High Stocking Density (high + stocking_density)

Distribution by Scientific Domains

Selected Abstracts

Ammonia-, Sodium Chloride-, and Calcium Sulfate-induced Changes in the Stress Responses of Jundiá, Rhamdia quelen, Juveniles

Paulo César Falanghe Carneiro
Salt (NaCl) and gypsum (CaSO4) are used as water additives to mitigate fish stress and improve specimen survival. High stocking densities and the transportation of fish can increase aqueous ammonia, which can, in turn, alter fish cortisol secretion. The objectives of this study were to assess the effects of salt, gypsum, and aqueous ammonia on some stress-induced physiological responses of jundiá, Rhamdia quelen, juveniles induced by captivity and handling, and to determine the lethal ammonia concentration for this species. Jundiá juveniles were subjected to the following five treatments: water only, water + ammonia (0.4 mg/L), water + NH3 + NaCl (6 g/L), water + NH3 + gypsum (150 mg/L), and water + NH3 + NaCl + gypsum. Blood samples were taken after intervals of 1, 5, 24, and 96 h, and the concentrations of cortisol, glucose, chloride, ammonia, and hematocrit were determined. The NH3 LC50 value after 96 h of exposure (LC50,96h) was measured to be 1.9 mg/L NH3. Either salt or gypsum reduced both cortisol and glucose levels during most of the experimental period, but the combination of both reduced these levels even further. The combined use of NaCl and CaSO4 demonstrates a synergic effect on mitigating stress responses induced by handling and aqueous ammonia in jundiá juveniles. [source]

Coping strategies in farmed African catfish Clarias gariepinus.

Does it affect their welfare?
The objective of this study was to assess whether and how coping strategies affect the welfare of African catfish Clarias gariepinus housed at low and high densities. Group composition influenced feed intake; re-active groups (comprised of 100% re-active fish) had a lower specific growth rate (G) and feed intake and a higher feed conversion ratio (RFC) than pro-active groups. Furthermore, re-active groups had a lower energy retention than pro-active groups. The latter was fully due to differences in feed intake, since energy partitioning (on % total gross energy intake basis) was similar among the group composition treatments. Fish held at high stocking density showed a higher RFC and feeding speed and a lower energy retention and agonistic behaviour. None of the measured variables was influenced by the interaction effect. In mixed groups, G and number of skin lesions seemed to be affected by different behavioural phenotypes at low stocking density, but not at high density. These results indicate that both stocking density and group composition affect physical and behavioural responses of C. gariepinus. Furthermore, physical and behavioural data of individual fish housed in mixed groups suggest that coping strategy affects the fitness of different behavioural phenotypes at low, but not at high, stocking density. [source]

Responses to handling and confinement stressors in juvenile great sturgeon Huso huso

B. Falahatkar
The effects of acute stressors on physiological responses of juvenile great sturgeon or beluga Huso huso L. were investigated in two experiments. In the first experiment, fish were handled by placing them in containers at either low density (LD, one fish l,1) or high density (HD, four fish l,1) for 60 s. Concentrations of plasma cortisol, glucose and lactate were determined from blood collected at 0, 1, 3, 6 and 12 h after application of the stressor. Plasma cortisol concentrations increased after the disturbance in H. huso from both handling treatments, but changes were not significant. Plasma glucose rose significantly by 22·9 and 31·6% in LD and HD handling treatments, respectively, after 3 h. Significant increases in plasma lactate occurred within 1 h in both treatment groups, but that of the HD group was much higher. In the second experiment, fish were held at two different densities, LD (2 kg m,2 tank bottom surface area) and HD (7 kg m,2), for 8 weeks and then subjected to an aerial emersion handling stressor in a net for 60 s; blood samples were taken before handling (resting, 0 h) and at 1, 3, 6 and 9 h after handling. Plasma cortisol increased significantly in fish from the HD treatment from 8·8 ± 0·3 to 19·2 ± 2·4 ng ml,1 (mean ±s.e.) by 1 h after stress, but post-handling changes in the LD group were not significant. Significant increases in both plasma glucose and lactate were observed by 1 h in both treatment groups, with peak levels of plasma glucose evident at 3 h [69·4 ± 2·9 and 60·9 ± 1·7 mg dl,1 (mean ±s.e.) in LD and HD groups, respectively]. Plasma glucose levels were significantly higher in the LD group than in the HD group at 3 and 6 h. Post-handling haemoglobin content increased by 1 h and white blood cell numbers were reduced by 3 and 6 h in the HD treatment group compared with resting values, but changes in these blood features in the LD group were not significant. Acute handling did not affect haematocrit in either treatment. The results suggest that H. huso is relatively resistant to handling and confinement, and could tolerate normal hatchery practices associated with aquaculture. Because changes in cortisol concentrations were relatively low compared with those in most teleosts, glucose and lactate concentrations may be more useful as stress indicators in juvenile H. huso. This study also demonstrated that prior exposure to a chronic stressor, specifically high stocking density, could alter the physiological response to subsequent acute handling in H. huso. [source]

