The effects of elevated pCO2 on growth,shell production and metabolism of cultured juvenile abalone,Haliotis iris

Reduced seawater pH and elevated pCO₂ are important considerations in tank‐based abalone aquaculture, while sea‐based farms may be at risk to ocean acidification reductions in pH. Juvenile Haliotis iris (5–13 and 30–40 mm shell length) were reared in two, 100‐day experiments at ambient pH_nbs (~ 8.1, 450 μatm CO₂), pH 7.8 (~1000 μatm CO₂) and pH 7.6 (~1600 μatm CO₂). Seawater pH was measured and adjusted automatically by bubbling CO₂ into water in replicated flow through tanks. Two separate trials were run, in winter (8.8°C) and summer (16.5°C). Survival and growth were monitored every 30 days, and post experiment measurements of morphometrics and respiration rate undertaken. Growth of shell length and wet weight were negatively affected by reduced pH, with a 2 to 3‐fold reduction in growth of both size classes between ambient and pH 7.6 treatments in the summer experiment. For small juveniles, growth reductions were in conjunction with decreases to shell weight, while large juveniles showed greater resilience in shell production. No changes to respiration rate occurred, suggesting that juveniles may maintain physiological functioning while tolerating dissolution pressure or that they are unable to upregulate metabolism to compensate for pH effects. These data show that CO₂ driven reductions in pH can impact growth, metabolism and biomineralization of abalone, and indicate that water quality and ocean acidification are of importance in aquaculture of the species.     

The effects of elevated concentrations of dissolved inorganic phosphate in seawater on the growth and survival of juvenile abalone,Haliotis iris

Seawater sampling from three abalone farms in New Zealand showed average ambient concentrations of dissolved inorganic phosphate (P_i) varying between 2.36 and 238 μM. The P_i concentration within each system appeared to be directly linked to the percentage of water that was replaced each day. An experiment was conducted over 5 months to examine the effect of elevated P_i concentrations on the growth of two juvenile abalone (Haliotis iris) size classes (small: average shell length=23.9 ± 0.1 and large: average shell length=61.9 ± 0.1 mm). Abalone from each size class were exposed to P_i concentrations of; (a) natural incoming seawater (average 0.12 ± 0.12 μM), (b) 10.7 ± 1.3 μM, (c) 60.9 ± 5.8 μM and (d) 113.1 ± 5.6 μM. The results suggest that over the course of the 5‐month period of this experiment there was a significant negative impact on growth (shell length and wet weight) when the smaller size class of abalone were exposed to P_i concentrations greater than 10.7 μM and for the large size class of abalone when exposed to greater than 60.9 μM P_i. However, elevated P_i concentrations did not significantly impact on abalone survival during the course of the experiment.     

Ammonia toxicity and its effect on the growth of the South African abalone Haliotis midae Linnaeus

The current study investigated acute toxicity to ammonia of the South African abalone, Haliotis midae, from three size classes relevant to mariculture operations, and the chronic impact of sub-lethal ammonia levels on growth of juvenile abalone.Results showed that tolerance to ammonia (at pH 7.8 and T_a = 15 °C) increases with body size (i.e. age) as indicated by 36 h LC₅₀ values: juvenile abalone (1-2.5 cm shell length) had the lowest LC₅₀ of 9.8 μg l^− 1 FAN, whereas LC₅₀ was 12.9 μg l^− 1 FAN in “cocktail”-size abalone (5-8 cm shell length). The highest LC₅₀ of 16.4 μg l^− 1 FAN was observed in “brood stock”-size animals (10-15 cm). When “cocktail”-size abalone were allowed to acclimatize to sub-lethal ammonia levels for 48 h, their ammonia tolerance increased compared with non-acclimatized abalone of the same size: LC₅₀ was 2.0 μg l^− 1 FAN higher at 14.8 μg l^− 1 FAN.Growth of juvenile abalone (1-2.5 cm shell length) during chronic exposure to sub-lethal FAN levels is inhibited: specific growth rate (SGR) is significantly reduced by 58.7% to 0.10 ± 0.03% d^− 1 (weight) compared with 0.24 ± 0.06% d^− 1 of abalone of a control group (no ammonia).The results demonstrate the negative effects of ammonia not only on survival but also on growth of farmed abalone, both impair profitability of the farming operation. The information from the present study will be helpful in determining water quality requirements in South African abalone farms.     

