. In conclusion, the present study indicates that the accumulation of Cd and its effect on SOD and LPO in C. gariepinus is dependent on concentration, tissue and time     

Survival of silver catfish fingerlings exposed to acute changes of water pH and hardness

Theaim of this study was to examine the survival of fingerlings of silver catfish,Rhamdia quelen, in water with different pH and hardnessvalues. Fingerlings (1.60 ± 0.14 g; 5.67 ± 0.15cm) were randomly assigned to 35 treatments (in triplicate) andmaintained in 44 L polyethylene tanks (10 fingerlings/tank) for 96h. Fingerlings were exposed to seven solutions of varying pH (3.5,3.75, 4.0, 7.0, 9.5, 10.0, and 10.5) and five solutions of varying hardness(30,70, 150, 300, and 600 mg.l^–1 CaCO₃).Survival was assessed at 12, 24, 48, 72, and 96 h. Fingerlingmortality was 100% after 12 h exposure to pH 3.5 at all hardnesslevels, whereas mortality at pH 3.75, 10.0, and 10.5 decreased with increasinghardness. There was no mortality of fingerlings exposed to pH 4.0, 7.0, and 9.5at all hardness levels. The results allow us to conclude that the hardnesslevels studied do not affect the survival of silver catfish fingerlings exposedto pH 3.5, 4.0, 7.0, and 9.5 for 96 h. However, the increase ofwater hardness improved survival of fingerlings of this species exposed to pH3.75, 10.0, and 10.5.     

Larval Development of the Giant River Prawn Macrobrachium rosenbergii at Different Ammonia Concentrations and pH Values

The effect of ammonia and pH levels on giant river prawn Macrobrachium rosenbergii larvae were evaluated to provide science-based information on safe levels of ammonia and pH for larviculture. Survival rate, developmental stage, and larval weight gain were determined for larvae kept in water with total ammonia (NH ₄-N)concentrations of 0, 1, 2, 4, and 8 mg\L and pH 7, 8, and 9. The trials were conducted in two phases: phase 1, larvae from stages I through VIII and phase 2, larvae from stage VIII until metamorphose. Oxygen consumption was determined for larvae in stages I and VIII at total ammonia concentrations of 0, 4, and 8 mg/L and pH 8. Survival rate up to stage VIII varied from 86 to 98% and did not differ for total ammonia concentrations in pH 7 and 8 and for 0 mg/L NH₄ N in pH 9. Survival rate was significantly lower (0–20%) for total ammonia concentrations from 1 to 8 mg/L (0.43–3.41 mg/L of unionized ammonia) in pH 9. Larval stage indexes (7.9–8.0 range) and weight gain (1.572–2.931 mg range) of larvae at the end of phase 1 of the experiment did not differ for the different ammonia concentration solutions, but were significantly lower in pH 9. In phase 2, no parameter differed among treatments for pH 7 and 8; however there was total mortality at pH 9 until 96h. Respiration rates diminished when larvae were exposed to total ammonia concentrations of 4 and 8 mg/L (0.28 and 0.55 mg/L of unionized ammonia), but development remained unaltered. Therefore, M. rosenbergii larvae tolerate high levels of total ammonia, while toxicity depends primarily on unionized ammonia concentrations. In addition, alkaline pH (9) acted directly on the larvae, curbing development and causing severe mortality. Larval tolerance to high ammonia and pH levels decreases for the last zoeal stages.     

