Julio Vicente Lombardi

Hematological parameters in Nile Tilápia, Oreochromis niloticus exposed to sub-letal concentrations of mercury

Mercury toxicity in tilapia, Oreochromis niloticus, (Linnaeus, 1758) was investigated by the hematological parameters after long-term (14 days) exposure to various Hg concentrations (0.02, 0.002, 0.0002mg/L Hg). Test groups were set up with three replicates for each concentration, plus the control group. Blood samples were collected from six individuals for each concentration at 0, 3, 7, 10 and 14 days of exposure. The hematological parameters analyzed were: total red blood cell count (RBC), hemoglobin concentration (Hb), hematocrit (Ht), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), total white blood cell count (WBC) and differential leukocyte counts and total thrombocyte count (Tr). There were no significant differences among the mean hematological values at the different Hg concentrations indicating that Hg at the concentrations studied was not toxic to tilapia.

Stocking densities for nursery phase culture of the freshwater prawn Macrobrachium rosenbergii in cages

Abstract Effect of stocking density on growth, biomass increase and survival of postlarvae of Macrobrachium rosenbergii were evaluated in cages fixed inside an earthen pond. In the primary nursery phase, newly metamorphosed postlarvae (PL) were stocked for 20 days at densities of 2, 4, 6, 8 and 10 PLs l −1 . In the secondary phase (60 days), the densities tested were 100, 200, 300, 400, 600 and 800 PLs m −2 . Prawns were fed with a 35% protein commercial pellet. Survival, final mean weight and average weight gain were significantly lower ( P P P P −2 than for density of 800 m −2 . Biomass increase was significantly higher ( P 0.01) at densities of 400, 600 and 800 PLs m −2 , when compared to densities of 100 and 200 m −2 , whereas survival differences were not significant. High-density nursery culture of M. rosenbergii in cages seems to be feasible, in order to reduce the costs normally found in conventional nursery systems.

Compensatory growth of Malaysian prawns reared at high densities during the nursery phase

Este trabalho foi realizado com o objetivo de verificar a ocorrencia de crescimento compensatorio em camaroes-da-malasia (Macrobrachium rosenbergii) cultivados em cercados, apos serem estocados em gaiolas sob altas densidades durante a fase de bercario. O experimento foi conduzido em gaiolas com 0,5 m2 e cercados com 2 m2 instalados em um viveiro de fundo natural com 2.400 m2. Pos-larvas (PL) de camaroes com peso medio de 0,026 ± 0,012 g (fase de bercario) foram inicialmente estocadas em 16 gaiolas, nas densidades de 50, 400, 800 e 1.200 camaroes m-2. Apos 60 dias, os camaroes foram transferidos para 16 cercados de engorda, na densidade de 12 camaroes m-2. O peso medio inicial dos camaroes nessa fase foi o peso medio final registrado na fase de bercario, como segue: 50 PL m-2 = 2,3 ± 0,3 g; 400 PL m-2 = 0,5 ± 0,03 g; 800 PL m-2 = 0,3 ± 0,05 g e 1.200 PL m-2 = 0,1 ± 0,01 g. Racao comercial para camaroes (35% de proteina) foi fornecida uma vez por dia, ao entardecer. Apos 244 dias, a sobrevivencia, o peso medio e a biomassa nao diferiram significativamente entre as densidades de cultivo. A taxa de crescimento relativo foi significativamente maior nos camaroes previamente estocados a 1.200 PL m-2 e a eficiencia da conversao alimentar, significativamente melhor para aqueles previamente estocados a 400 e 1.200 PL m-2. Esses resultados sugerem a existencia de crescimento compensatorio parcial em M. rosenbergii, o que pode viabilizar a estocagem de camaroes dessa especie em altas densidades na fase de bercario.

Eutrophization process in a system used for rearing the nile tilapia (Oreochromis niloticus), São Paulo State, Brazil

Aquaculture is composed of various themes of interest, particularly does eutrophization due to feeding have direct effects on fish ponds and the whole aquatic system. This study focused on the study of the water quality of an aquatic system related to Nile tilapia (Oreochromis niloticus) rearing. Sampling was done at six sites during one rearing cycle (six months), taking water from the source of water supply, the fish pond itself, the effluent of the fish pond and the mixed waters. A principal component analysis revealed that, among all the environmental variables analyzed, chlorophyll-a, total nitrogen and phosphorus and organic matter were responsible for the variations observed during the rearing cycle. Other sources of variability extrinsic to the fish pond make it evident that the assessment must take the entire aquatic system related to the rearing into consideration, minimizing negative effects.

Potassium chloride and sodium chloride as reference toxicants to assess quality of toxicity tests carried out with the microcrustacean cladocera Ceriodaphnia dubia

Two reference toxicants (potassium chloride-KCl and sodium chloride-NaCl) were used in the present study in order to assess the sensitivity of the microcrustacean cladocera Ceriodaphnia dubia. Chronic toxicity tests were carried out with those two salts and the sensitivity expressed as IC50;7D concentration that causes inhibition of 50% of reproduction ability, in seven days exposure time. The medium values estimated for IC50;7D were 200.70 and 499.60 to KCl and NaCl, respectively. Those data have demonstrated that KCl can be more restrictive and more suitable than NaCl, when used as standard reference toxicant for plotting control charts of sensitivity.

Toxicidade Aguda do Mercúrio, Associado ao Selênio, para Alevinos de Tilápia Oreochromis niloticus...pp. 243-248

Acute toxicity of mercury associated to selenium, to minnows tilapia Oreochromis niloticus The aim of this study was to evaluate if the two forms of selenium (sodium selenite – Se 4+ and sodium selenate – Se 6+ ) have antagonistic effect on the acute action of mercury chloride (HgCl 2 ) by toxicity acute tests, using minnows of tilapia, Oreochromis niloticus as test-organisms. The treatments consisted of: I) control group; II) only Hg; III) only Se 4+ ; IV) only Se 6+ ; V) Se 4+ + Hg; and VI) Se 6+ + Hg. The following concentrations were used in the test: 0.4 mg L –1 of Hg (considered as lethal median concentration – LC 50 ) and 1.0 mg L –1 of Se (considered as non lethal effect concentration – NOEL) for two selenium forms. After 24 hours of exposition to the treatments that contained mercury, the fish presented clinical signals of poisoning, such as: hyperactivitiy, skin darkness, swimming disorder, difficulty for breathing, and death. There were no differences statistically significants (p > 0.05) in the mortality between the treatments II-V, and II-VI, indicating the absence of antagonistic effect between these elements. Results discussed in this paper suggest that the concentration of Se (NOEL) used in the present study perhaps has exceeded the molecular ratio of 2.5 : 1/(Hg : Se) supposedely considered as suitable for interacting atagonisticaly in the toxicity of mercury.