Protective effects of dietary selenium on abalone Haliotis discus hannai against the toxicity of waterborne cadmium

This study was conducted to investigate protective effects of dietary selenium (Se) on abalone Haliotis discus hannai Ino against the toxicity of cadmium (Cd). A 60‐day feeding trial was conducted with abalone (initial weight: 3.17 ± 0.01 g), which were exposed to 0.34 mg/L of waterborne Cd. During a feeding trial, abalone were fed graded levels of Se at 0.10 (controls), 1.31, and 4.20 mg/kg diet respectively. Results showed that there was no significant difference in specific growth rate and survival rate of abalone among the three treatments. Compared with the controls, dietary Se significantly decreased Cd concentrations in serum, muscle, mantle, gill, mantle, and hepatopancreas of abalone. Besides, compared with the controls, dietary Se significantly increased metallothionein concentration in the hepatopancreas of abalone. Additionally, compared with the controls, dietary Se significantly decreased concentrations of malondiadehyde and protein carbonyl in hepatopancreas of abalone. Meanwhile, compared with the controls, dietary Se significantly increased activities of glutathione peroxidase, thioredoxin reductase, and thioredoxin peroxidase, and concentration of glutathione in the hepatopancreas of abalone. Based on the data above, in abalone, dietary Se showed protective effects against waterborne Cd.     

Accumulation of Heavy Metals in the Nauplii of Artemia salina

Artemia salina cysts (San Francisco Bay Brand) were exposed in seawater containing multiple concentrations of either a single heavy metal (Hg, Cu, Zn, Pb, Cd, Co, Ni, Cr, Mn and Fe) or combination of heavy metals. The heavy metal accumulation in Artemia nauplii increased linearly with an increase in the heavy metal concentration in water. The metals could be detected in nauplii exposed to a single heavy metal at dosages of 5 μg/L for Hg, Zn, Mn, Fe and Cu; 25 μg/L for Cd and Cr; 50 μg/L for Co; 100 mUg/L for Ni; and 250 μg/L for Pb. Cysts exposed to several heavy metal combinations had minimum effective dosages equal to or lower than the single heavy metals- 5 μg/L for Cu, Cr, Zn, Mn and Fe; 25 μg/L for Cd and Ni; 50 μg/L for Co; and 250 μg/L for Pb. The accumulation of Cu, Ni and Co by Artemiu nauplii did not differ for animals exposed to single or combined heavy metal solutions. Cr, Zn and Pb had a synergistic effect of heavy metal uptake in combined heavy metal element solutions, however, Fe, Cd and Mn had an antagonistic effect.     

Reconstitution of muscle F‐actin from Atlantic salmon (Salmo salar L.) with carotenoids—binding characteristics of astaxanthin and canthaxanthin

The binding of carotenoids to the myofibrillar protein F‐actin purified from the white muscle of Atlantic salmon (Salmo salar L.) was studied using in vitro reconstitution. The binding of astaxanthin and canthaxanthin was saturable, and analysis revealed the presence of a single carotenoid‐binding site. The dissociation constants (K_d) for actin prepared from 2.5 kg FW (Fresh Weight) fish were 1.04 ± 0.13 μg carotenoid per milligram of actin and 0.54 ± 0.11 μg/mg for astaxanthin and canthaxanthin, respectively. The saturation binding level (B_max) for astaxanthin was 1.39 ± 0.07 μg/mg and 1.04 ± 0.08 μg/mg for canthaxanthin. These values were higher for F‐actin prepared from organic and small (~0.5 kg FW) salmon than for non‐organic and larger, mature fish. The structural specificity of carotenoid binding revealed a preference for carotenoids that possess a keto group at C‐4 on the β end group of the molecule, but the presence of hydroxyl groups at C‐3 or C‐4 reduced overall binding efficiency. The study suggests that the ability of myofibrillar proteins to bind carotenoids is not a limiting factor governing the deposition of carotenoids in the muscle of salmonids.     