Effects of Artificial Substrate and Stocking Density on the Nursery Production of Pacific White Shrimp Litopenaeus vannamei

Komarey R. K. Moss
Nursery production may be enhanced by the addition of artificial substrate to increase the surface area upon which shrimp graze and to serve as refuge. The objective of this study was to assess the effects of the artificial substrate, AquaMatsTM, on the performance of postlarval Pacific white shrimp Litopenaeus vannamei stocked at three densities. Eighteen 230-L tanks were stocked with 10-d postlarvae (mean weight < 0.01 g). Six treatments were evaluated and consisted of shrimp stocked at three densities (778 shrimp/m2, 1,167 shrimp/ m2, and 1,556 shrimp/m2) with and without access to artificial substrate. Shrimp in all treatments received a commercial diet ad libitum. After 6 wk, shrimp were harvested from each nursery tank, counted, and batch weighed. Mean final weight, survival, production, feed conversion ratio, and water quality parameters were analyzed by 2-way ANOVA. There were highly significant (P < 0.001) density and substrate effects on final weight, but there was no significant interaction effect. Final weight was 26.0, 17.4, and 34.5% greater in treatments with substrate than without substrate when stocked at 778, 1,167, and 1,556 shrimp/m2, respectively. There was no significant density, substrate, or interaction effect on survival or water quality. Mean survival was ± 89.1% for all treatments. Increased shrimp growth in the presence of added substrate was likely due to the availability of attached particulate organic matter on the AquaMatsTM that served as an additional food source. Results from this study indicate that artificial substrate can be used to mitigate the potential negative effects of high stocking density on growth of L. vannamei in nursery systems. [source]

Effects of water flow rate on growth rate, mortality and biomass return of abalone in slab tanks

Matthew Wassnig
Abstract The capital-intensive nature of land-based abalone farming demands that infrastructure be fully utilized. This study investigated whether the negative impact of high stocking density in shallow raceway tanks could be ameliorated by optimizing water flow. We quantified the effect of flow rate (87,246 L min,1) on the performance of 2-year-old hybrid abalone (Haliotis laevigata and Haliotis rubra) held at two stocking densities (11400 and 7600 tank,1). A 50% higher density yielded a 27% increase in biomass gain, despite a 10% growth reduction and 3% higher mortality. At the lower density, there was an optimal flow rate of approximately 200 L,1, at which biomass gain was 474 kg and the feed conversion ratio (FCR) was 1.31. At the higher density, biomass gain (max = 658 kg) and FCR (min = 1.41) improved linearly with increasing flow, suggesting that an optimal flow rate exists at 246 L,1 or beyond those tested. Increased oxygen availability with increasing flow is thought to have enhanced abalone performance, although flows greater than 200 L min,1 may have reduced performance at low density due to feed washout and nutrient leaching. Overall, greater financial return per tank was favoured by the combination of high stocking density and high water flow. [source]

Physiological responses of juvenile wedge sole Dicologoglossa cuneata (Moreau) to high stocking density

Marcelino Herrera
Abstract Physiological responses to a high stocking density were tested in juvenile wedge sole Dicologoglossa cuneata (Moreau). Fish were kept at low (1 kg m,2), medium (3 kg m,2) and high (9 kg m,2) stocking densities for 22 days. No differences in the weight, length, survival and hepatosomatic index were observed among treatments. Basal plasma cortisol and osmolality were found to be directly and positively related to stocking density. A mild increase in plasma glucose was seen at medium density, and plasma protein was elevated at medium and high densities. The liver glucose and glycogen content was inversely related to stocking density. The liver triglyceride level was significantly elevated at the highest density, and the ,-amino acid content decreased at the highest density. In muscle, glucose levels were significantly higher in fish kept at the lowest density; the ,-amino acid content was elevated in fish kept at high density. In conclusion, plasma cortisol levels indicated an increasing stress level depending on the culture density, but significant changes in energy reserves did not occur in tissue (mainly liver and muscle glycogen and glucose reserves were significantly affected). [source]