Sublethal effects and safe levels of carbon dioxide in seawater for Atlantic salmon postsmolts (Salmo salar L.): ion regulation and growth

Atlantic salmon (Salmo salar L.) postsmolts (0.17–0.26 kg) were exposed to four different levels of carbon dioxide partial pressure for 43 days in an open flow system: 0.6 mm Hg (control), 4.9 mm Hg (low), 12 mm Hg (medium), and 20 mm Hg (high). The water temperature was 15–16°C and the salinity 34‰. In the low carbon dioxide group (P_CO2=4.9 mm Hg; 10.6 mg/l), no significant differences were found in blood parameters (haematocrit, plasma chloride and plasma sodium) or in growth parameters (weight, length and condition factor) when compared to the control group. After 43 days, the mean plasma chloride concentration for the medium group (P_CO2=12 mm Hg; 26 mg/l) was significantly reduced, while weight and condition factor were slightly, although not significantly, lowered. For the high carbon dioxide group (P_CO2=20 mm Hg; 44 mg/l) plasma sodium and plasma pH were significantly increased and plasma chloride, oxygen consumption, weight, length and condition factor were significantly reduced at the end of exposure. There was no mortality in the control group or in the low carbon dioxide group. The mortalities in the medium and high carbon dioxide groups were 1.1 and 4.3%, respectively. Nephrocalsinosis was not observed in any of the groups. The results of the present investigation indicate that the CO₂ concentration of the low group may represent a safe level for Atlantic salmon postsmolts when the temperature is 15–16°C and the oxygen level is 6–7 mg/l. Further studies are required.     

Effects of Water pH and Hardness on Infection of Silver Catfish,Rhamdia quelen,Fingerlings by Ichthyophthirius multifiliis

The aim of this study is to determine the effect of (1) different pH levels (5, 6, 7, 8, and 9) with water hardness 20 mg/L CaCO₃ and (2) pH 5 and 7 with varying water hardnesses (20, 60, and 120 mg/L CaCO₃) on the intensity of infection by Ichthyophthirius multifiliis in fingerlings of the silver catfish, Rhamdia quelen. In Experiment 1, the lowest and highest mortality rates were observed in fingerlings exposed to pH 5 and 9, respectively; in Experiment 2, fish kept at pH 5 and 7 with hardness 20 mg/L CaCO₃ showed significantly lowest and highest cumulative mortality, respectively, than those maintained in other conditions. The lowest intensity of trophonts/fingerling was observed at pH 5 and hardness 20 mg/L CaCO₃ in both experiments. We conclude that infection by I. multifiliis is less severe in silver catfish maintained at pH 5 and hardness 20 mg/L CaCO₃. High water hardness led to an increased intensity of trophonts and decreased survival in silver catfish kept at pH 5, but decreased intensity of trophonts and improved survival when the fish were kept at pH 7.     

Aloysia triphylla essential oil as food additive for Rhamdia quelen – Stress and antioxidant parameters

We examined the effects of dietary supplementation for 21 days with different levels (0, 0.25 and 2.0 ml/kg) of the Aloysia triphylla essential oil (EOAT) on silver catfish (Rhamdia quelen). Cortisol levels were lower in fish fed EOAT at 2.0 ml/kg diet, and lactate levels were lower in those fed at both doses. Glucose, alanine aminotransferase, aspartate aminotransferase and triglyceride levels did not vary between groups. The biomarkers of oxidative stress, thiobarbituric acid‐reactive substances, lipid hydroperoxide, superoxide dismutase, catalase and non‐protein thiols, were lower in the brain, liver and muscle of fish fed EOAT at 2.0 ml EO/kg diet. Glutathione‐S‐transferase, reduced glutathione, plasma Na⁺, Cl^?, and K⁺, and gill Na⁺/K⁺‐ATPase and H⁺‐ATPase did not vary between groups. Taken together, our results clearly indicate that the addition of EOAT at 2.0 ml/kg diet improves oxidative status and lowers the stress response in silver catfish.     