Influences of dietary antimicrobial peptide APSH‐07 on the growth performance,immune response and vibriosis resistance of abalone Haliotis discus hannai Ino

A 115‐day feeding trial and subsequently a 10‐day challenge test with Vibrio parahaemolyticus were conducted to investigate the effects of dietary antimicrobial peptide APSH‐07 on growth performance, immune response, antioxidative status and vibriosis resistance of abalone Haliotis discus hannai (initial body weight: 2.06 ± 0.01 g; initial shell length: 25.42 ± 0.18 mm). Four artificial diets were designed with 0 (artificial diet control), 7.5, 15.0 and 22.5 mg/kg of APSH‐07, respectively. The brown alga Laminaria japonica was used as the live food control. Results showed that the specific growth rates of abalone in the groups with 7.5 and 15.0 mg/kg dietary APSH‐07 were significantly higher than those in the controls (p < .05). The total haemocyte counts and respiratory burst activity in haemolymph of abalone in the group with 7.5 mg/kg of dietary APSH‐07 were significantly higher than those in the groups with 0 and 22.5 mg/kg of dietary APSH‐07 (p < .05). The gene expression levels of Mn‐superoxide dismutase and thioredoxin peroxidase 2, and the activities of glutathione peroxidase in the group with 7.5 mg/kg of dietary APSH‐07 were significantly higher than those in the other groups (p < .05). Cumulative mortality of abalone after the challenge test was significantly decreased in the group with 7.5 mg/kg of dietary APSH‐07 supplementation. Supplementation of 22.5 mg/kg dietary APSH‐07 significantly increased the cumulative mortality. In conclusion, 7.5 mg/kg of dietary APSH‐07 supplementation had the better growth performance, higher antioxidation, immune and disease resistance capacity of abalone. Excessive supplementation of dietary antimicrobial peptide APSH‐07 (22.5 mg/kg) had significantly negative effects. Further studies are needed to determine the optimal level of dietary APSH‐07 supplementation for abalone.     

Effect of Hybrid Abalone,Haliotis discus hannai × Haliotis discus discus,Cultivation on the Carbon Cycle: Carbon Source/Sink

Respiration, calcification, and bio‐deposition of hybrid abalone, Haliotis discus hannai × Haliotis discus discus, fed on different foodstuffs have been measured to evaluate the effect of hybrid abalone culture on carbon source/sink in coastal areas. Fed with Laminaria japonica, Undaria pinnatifida, Gracilaria lemaneiformis, U. pinnatifida, and Ulva pertusa, alternated mutually, the carbon bio‐deposition rate of hybrid abalone was 24.29 ± 6.39, 65.40 ± 10.55, 21.48 ± 5.99, and 29.28 ± 6.47 µg/g/h, respectively. Hybrid abalone fed on U. pinnatifida had a higher carbon bio‐deposition rate compared to that fed on other foodstuff (P < 5%). Rate of CO₂ released by respiration of hybrid abalone fed on the experimental foodstuff was 24.53 ± 8.57, 32.73 ± 7.99, 29.31 ± 6.39, and 33.67 ± 12.37 µg/g/h, respectively. Results indicated that calcification presented less relationship with body weight type of the foodstuff. The rate of CO₂ released by calcification into seawater and atmosphere was 2.77 ± 1.89 and 6.53 ± 3.36 µg/g/h, respectively. The total rate of CO₂ released because of bio‐deposition, respiration, and calcification processes was 16.19 ± 4.67 µg/g/h, while the total rate of carbon sequestered in shells and tissues was 8.94 ± 2.07 µg/g/h. The study revealed that hybrid abalone culture is a source of CO₂.     

