Maria Lourdes A. Cuvin-Aralar

Microcystins in natural blooms and laboratory cultured Microcystis aeruginosa from Laguna de Bay, Philippines.

Laguna de Bay, the largest freshwater lake in the Philippines, experiences periodic blooms of the cyanobacteria Microcystis aeruginosa. Blooms of these cyanobacteria in 1996, 1998 and 1999 were sampled. HPLC and MALDI-TOF mass spectrometry were used to analyze for microcystins. A total of 16 structural variants of the toxin were isolated from the samples with microcystin LR (MC-LR) as the most abundant variant in the samples from 1996 and 1999 making up 77 to 85% of the total, respectively. MC-RR was the dominant variant in the 1998 bloom making up 38%. The samples from 1996 had the highest total toxin concentration (4049 microg g(-1)) followed by those from 1998 (1577 microg g(-1)) and 1999 (649 microg g(-1)). A strain of M. aeruginosa previously isolated from the lake was also cultured in the laboratory under different nitrogen concentrations (1, 3 and 6 mg L(-1)) and elevated phosphorus concentration (0.5 mg L(-1)) to determine the influence of these factors on toxin production. A total of 9 different structural variants of microcystin were isolated from the laboratory cultures with MC-LR consisting more than 75% of the total in all treatments. No significant differences in the total toxin concentration as well as the % distribution of the different variants among treatments were observed. However, the strain of M. aeruginosa cultured in the laboratory had from 3 to 20 times higher total microcystin than those harvested from the lake.

Tissue distribution of mercury and selenium in minnows, Phoxinus phoxinus

Effect of selenium on the distribution pattern of mercury in a common freshwater fish, the minnow Phoxinus phoxinus (Cyprinidae). Conservely, the effect of mercury on the tissue distribution of selenium will also be studied

Effects of low nitrogen-phosphorus ratios in the phytoplankton community in Laguna de Bay, a shallow eutrophic lake in the Philippines

The effects of low nitrogen-phosphorus ratios on microalgae from a large eutrophic freshwater lake in the Philippines were investigated. Natural microalgal populations from Laguna de Bay, the largest lake in the Philippines, were cultured using three different nitrogen-phosphorus weight ratios (2N:1P; 6N:1P and 12N:1P) at two phosphorus concentrations (0.25 and 0.5 mg l–1) in each case. The growth and genera composition of the cultures under the different treatments were followed for a 12-week period. Community level responses were assessed based on species richness (s), Shannon-Wiener Index (H’), Simpson Index (λ) and Evenness (J’). Among the different microalgal groups, only the chlorophytes showed a significantly higher density in response to the 12N:1P treatment at the higher P concentration, indicating that the nutrient ratio had a significant interaction with the nutrient levels used in the experiments. The genera found in the different treatments were generally similar; however, the degree of dominance of some varied with treatment during the experiment. The succession of dominant genera also differed among the N:P treatments. The diatoms like Fragilaria, Aulacoseira (= Melosira) and Nitzschia dominated the lowest N:P. On the other hand, chlorophytes (Kirchneriella and Scenedesmus) dominated the highest N:P treatment, particularly from the second to the seventh week of the experiments with the diatoms becoming co-dominant only towards the eighth week until the end of the experimental. The 6N:1P treatment showed a mixed dominance between the diatoms and the chlorophyte genera. The various indices of diversity indicate significantly lower diversity only in the 12N:1P at 0.5 mg l–1 P and not in 12N:1P at 0.25 mg l–1 P.

Resistance to a heavy metal mixture in Oreochromis Niloticus progenies from parents chronically exposed to the same metals

Abstract Adult Oreochromis niloticus were mass spawned in concrete tanks. The one-month old progenies (F 1 ) were exposed for two months to a mixture of 0.01 mg L −1 Hg, 0.1 mg L −1 Cd and 1.0 mg L −1 Zn. The survivors were grown to sexual maturity in a natural environment (lake). The fish were spawned and the progenies (F 2 ) of the exposed F 1 (EF 1 ) were exposed to another mixture of the three metals: 3.0 mg L −1 Zn, 0.30 mg L −1 Cd and 0.01 mg L −1 Hg, both in a static and static-renewal system. Another group of F 2 from unexposed F 1 (UF 1 ) received the same treatment. Results showed that in both exposure systems, survival of the F 2 of EF 1 was significantly higher (P 1 . The medial lethal time (LT 50 ) of the F 2 s were estimated from the time-response curve following regression analysis: 5.16 days (F 2 of UF 1 ) and 9.03 days (F 2 of EF 1 ) in the static exposure experiment; 3.34 days (F 2 of UF 1 ) and 5.52 days (F 2 of EF 1 ) in the static-renewal run. Exposure of the parental stock resulted in the culling out of individuals which were more susceptible to the heavy metals. The more resistant members of the population (survivors) which have the ability to adapt to the toxicants were able to pass on the resistance to their offspring. The results are supported by other studies in the field which demonstrate high resistance in populations of organisms living in contaminated sites.

Mercury levels in the sediment, water, and selected finfishes of Laguna Lake, The Philippines

Abstract Monthly samples of sediment, water and commercially important species of fish, primarily Oreochromis niloticus and Chanos chanos , plus a few other species, were collected from the West Bay area of Laguna Lake, The Philippines from January to December 1987. Mercury levels were determined in all samples by cold vapor atomic absorption spectrophotometry. Results showed that sediment samples contained mercury levels ranging from 26.7 to 117 ppb. Mercury levels in water samples were low, ranging from below detectable to 0.5670 ppb. The mercury levels in the water were negatively correlated with conductivity and dissolved oxygen and positively correlated with turbidity. The mercury burden of the fish species samples was below the maximum permissible level set by the WHO and USFDA of 0.05 ppm. No direct correlation was observed between mercury levels in sediment and water, water and fish and sediment and fish.

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 ({sup 131}I), produced in fission with a yield of about 3%. Radionuclides in waste waters are known to be taken up by molluscs such as mussels, oysters, and clams. This study aims to determine the uptake of {sup 131}I from algal phytoplankton (Chroococcus dispersus) fed to the freshwater clam Corbicula manilensis as well as the organ/tissue distribution. The results will be compared with a previous study on {sup 131}I uptake from water by the same clams.

Embryonic development of the Caridean prawn Macrobrachium mammillodactylus (Crustacea: Decapoda: Palaemonidae)

The freshwater knob-tooth prawn Macrobrachium mammillodactylus is a commercially exploited species in the Philippines. To study the biology of this species, broodstock from the wild was collected, transported to the laboratory and kept in pairs in indoor polyethylene tanks for breeding. Eggs from berried females were sampled to follow the stages of embryonic development until hatching to zoea larva. It took 18.0 ± 2.1 days for the eggs to hatch at ambient water temperature between 25 and 28 °C. The morphological landmarks of development at the different stages (pre-cleavage, cleavage, blastula, pre-nauplius, post-nauplius and pre-hatching) of the live embryos are described. Incremental percentage staging was adopted from 0% at fertilization to 100% at hatching and were matched with corresponding morphological development. Egg volume increased significantly toward the mid-to-later stages of development. The eye index also showed a significant increase as the egg developed. The colour of the egg mass changed from light olive green to grey as the eggs progressed in development. The general pattern of development was comparable to other members of the genus Macrobrachium.