Antioxidant processes are affected in juvenile rainbow trout (Oncorhynchus mykiss) exposed to ozone and oxygen-supersaturated water

Two groups of juvenile rainbow trout (Oncorhynchus mykiss) were exposed for 4 h to either hyperoxic (>40 mg O₂/l) or ozonised (5.2 μg O₃/l) water containing supersaturated oxygen. Gill, liver, blood cells and plasma were taken 1, 5, 12, 24 and 48 h following the exposure periods and antioxidant responses and oxidative damage studied in terms of, respectively, antioxidant enzyme activities/glutathione status and lipid peroxidation. Observed biochemical changes were significant at p<0.05. Ozonation elevated oxidised glutathione (GSSG) levels, increased lipid peroxidation and decreased reduced glutathione (GSH) levels in gills 1 h following exposure, which indicate oxidative stress. However, the longer-term effects (48 h) following ozone exposure resulted in increased GSH levels in both gills and liver and, measured as oxidative stress index (OSI), were indicative of enhanced potential of tissues to resist oxidative stress. Ozonation also resulted in elevated activity of superoxide dismutase (SOD) at 5–12 h following exposure in gills compared to 24–48 h in liver, indicating either differential regulation and time-courses of response, or an earlier impact of ozonolysis products on gills than liver. In contrast, catalase activity was elevated in both gills and liver at 24 h by the effects of hyperoxia alone. Hyperoxia also decreased GSSG levels in both gills and liver, but had no effect on lipid peroxidation. Increases were seen in the activities of selenium-dependent glutathione peroxidase as a result of ozonation (gills; 5 and 24 h) and hyperoxia (liver; 1 h), and in total GPX (Se-dependent and independent) as a result of ozonation (both tissues; 48 h), but no effects were seen on glutathione reductase (GR) in either tissues. Levels of GSH were increased in blood cells at various times following hyperoxia. Overall, the results show (i) differential antioxidant and pro-oxidant effects of ozonation compared to hyperoxia, (ii) gills and possibly blood as the first line of impact and defence, with later effects on liver, and (iii) that even after 24–48 h following ozone exposure, all antioxidant defences had not returned to pre-exposure values.     

14C-glucose injection in Atlantic cod, Gadus morhua, metabolic responses and excretion via the gill membrane

In the present study cod were separately placed in fish metabolic chambers. Ten individuals were injected with a dose of 1 μCi ¹⁴C-glucose, in addition to 1 g pure glucose per kg live weight, and 10 individuals were kept under the same conditions and sham injected with 9 g L⁻¹ (0.9%) sterile saline solution.
Of the injected ¹⁴C-glucose, 3% was recovered in plasma, 2.9% in liver, 1.7% in red muscle, 18.2% in white muscle, 0.2% in heart, 1.9% in gills and 12.1% in gill-surrounding water. Of the 12.1% in gill-surrounding water, 9.1% was found to be in the form of CO₂, leaving 3% to pure glucose and lactate. These results indicate a relatively high production of CO₂ from glucose showing a utilization for energy, and a possible route of excretion of excess glucose via the gill membrane.
Activity of ¹⁴C-glucose on a concentration basis showed in descending order the following organs to be metabolically active in glucose utilization: gills > plasma (as a transporter) > heart > red muscle > liver > white muscle.
Of the total amount of ¹⁴C-glucose injected, only 0.3% was recovered in the liver lipid fraction, and mainly as triacylglyceroles; minor ¹⁴C-activity was found in mono- and diacylglyceroles and free fatty acids. These results show very low activity of de novo syntheses of lipid from injected glucose in the cod.     