Heavy metal residues in dulse,an edible seaweed

Dulse from three geographically different areas and a common holding tank was analyzed for As, Cu, Cd, Pb, Se, Zn and Hg by flameless atomic absorption spectroscopy. Concentration ranges (μg/g dry weight) were: As 5.50-7.50, Cu 3.90-6.34, Cd 0.97-2.65, Pb 0.688-3.5, Se 2.00–2.91, Zn 57.5–84.1, Hg < 0.02. Percent moisture was 13.50-23.45.     

Shrimp shell as a potential sorbent for removal of arsenic from aqueous solution

This study examined the ability of shrimp shell to remove arsenic (As) from aqueous solutions. The shells of two species of shrimp, black tiger shrimp Penaeus monodon and white shrimp Litopenaeus vannamei, were chosen to be the sorbents. Laboratory exposure experiments estimated uptake and depuration rate constants (i.e., k ₁ and k ₂) as well as the bioconcentration factors (BCF) of the shells of the two shrimps. A first-order one-compartment model was presented to describe the uptake kinetics of As in shrimp shell. The resulting k ₁, k ₂, and BCF values of black tiger shrimp were 0.034–1.722 ml/g/day, 0.007–0.345 g/g/day, and 5.08 ± 1.56 ml/g, while those for white shrimp were 0.053–0.523 ml/g/day, 0.011–0.237 g/g/day, and 3.95 ± 1.88 ml/g, respectively. The sorption capacities of black tiger shrimp shell and white shrimp shell were 1.08 × 10⁻⁴–6.66 × 10⁻³ and 1.04 × 10⁻⁴–3.26 × 10⁻³ mmol/g, respectively. The sorption capacity of shrimp shell increased with the initial As concentration in water. Shrimp shell, as a waste material, could be potentially used for the removal of As from an aqueous medium. Although the As-removal capacity of shrimp shell was lower than those of natural and chemical sorbents, using shrimp shells as sorbents is less expensive and could increase the additional value of shrimp products.     

Octopus as predators of abalone on a sea ranch

This study examined the occurrence of octopus across an abalone, Haliotis laevigata, Donovan, sea ranch in south‐western Australia, to understand how octopus may be impacting abalone production. Commercial divers removed 654 octopus and 17,666 empty abalone shells during regular, 2 to 4‐weekly surveys over 27 months. A negative binomial generalised linear model estimated a 78% increase in empty shells per artificial abalone habitat per day, when octopuses were present, after adjusting for location and season. Of the 408 shells examined for evidence of predation, 19% had a small, slightly ovoid hole consistent with those made by octopus. The mean (± 1 SE) length of shells with boreholes (70.3 ± 2.2 mm) was significantly longer than those without (59.8 ± 0.5 mm), and boreholes were concentrated over the adductor, respiratory organs and heart. This study provides important insights into the adaptable feeding regimes of octopus and their potential to impose strong top‐down controls on sea ranching operations.     

Effect of dietary microminerals in early weaning diets on growth,survival, mineral contents and gene expression in gilthead sea bream (Sparus aurata,L) larvae

In previous studies, combined inclusion of Zn, Mn and Se in early weaning diets improved larval growth, but suggested a potential toxicity by one of these elements. The present study aimed to determine the effect of the single inclusion of Zn, Mn, Se or Cu, their combination (Control+) or their absence (Control?) on larval diets. At the end of the trial, survival was significantly (p < .05) lowest in fish fed C+ diet (17.16 ± 7% mean ± SD), followed by that of larvae fed Mn diet (21.91 ± 7%). The highest survival was obtained by Cu diet (35.27 ± 15%), followed by C? diet (34.58 ± 9%). Cu and Se supplementation significantly improved total length and body weight, in comparison with the C? fish. On the contrary, fish fed Mn and C+ showed the lowest growth. Supplementation with Zn or Cu significantly increased CuZnsod, whereas gpx was significantly upregulated in fish fed Se and C+ diets. ARA/EPA level was significantly highest and DHA/EPA lowest in larvae fed the Cu diet in fish fed C+ diet. The results pointed out the importance of supplementation with Cu, as well as Se and Zn, on early weaning diets for gilthead sea bream, and the potential toxic effect of Mn.     

