Resistance of two Nile tilapia, Oreochromis niloticus (L.) strains exposed to a mixture of zinc, cadmium and inorganic mercury

Two strains of one month-old Oreochromis niloticus namely CLSU (obtained from Central Luzon State University, Philippines) and NIFI (from National Inland Fisheries Institute, Thailand) were exposed to a sublethal mixture of 1.0 mg L-1 Zn, 0.1 mg L-1 Cd, and 0.01 mg L-1 Hg for two months in aquaria. Another set served as control with only BFS tapwater in the aquaria. At the end of the exposure period the fish were grown for another 2 months in net cages in Laguna de Bay. During the exposure (aquarium) and grow-out (lake) phases, the uptake and elimination of the metals were determined by AAS. Accumulation of the metals peaked at 13.9 µg g-1 Hg, 78.5 µg g-1 Cd, and 1447.0 µg g-1 Zn for NIFI and 14.2 µg g-1 Hg, 82.4 µg g-1 Cd, and 1591.3 µg g-1 Zn for CLSU lost 94.9% Hg, 98.76% Cd, and 89.99% Zn after two months in the lake. After the grow-out period, 2 females and 1 male of each strain were stocked in replicate polyethylene tanks. Time to first spawning, spawning frequency, fry production, and fry survival (after 30 days) were monitored. Results showed no significant effect of treatment and strain with respect to time to first spawning, spawning frequency, and mean fry survival. There was also no significant difference between the treatment and strain in mean fry production when dam weight was used as a covariate in the analysis. The results suggest that both strains of O. niloticus are resistant to long-term exposure to the metals. In addition, the elimination of the metals during the grow-out phase may have also diminished their effect on the breeders of the two strains

Species and proximate composition of Laguna de Bay phytoplankton cultured in three different nitrogen-phosphorus ratios and their utilization by Nile tilapia

Abstract only.Natural phytoplankton populations from Laguna de Bay were used in outdoor batch culture experiment in 1-ton capacity circular concrete tanks and 60-liter glass aquaria for a maximum duration of 72 days. The treatments consisted of the following nitrogen-phosphorus ratios: 2N: 1P, 6N: 1P, and 12N: 1P. The growth and species composition of phytoplankton were monitored in each of the three treatments. The phytoplankton were partially harvested at weekly intervals. The proximate composition of the freeze-dried harvest was also analyzed. The freeze-dried harvest was also used to feed Nile tilapia Oreochromis niloticus (L.) to determine effects of the different N-P ratios on the utilization of phytoplankton by fish. The fish were fed isonitrogenously and ration ranged from maintenance requirement for the first week to 3 times maintenance requirement for the succeeding weeks. Results showed that green algae, particularly the Chlorococcales group, dominated all the cultures. This was followed by diatoms. The blue-green algae consisted the third group in all treatments. Gross energy, crude protein, crude fat, neutral detergent fiber and crude ash content of the phytoplankton harvest did not vary significantly among treatments. However, crude protein expressed as percentage of organic matter was significantly higher in the treatment using 12N: 1P compared to those cultured in lower N-P ratios. Nile tilapia fed phytoplankton from 12N: 1P and 6N: 1P ratios showed significantly better growth than those fed with phytoplankton cultured in the lowest N-P ratio

Survival and heavy metal accumulation of two Oreochromis niloticus (L.) strains exposed to mixtures of zinc, cadmium and mercury

Two Nile tilapia strains of Oreochromis niloticus (L.) (Cichlidae, Teleostei) fingerlings were exposed to mixtures of zinc, cadmium and mercury. The two strains used were Chitralada or NIFI (originally from the National Inland Fisheries Institute, Thailand) and CLSU (from the Freshwater Aquaculture Center of the Central Luzon State University, The Philippines). Short-term (10 days) exposure to a metal mixture of 5 mg 1−1 zinc (Zn), 0.5 mg 1−1 cadmium (Cd) and 0.02 mg l−1 mercury (Hg) gave significantly higher survival percentage in the NIFI strain compared with the CLSU strain. Similar exposure conditions using larger and older fingerlings of the two strains also showed a slightly higher survival percentage in the NIFI strain but the difference was not significant. Prolonged exposure of the fingerlings to a lower concentration of the metal mixture (1.0 mg l−1 Zn, 0.1 mg l−1 Cd, 0.01 mg l−1 Hg) also resulted in similar survival percentages between the two strains at the end of the 60 days run. Whole body accumulation of Zn was significantly higher in CLSU than in NIFI after 14-day exposure to the low concentration metal mixture. There was no significant difference in the accumulation of Cd and Hg between the two strains. Of the three metals, Hg had the highest bioaccumulation factor (BF) which was ∼900–1000, followed by Cd with 255–280 and Zn with 180–195 times the nominal concentration in the water. Concentration of Cd and Hg in fish tissues increased with exposure period while the concentration of Zn was maintained in NIFI and decreased in CLSU between the 6th and 14th day of exposure, suggesting that Zn (an essential element) accumulation maybe regulated by both strains

Acute toxicity of mercury to Oreochromis niloticus fingerlings

Fingerlings of Oreochromis niloticus were exposed to the following mercury (as HgCl2) concentrations: 0.005, 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06 mg l-1 Hg of water. Hyperactivity and erratic swimming were the first indications of mercury intoxication. Scoliosis, a curvature in the mid-trunk region, was observed in some fish in the 0.03 - 0.06 mg l-1 Hg tanks. The occurrence of scoliosis is significantly correlated with mercury concentration. The 24 hour LC50 (0.0375 mg l-1 Hg) did not differ significantly with the 96 hour LC50 (0.0350 mg l-1 Hg)

Effects of long-term exposure to a mixture of cadmium, zinc, and inorganic mercury on two strains of tilapia Oreochromis niloticus (L.)