A partial-reuse system for coldwater aquaculture

A model partial-reuse system is described that provides an alternative to salmonid production in serial-reuse raceway systems and has potential application in other fish-culture situations. The partial-reuse system contained three 10 m³ circular ‘Cornell-type’ dual-drain culture tanks. The side-wall discharge from the culture tanks was treated across a microscreen drum filter, then the water was pumped to the head of the system where dissolved carbon dioxide (CO₂) stripping and pure oxygen (O₂) supplementation took place before the water returned to the culture tanks. Dilution with make-up water controlled accumulations of total ammonia nitrogen (TAN). An automatic pH control system that modulated the stripping column fan ‘on’ and ‘off’ was used to limit the fractions of CO₂ and unionized ammonia nitrogen (NH₃---N). The partial-reuse system was evaluated during the culture of eight separate cohorts of advanced fingerlings, i.e., Arctic char, rainbow trout, and an all female brook trout × Arctic char hybrid. The fish performed well, even under intensive conditions, which were indicated by dissolved O₂ consumption across the culture tank that went as high as 13 mg/L and fish-culture densities that were often between 100 and 148 kg/m³. Over all cohorts, feed conversion rates ranged from 1.0 to 1.3, specific growth rates (SGR) ranged from 1.32 to 2.45% body weight per day, and thermal growth coefficients ranged from 0.00132 to 0.00218. The partial-reuse system maintained safe water quality in all cases except for the first cohort—when the stripping column fan failed. The ‘Cornell-type’ dual-drain tank was found to rapidly (within only 1–2 min) and gently concentrate and flush approximately 68–88% (79% overall average) of the TSS produced daily within only 12–18% of the tank’s total water flow. Mean TSS concentrations discharged through the three culture tanks’ bottom-center drains (average of 17.1 mg/L) was 8.7 times greater than the TSS concentration discharged through the three culture tanks’ side-wall drains (average of 2.2 mg/L). Overall, approximately 82% of the TSS produced in the partial-reuse system was captured in an off-line settling tank, which is better TSS removal than others have estimated for serial-reuse systems (approximately 25–50%). For the two cohorts of rainbow trout, the partial-reuse system sustained a production level of 35–45 kg per year of fish for every 1 L/min of make-up water, which is approximately six to seven times greater than the typical 6 kg per year of trout produced for every 1 L/min of water in Idaho serial-reuse raceway systems.     

Purification and partial characterization of Cu, Zn superoxide dismutase from haemolymph of Oriental river prawn Macrobrachium nipponense

The copper plus zinc superoxide dismutase (Cu, Zn-SOD) was purified from haemolymph of the Oriental river prawn, Macrobrachium nipponense and partially characterized. Partial protein precipitation in crude extract was affected by using heat treatment and (NH₄)₂SO₄ fractionated precipitation methods. Fractionation of superoxide dismutase was performed by DEAE-cellulose 32 ion-exchange chromatography and followed by CM-cellulose cation-exchange chromatography. The molecular weight of it was about 66.1 kDa, as judged by SDS polyacrylamide gel electrophoresis. The enzyme was sensitive to cyanide and H₂O₂, and contained 1.08 ± 0.14 atom of copper and 0.98 ± 0.11 zinc per subunit shown in atomic absorption spectroscopy, which revealed that purified SOD was Cu, Zn superoxide dismutase. The purified enzyme had an absorption peak of 269 nm in ultraviolet region and the enzyme remained stable at 25–45 °C within 60 min. But it was rapidly inactivated at higher temperature (50 °C). The activity of purified shrimp Cu, Zn-SOD was remained stable over the range pH 5.8–8.3. Treated with 10 mM mercaptoethanol, the enzyme activity significantly increased. However, the enzyme activity was obviously inhibited by 10 mM CaCl₂, ZnCl₂, SDS, EDTA–Na₂ and 1 mM and 10 mM K₂Cr₂O₇. The results showed that it might be a kind of EC-SOD. And it was the first report of some characterizations of this EC-SOD in M. nipponense.     

Observations on the conditioning of filter bed in hypersaline aquaria

The nitrifying activity of the filter bed of aquaria was monitored in hypersaline conditions. Salinity was raised in 5 ppt steps from normal sea water to 126 ppt in a course of 35 and 41 days. Twenty grey mullet fry (Chelon labrosus and Mugil cephalus) were used in two 53 l aquaria. Daily monitoring of total ammonia–nitrogen (TAN), nitrite, nitrate ions, and pH was performed. After an initial peak of TAN (0.65 mg/l), total ammonia stabilized at safe low levels (0–0.2 mg/l). Nitrite exhibited more peaks at levels of about 10 mg/l, lasted for 3–8 days but they also subsided to almost zero afterwards. Nitrate finally stabilized at levels around 100 mg/l. The water was alkaline, with pH fluctuating in the region of 8.2–8.8. These findings indicate that the filter bed may be effectively conditioned for hypersalinity and that fish may be safely maintained in the aquaria.     