四种重金属暴露对青鳉呼吸行为的毒性效应

研究青鳉对不同重金属污染物的敏感性和响应阈值,为水体污染特别是重金属污染的早期预警监测提供定量基础。青鳉3月龄,体长(1.5±0.1) cm,体重(0.15±0.01) g;4种重金属为Cd、Zn、Cu和Hg。研究结果表明:青鳉对Cu~(2+)、Zn~(2+)、Cd~(2+)和Hg~(2+)的急性致死毒性大小为Hg~(2+)Cu~(2+)Cd~(2+)Zn~(2+);Hg~(2+)、Cu~(2+)和Cd~(2+)暴露下青鳉呼吸频率和呼吸强度先升高再降低(P0.01),呼吸参数与重金属浓度间呈现倒"U"型关系;Zn~(2+)暴露下青鳉呼吸频率、呼吸强度显著下降(P0.01);青鳉呼吸行为对Cu~(2+)、Zn~(2+)、Cd~(2+)和Hg~(2+)4种重金属暴露的响应阈值和响应时间分别为0.15、0.95、0.15、0.045 mg/L和2 h 32 min、4 h 7.5 min、3 h 5.5 min、4 h 37 min,响应阈值与96 h LC_(50)的比值分别为0.43、0.19、0.33、0.77。青鳉对Cd~(2+)、Zn~(2+)、Cu~(2+)、Hg~(2+)污染较为敏感,其呼吸参数可作为突发性水体重金属污染的生物监测指标。     

The Larval Development,Metamorphosis and Juvenile Growth of the Turban Snail Lithopoma (Astraea) undosa (Wood, 1828) (Gastropoda:Turbinidae)

This work presents the embryonic, larval, and postlarval development of Lithopoma undosa (L. undosa) (20 ± 2 C and the effect of natural inducers on the larval metamorphosis. Embryonic development until hatching of the trochophore larva took 15 h. Early veliger larvae with well‐developed shell were after 24 h. At 48 h, the operculum was completely formed. Cephalic tentacles were visible after 72 h. Larvae reached competence 6 to 7 d after fertilization, and was characterized by the presence of branched cephalic tentacles. The effect of natural inducers was evaluated. The percentage of metamorphosis with diatoms and adult mucus was 94% and 58% respectively, differing from the 25% without inducer. When was repeated, the metamorphosis was 100%, and 16% with benthic diatoms. The initial mean size of the postlarvae was 0.316 ± 0.02 mm. After 264 d the juveniles had attained a mean size of 5.98 ± 0.16 mm. These results will not only be of use in the evaluation of the culture of L. undosa, but also in studies on the characterization of inducers.     

Growth performance and feed utilization of Haliotis tuberculata coccinea (Reeve) juveniles from the Azores (north-eastern Atlantic Ocean): An assay of three mono algae diets

We assessed the dietary value of available seaweeds (Ulva lactuca, Ulva intestinalis, and Sargassum vulgare) as food for juvenile abalone Haliotis tuberculata coccinea. During the 6 weeks that the experiment lasted, initial shell length and weight increased from 13.95 ± 0.32 mm to 15.30 ± 0.30 mm and from 0.39 ± 0.02 g to 0.47 ± 0.03 g. Ulva lactuca diet resulted in higher shell growth rate (58.47 ± 16.76 μm day^?1), SGR (1.15 ± 0.47%.day^?1), weight gain (65.5% ± 33.3), and PER (1.56 ± 0.31), possibly thanks to its higher crude protein content. Both green algae (U. lactuca, U. intestinalis) prove to support the growth of H. tuberculata coccinea. However, they might not be appropriate for an optimal intensive aquaculture production; further research should be conducted to find more efficient diets for juvenile abalone.     