Tilapia are an economically important group of fish. They have a short generation period of 3-6 months, and exhibit successive breeding. In addition, their fast growth, herbivorous or omnivorous feeding habits, high food conversion efficiency, ease of spawning, ease of handling, resistance to disease and good consumer acceptance make this group of fish highly popular in aquaculture in Asia, Africa and other developing countries. Tilapia have been the subject of research on pollution effects over the last decade. The purpose of this study was to determine growth, accumulation and depuration responses of 2 strains of the Nile tilapia, Oreochromis niloticus, chronically exposed to a mixture of heavy metals including cadmium, zinc and mercury

Accumulation and tissue distribution of radioiodine (131I) from algal phytoplankton by the freshwater clam Corbicula manilensis

Radioactive wastes discharged from establishments involved in the use of radioisotopes such as nuclear powered industries, tracer research and nuclear medicine are a potential public health hazard. Such wastes contain radionuclides, particularly Iodine-131 (131I), produced in fission with a yield of about 3%. It is a beta emitter (Bmax = 0.61MeV); it also emits gamma photons. It has a short half-life (8.04 d) (Dutton 1975), hence it is difficult to detect unless accumulated by indicator organisms. Radionuclides in waste waters are known to be taken up by molluscs such as mussels (Van der Borght and Van Puymbroeck 1970; Fowler et al. 1975; Hetherington et al. 1976; Helt et al. 1980; and Sombrito et al. 1982), oyster (Romeril 1971; Cranmore and Harrison 1975) and clams (Cuvin and Umaly 1988). This study aims to determine the uptake of 131I from algal phytoplankton (Choroococcus dispersus) fed to the freshwater clam Corbicula manillensis as well as the organ/tissue distribution. The results will be compared with our previous study on 131I uptake from water by the same clams (Cuvin and Umaly 1988)

Bacterial microbiota of hatchery-reared freshwater prawn Macrobrachium rosenbergii (de Man, 1879)

Quantitative and qualitative analyses of bacterial microbiota associated with hatchery of freshwater prawn Macrobrachium rosenbergii (de Man, 1879) were conducted over three larval cycles, along with important water quality parameters. Physicochemical parameters (temperature, DO, salinity, pH and total ammonia) of culture water were within the optimum level required for the hatchery phase of M. rosenbergii. Aerobic plate count (APC) (log10 CFU.mL-1) ranged from 4.2 ± 0.18–8.7 ± 0.01 in rearing water and (log10 CFU.g-1) 3.3 ± 0.12–9.1 ± 1.1 in eggs and larvae. Significant differences in APCs among larval stages were observed. Ten genera and 17 species were identified with the predominance of Gram-negative bacteria constituting 63 % of all isolates (n = 706). Acinetobacter baumannii, Acinetobacter lwoffii, Chryseobacterium indologenes, Enterobacter aerogenes, Enterobacter cloacae, Vibrio furnissii, Vibrio cholerae non-01, Plesiomonas shigelloides, Pseudomonas aeruginosa, Pseudomonas pseudoalcaligenes, Bacillus cereus, Staphylococcus haemolyticus, Staphylococcus warneri and Staphylococcus xylosus were predominantly present in culture water. These bacteria likewise dominated in eggs and larvae except for the absence of Ps. aeruginosa, Ps. pseudoalcaligenes, V. cholerae non-01, Staphylococcus epidermidis and Staph. xylosus in eggs, clearly indicating that resident bacteria in water affect the composition of bacteria in eggs and larvae. Some of these are opportunistic pathogens. Thus, control measures to reduce influx of pathogenic microbes in the system by maintaining good water quality and good farm management practices through disinfection of culture facilities, rearing water, Artemia cysts, the practice of good hygiene of personnel, regular water exchange and feed regulation among others and cautionary use of antibiotics can be adopted

Bacterial microbiota of hatchery-reared freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and their pathogenicity

Quantitative and qualitative analyses of bacterial microbiota associated with hatchery of Macrobrachium rosenbergii (de Man, 1879) were conducted over three larval cycles, along with important water quality parameters. Physicochemical parameters (temperature, DO, salinity, pH, and total ammonia) of culture water were within the optimum level required for the hatchery phase of M. rosenbergii. Significant differences in aerobic plate count (APC) among larval stages were observed. Ten genera and 17 species were identified with the predominance of Gram-negative bacteria constituting 63 % of all isolates (n = 706). A total of 17 dominant bacterial isolates randomly selected from freshwater prawn larvae were screened for in vitro hemolysin activity using blood agar plate (BAP) medium with 5% sheep blood. Pathogenicity of the isolated bacterial strains was assessed through in vivo infection bioassay. Out of the 17 isolates tested, six isolates showed α – β zone of hemolysis on the BAP, i.e., Aeromonas caviae, Bacillus cereus, Plesiomonas shigelloides, Staphylococcus warneri, Vibrio cholerae non-01, and Vibrio furnissii, were used in the infection bioassay. The current data indicate that the six bacterial isolates tested, particularly B. cereus and V. cholerae non-01, are opportunistic pathogens capable of inducing disease epizootics, particularly in freshwater prawn hatcheries with suboptimal rearing water conditions. Thus, control measures to reduce the influx of pathogenic microbes in the system by maintaining good water quality and good farm management practices through disinfection of culture facilities, rearing water, and Artemia cysts, the practice of good hygiene of personnel, regular water exchange, and feed regulation, among others, and cautionary use of antibiotics, can be adopted