Measurements of oxygen consumption and ammonia excretion of Atlantic salmon (Salmo salar L.) in commercial-scale, single-pass freshwater and seawater landbased culture systems

The oxygen consumption of Atlantic salmon was measured in large culture tanks for a period of 20 months from the parr to the adult stage. In addition, diurnal sampling was conducted for estimation of both oxygen consumption and ammonia excretion. The oxygen consumption was affected especially by temperature, season and smoltification. For parr the oxygen consumption rate was 1–6 mg O₂/kg min and the ammonia excretion rate was 0·037–0·13 mg N/kg min from autumn to spring. The corresponding rates for adult salmon during the period October to July were 1·5–4·5 mg O₂/kg min and 0·075–0·13 mg N/kg min.     

Toxicity of Un-ionized Ammonia and High pH to Post-larval and Juvenile Freshwater Shrimp Macrobrachium rosenbergii

Post-larval and juvenile Macrobrachium rosenbergii were exposed for 72 h at 29 C to four pH levels (8.5, 9.0, 9.5, 10.0) and four concentrations of un-ionized ammonia-nitrogen (0, 1, 2, and 3 mg/L NH_j-N). Results indicated potentiation between NH₃ and high pH. Juveniles were more tolerant of high pH and NH₃ than post-larvae.
For post-larvae, estimates of 72 h LC50 for pH were 9.43, 9.21, and 8.71 at 0, 1, and 2 mg/L NH₃-N, respectively; 72 h LC50 estimates for NH₃-N were 2.18 and 1.45 mg/L at pH levels of 8.5 and 9.0, respectively. For juveniles, estimates of 72 h LC50 for pH were 9.91, 9.56, 9.04, and 8.76 at 0, 1, 2, and 3 mg/L NH₃-N, respectively; 72 h LC50 estimates for NH₃-N were 2.02 and 0.54 mg/L at pH 9.0 and 9.5, respectively.
In pond culture of M. rosenbergii , high pH levels can cause mortality at stocking. The 72 h data can be used as an indication of safe stocking levels of pH and ammonia. These data suggest that post-larvae should not be exposed to pH > 9.0 nor to NH₃-N > 1 mg/L in the pH range 8.5–9.0 and juveniles should not be exposed to pH > 9.5 nor to NH₃-N > 0 mg/L at pH 9.5, > 1 mg/L at pH 9.0, or > 2 mg/L at pH 8.5.     

Effect of Exposure to Potassium Permanganate on Stress Indicators in Channel Catfish Ictalurus punctatus

Juvenile channel catfish Ictulurus punctatus were exposed to 1× (0.44 mg/L), 3× (1.32 mg/L), or 5× (2.19 mg/L) the recommended therapeutic concentrations of waterborne potassium permanganate (KMnO₄) for 36 h to determine the toxicity of the chemical. The fish were observed for 14 d after exposure. Gill, liver, and blood samples were collected before exposure, at 12, 24, and 36 h of exposure, and at 48-h intervals for 14 d thereafter. Analysis of homogenized gill tissue showed a transient increase in manganese content that quickly disappeared once exposure was discontinued. Fish exposed to the 3× and 5× concentrations of KMnO₄ experienced 9 and 50.6% mortality, respectively. Plasma cortisol was elevated more than ten-fold at the 5× concentration. Both plasma chloride and osmolality were significantly reduced at the 3× and 5× concentrations but were unchanged at the 1×. Packed cell volumes (PCV) of whole blood rose significantly in response to 3× and 5× concentrations of KMnO₄ Mortality may have been the result of blood electrolyte depletion as indicated by increased PCVs, loss of chloride, and reduced osmolality. All stress indicators measured, except PCV at the 5× concentration, were indistinguishable from unexposed controls within 48 h after exposure was discontinued. At the l× concentration (the concentration most like that employed in a disease treatment) no changes were observed in any stress indicators measured suggesting that KMnO₄ may be safely used as a disease therapeutant for channel catfish.     