Assessment of Levels and Potential Health Risk of Heavy Metals in Water and Selected Fish Species from the Benue-Niger River Confluence,Lokoja, Nigeria

The concentrations of cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu), zinc (Zn), and iron (Fe) in water and selected fish species (Oreochromis nilzinc (oticus and Clarias gariepinus) from Benue-Niger River Confluence, Nigeria were investigated. The water and fish sample digests were quantified using an atomic absorption spectrophotometer. The study aimed to assess any possible human health risk associated with water and fish consumption from the selected geographical area. The concentration of the metals in the surface water ranged from 0.007 to 0.039, 0.106 to 0.240, 0.092 to 0.0164, 0.682 to 0.878, 0.058 to 0.309, and 0.136 to 1.645 mg/L for Cd, Cr, Cu, Fe, Pb, and Zn, respectively, while the concentrations of the metals, Cd, Pb, Cr, Cu, Zn, and Fe in these fish species ranged from 0.034 to 0.679, 0.500 to 1.75, 0.152 to 0.351, 0.36 to 1.01, 5.32 to 7.41, and 4.25 to 9.17 mg/kg, respectively. Cd, Cr, and Pb levels in fish were higher than the provisional tolerable weekly intake of 7, 1.5, and 25 μg/kg bw, respectively, according to the World Health Organization. Dry season values of the metals in water samples were higher, and sharptooth catfish had higher amounts of the metals. The hazard quotient (HQ) for Cd indicated a possible potential health concern with fish consumption from this area.     

Optimization of growth requirements and scale‐up cultivation of freshwater algae Desmodesmus armatus using response surface methodology

In order to optimize the optimal cultivation conditions of freshwater algae Desmodesmus armatus for biomass production. In this study, the optimum source of carbon, nitrogen and intensity of light were investigated. Particularly, the variables which are affect the biomass of D. armatus was screened by the Plackett‐Burman (PB) method. Furthermore, the optimized medium composition using central composite design (CCD) of response surface method (RSM) central for D. armatus was reconstituted accordingly to have 0.93 g/L nitrate, 0.04 g/L phosphate, 0.15 g/L magnesium sulphate and 0.07 g/L bicarbonate, and optimum growth conditions of temperature at 27°C, light intensity of 108 μmol m^?2 s^?1, pH 7.00 and air flow of 0.50 L/min. After 12 days, the biomass, protein and polysaccharose content were 1.65 ± 0.15 g/L, 53.61 ± 1.25% and 6.15 ± 0.43%, respectively. Finally, the optimized conditions were applied to the outdoor 800‐L photobioreactor for scale‐up cultivation.     

Effect of increased irradiance and thermal stress on the symbiosis of Symbiodinium microadriaticum and Tridacna gigas

The impetus for this study was the mass bleaching event of giant clams in 1997–1998 at several reefs in the Great Barrier Reef (GBR, Australia). From September until December 1999, the study investigated the effects of high light intensities and increased temperature accompanied by a nutrient limitation on the metabolism of Tridacna gigas, to test, if these environmental changes can induce bleaching. In a 50-day trial similar conditions of the mass bleaching event were imitated stressing clams, collected from Orpheus Island and Nelly Bay, by a two- to threefold light intensity and an increased temperature of 4–6 °C. The objectives of the experiments were to determine whether high light intensities can induce changes in chlorophyll content or alter zooxanthella cell sizes and populations in the tissue. After 50 days of exposure to high light intensity the mantle tissue of stressed clams exhibited a decreased number of zooxanthellae per unit area from 19.8 ± 0.8 (× 10⁷·cm^–2) to 0.2 ± 0.2 (× 10⁷·cm^–2) (mean ± CL). Additionally, the average cell size of zooxanthellae were downsized from 7.4 ± 0.1 μm to 5.3 ± 0.1 μm (mean ± CL). Subsequently, the chlorophyll content of both, chl a and chl c₁, declined as well, chl a from 192 ± 4 to 0.1 ± 0.1 μg·ml^–1 and chl c₁ from 145 ± 6 to 0 μg·ml^–1 (mean ± CL). This study shows that increased light intensity and temperature are the main causes for bleaching in giant clams. Thus, the study confirmed the four major aspects involved in bleaching: (1) loss of symbiotic algae, (2) decrease of chl a/c₁ in the remaining symbiotic algae, (3) retention of small zooxanthellae in the tissue and (4) release of ammonium (NH₄⁺) into the water column while nutrient uptake of ammonium was largely blocked.     

