Browsing by Author "Cuvin-Aralar, Maria Lourdes A."
ArticleMLA Cuvin-Aralar -
Lakes and Reservoirs: Research & Management, 2016 - WileyLaguna de Bay is the largest inland water body in the Philippines, being used predominantly for aquaculture and open water fisheries. Aquaculture in the lake began decades ago, with many changes in the lake ecosystem having occurred since that time. Most dominant species for fish culture are introduced species. Other invasive species were also introduced to the lake as escapees from land-based aquaculture facilities. This study was conducted to monitor fish diversity in two adjacent, but distinctly different, sites in the lake, namely an open fishery area (OFS), with no adjacent aquaculture structures, and an aquaculture site (AQS), with cages for the culture of various commodities. Fish traps were installed at both sites, with the traps being sampled at least every 2 weeks from April 2013 to February 2015. The results of pairwise t-tests indicated significantly higher Shannon–Wiener diversity index (H′), evenness (J′), Simpson's similarity index (D) and species richness (s) in OFS than in AQS. In terms of total catch per day, significantly greater fish biomass were obtained from AQS than from OFS. Introduced aquaculture species had a mean dominance of 83% and 47% in AQS and OFS, respectively. However, invasive species introduced from the ornamental fish trade exhibited a mean relative dominance of 10.3% in AQS and 13.5% in OFS. The relative dominance of native species was also significantly higher in OFS (41%) than in AQS (6.5%). The results of this study demonstrated the adverse impacts of aquaculture in regard to the species diversity of fish in localized areas in Laguna de Bay. The dependency of aquaculture on introduced fish species adversely impacted the natural fish population in the lake. Focusing on the culture of commercially important local species for aquaculture, rather than introduced species, will improve fish production of inland waters without accompanying adverse impacts on biodiversity.
Resistance to a heavy metal mixture in Oreochromis Niloticus progenies from parents chronically exposed to the same metals Adult Oreochromis niloticus were mass spawned in concrete tanks. The one-month old progenies (F1) 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 (F2) of the exposed F1 (EF1) 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 F2 from unexposed F1 (UF1) received the same treatment. Results showed that in both exposure systems, survival of the F2 of EF1 was significantly higher (P<0.05) than those from UF1. The medial lethal time (LT50) of the F2's were estimated from the time-response curve following regression analysis: 5.16 days (F2 of UF1) and 9.03 days (F2 of EF1) in the static exposure experiment; 3.34 days (F2 of UF1) and 5.52 days (F2 of EF1) 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.