Performance and operation of a rotating biological contactor in a tilapia recirculating aquaculture system

This paper describes the performance characteristics of an industrial-scale air-driven rotating biological contactor (RBC) installed in a recirculating aquaculture system (RAS) rearing tilapia at 28 °C. This three-staged RBC system was configured with stages 1 and 2 possessing approximately the same total surface area and stage 3 having approximately 25% smaller. The total surface area provided by the RBC equaled 13,380 m². Ammonia removal efficiency averaged 31.5% per pass for all systems examined, which equated to an average (± standard deviation) total ammonia nitrogen (TAN) areal removal rate of 0.43 ± 0.16 g/m²/day. First-order ammonia removal rate (K₁) constants for stages 1–3 were 2.4, 1.5, and 3.0 h⁻¹, respectively. The nitrite first-order rate constants (K₂) were higher, averaging 16.2 h⁻¹ for stage 1, 7.7 h⁻¹ for stage 2, and 9.0 h⁻¹ stage 3. Dissolved organic carbon (DOC) levels decreased an averaged 6.6% per pass across the RBC. Concurrently, increasing influent DOC concentrations decreased ammonia removal efficiency. With respect to dissolved gas conditioning, the RBC system reduced carbon dioxide concentrations approximately 39% as the water flowed through the vessel. The cumulative feed burden – describes the mass of food delivered to the system per unit volume of freshwater added to the system daily – ranged between 5.5 and 7.3 kg feed/m³ of freshwater; however, there was no detectable relationship between the feed loading rate and ammonia oxidation performance.     

Early biochemical biomarkers for zinc in silver catfish (<Emphasis Type="Italic">Rhamdia quelen</Emphasis>) after acute exposure

Contamination of aquatic ecosystems by metals causes various biochemical changes in aquatic organisms, and fish are recognized as indicators of environmental quality. Silver catfish were exposed to six concentrations of zinc (Zn): 1.0, 2.5, 5.0, 7.5, 10.0 and 12.5 mg/L for 96 h to determine the mean lethal concentration (LC₅₀). The value obtained was 8.07 mg/L. In a second experiment, fish were exposed to concentrations of 1.0 or 5.0 mg/L Zn and a control for 96 h. Afterward, the tissues were collected for biochemical analysis. Lipid peroxidation, as indicated by thiobarbituric acid-reactive substance (TBARS), decreased in the liver and brain for all Zn concentrations tested, while in the gills TBARS levels increased at 1.0 mg/L and declined at 5.0 mg/L. Zn increased protein carbonyls in the muscle of silver catfish and decreased it in the other tissues. The enzyme superoxide dismutase increased in both exposed groups. However, catalase did not change. Glutathione S-transferase decreased in the liver and increased in the gills (1.0 mg/L), muscle (5.0 mg/L) and brain (1.0 and 5.0 mg/L). Nonprotein thiols changed only in brain and muscle tissue. Zn exposure inhibited acetylcholinesterase (AChE) activity in the brain at both concentrations tested, but did not change it in muscle. Exposure to Zn inhibited the activity of Na⁺/K⁺-ATPase in the gills and intestine at both concentrations tested. Our results demonstrate that Zn alters biochemical parameters in silver catfish and that some parameters such as AChE and Na⁺/K⁺-ATPase could be considered as early biomarkers of waterborne Zn toxicity.