Effects of flow velocity on growth,metabolism and nitrogen and phosphorus budget of Haliotis discus hannai Ino in a recirculating aquaculture system

To study the effects of different flow velocities on growth, metabolism and nitrogen (N) and phosphorus (P) budget of Haliotis discus hannai Ino in a recirculating aquaculture system, abalones (shell length: 45.71 ± 3.09 mm, body weight: 8.62 ± 0.75 g) were cultured at three different flow velocities with four replicates each: high (400 L/hr), medium (300 L/hr) and low (200 L/hr). At the end of the 70 days experiment, the survival rate, food intake and P utilization rate of abalones in the 200 L/hr group were significantly lower than those in any other group (p < .05), whereas the total ammonia nitrogen and nitrite nitrogen concentrations in the water were significantly higher than those in any other group (p < .05). The body weight specific growth rate, food conversion efficiency, abalone‐harvested N and P outputs and N utilization rate were ranked as follows: 300 > 400 > 200 L/hr (p < .05). In the 300 L/hr group, the activities of hexokinase, pyruvate kinase and lactate dehydrogenase were significantly lower than those in the 400 L/hr group, whereas the activity of succinate dehydrogenase was significantly higher than that in the other two groups (p < .05). Aerobic metabolism was the main source of energy acquisition for abalones in the 300 L/hr group. In the 400 L/hr group, the expression levels of manganese superoxide dismutase and thioredoxin peroxidase significantly increased from Day 35 to Day 70, but they still were significantly lower than the values in the 200 L/hr group (p < .05). In the 200 L/hr group, the expression levels of catalase and heat shock protein 70 were significantly higher than those in any other group, and they significantly increased from Day 35 to Day 70 (p < .05). These results indicate that maintaining flow velocity at 300 L/hr will minimize oxidative damage due to deterioration of water quality, reduce the energy consumption required for organisms to resist the impact of water flow, improve the N and P utilization rates of the recirculating aquaculture system, and reduce the cost of culturing abalones.     

Growth,water quality and oxidative stress of Nile tilapia Oreochromis niloticus (L.) in biofloc technology system at different pH

The objective of this study was to demonstrate the pH effects on growth, survival, water quality, proximal composition of bioflocs and oxidative stress of Nile tilapia in biofloc technology (BFT) system. Twenty‐five fish (3.68 ± 0.93 g) were distributed in each tank (useful vol. 37.5 L), utilizing treatments with pH 8.3, 7.5 and 6.5 at 60 days. During the experiment, the oxidation of total ammonia was similar among the treatments. However, the NO₂^?‐ N oxidation was slower at pH 6.5 (10.1 ± 1.0 mg/L) compared to pH 7.5 (7.0 ± 0.6 mg/L) and 8.3 (7.1 ± 1.5 mg/L). The final weight was higher for pH 7.5 treatment (44.1 ± 0.9 g) compared to pH 8.3 (37.1 ± 3.9 g), while the pH 6.5 (40.4 ± 4.1 g) was like to the other treatments. Moreover, the survival, daily growth rate and the food conversion rate were not affected by treatments. When evaluating physiological and biochemical parameters, no alterations were detected, therefore, indicating that fish have a good health status. Thus, the present study demonstrates that BFT for a Nile tilapia nursery, utilizing pH 6.5–7.5, promotes the best results in terms of growth, net yield and efficiency.