Abundance and Composition of Zooplankton (Copepoda, Cladocera, Rotifera) in Lake Taal: Potential Impact of Intensive Size-Selective Predation by the Freshwater Sardine, Sardinella tawilis (Herre 1927)

Zooplankton are considered to be important members of the lake ecosystem. The abundance and composition of which are due to several factors, for example, the impact of intensive size-selective predation by planktivorous fishes residing in the lake. In this study, the abundance and composition of zooplankton found in the vicinity of Isla Napayun - a known fishing ground of the freshwater sardine, Sardinella tawilis (Herre 1927) was analyzed using samples taken from vertical plankton tows from the 10 and 20 m depths in 2 sampling sites from the said area. These were then compared with the stomach contents of S. tawilis taken during the same period. Results show that there were 4 genera of Copepoda, 4 genera of Cladocera and 2 genera of Rotifera found in the plankton tows that were analyzed. Of these, the nauplius larvae of the copepods were noted to be the most abundant followed by the rotifer Brachionus spp. Analysis of the stomach contents of the collected S. tawilis samples revealed a zooplankton diet that was composed of 90% Copepoda with the remaining 10% being made up of the Cladocera and Rotifera. These results indicate that small-bodied organisms dominate the lake. This is indicative of intensive size-selective predation by the S. tawilis on the zooplankton population of the area. This is further validated by the high preference of S. tawilis for Copepoda, which is the largest of the 3 groups (in terms of size) in the samples that were analyzed in spite of the fact that small-bodied zooplankton dominate the zooplankton community during the entire sampling period. The zooplankton found in this particular area of Lake Taal has been observed to be highly influenced by intensive size selective preference of planktivores such as the S. tawilis for bigger zooplankton

Abundance and Composition of Zooplankton (Copepoda, Cladocera, Rotifera) in Lake Taal: Potential Impact of Intensive Size-Selective Predation by the Freshwater Sardine, Sardinella tawilis (Herre 1927)

Zooplankton are considered to be important members of the lake ecosystem. The abundance and composition of which are due to several factors, for example, the impact of intensive size-selective predation by planktivorous fishes residing in the lake. In this study, the abundance and composition of zooplankton found in the vicinity of Isla Napayun - a known fishing ground of the freshwater sardine, Sardinella tawilis (Herre 1927) was analyzed using samples taken from vertical plankton tows from the 10 and 20 m depths in 2 sampling sites from the said area. These were then compared with the stomach contents of S. tawilis taken during the same period. Results show that there were 4 genera of Copepoda, 4 genera of Cladocera and 2 genera of Rotifera found in the plankton tows that were analyzed. Of these, the nauplius larvae of the copepods were noted to be the most abundant followed by the rotifer Brachionus spp. Analysis of the stomach contents of the collected S. tawilis samples revealed a zooplankton diet that was composed of 90% Copepoda with the remaining 10% being made up of the Cladocera and Rotifera. These results indicate that small-bodied organisms dominate the lake. This is indicative of intensive size-selective predation by the S. tawilis on the zooplankton population of the area. This is further validated by the high preference of S. tawilis for Copepoda, which is the largest of the 3 groups (in terms of size) in the samples that were analyzed in spite of the fact that small-bodied zooplankton dominate the zooplankton community during the entire sampling period. The zooplankton found in this particular area of Lake Taal has been observed to be highly influenced by intensive size selective preference of planktivores such as the S. tawilis for bigger zooplankton

Impact assessment of cage culture in Lake Taal, Philippines

Abstract only.The environmental impact of cage culture on water quality of Lake Taal was assessed from March 1996 through February 1997. Three stations were considered namely: Balas, which serves as station 1 (non-cage area) and Sampaloc and Laurel, stations 2 and 3 (cage areas), respectively. Monthly water samples with two replicates were collected using a van Dorn sampler at 0, 5, 10 and 15-m depths in all stations. Below surface water from the inside of the cages was also collected. Water temperature, water transparency, pH, and conductivity were determined in situ. Dissolved oxygen, chloride, NO3, NH3, PO4, and total P were analyzed in the laboratory. Phytoplankton density and algal biomass (through cholorophyll a) and primary productivity indices were determined with the light-and-dark bottle method. Of the water quality parameters, conductivity and DO had significant differences between non-cage and cage areas. Conductivity gave significant difference (P<0.01) between control and cage area during the wet season. Highest conductivity value (2100 µ S/cm) was observed in station 3. Mean values of DO gave significant differences (P<0.05) in the different stations throughout the study period. A decrease of DO to 2.5 mg/1 was observed below 10-m depth around the cage areas. Analysis indicates that cage culture leads to oxygen depletion in the water column. The presence of cage structures decreased the flow rate resulting to weak circulation. The reduced water circulation in effect decreased the supply of oxygen and removal of toxic waste metabolites from the vicinity of the fish farm, and reduced the supply of plankton. These results suggest that the impact of cage culture in Lake Taal is minor but can alter the lake ecosystem if not properly managed. Zoning and continuous water quality monitoring are needed

Lake Taal's freshwater sardines Sardinella tawilis (Herre): Evolutionary insights based on morphological, molecular, and geological data

Sardines (family Clupeidae or herrings) are mostly marine species. In the Philippines, Lake Taal is the habitat of Sardinella tawilis (local name tawilis ), the only local endemic sardine species known to be fully adapted to a freshwater environment. Its evolutionary history is thus of great interest. So far, analyses of morphometric, meristic, isozyme, and mtDNA data point to the marine species Sardinella albella as the closest marine relative. Furthermore, mitochondrial DNA data revealed restricted substitution that may indicate either the beginning of a genetic differentiation of two tawilis sub-populations or the ghost of polymorphism past strengthened by genetic drift. Sardinella tawilis is believed to have emigrated from Balayan Bay to Lake Taal when it was formed in the course of volcanic eruptions some 240 years ago. The data do not, so far, support this contention. An alternative explanation on the speciation of this species is presented here

Anatomy of the Digestive System of Radix sp. (Bassomatophora: Lymnaeidae) from Lake Taal, Batangas

The digestive anatomy of Radix sp. from Taal Lake, Batangas, Philippines, was studied. The major differences with the other known lymnaeids previously described from the Philippines are found in the radular formula, presence of intestinal caecum, the orientation of the pylorus and the intestine, and the number of loops made by the intestine around the stomach and the digestive gland

Low isozyme variation in native and transplanted populations of the endemic Philippine silver perch, Leiopotherapon plumbeus (Kner, 1864) from three lakes in the Philippines

The silver perch, Leiopotherapon plumbeus (Kner, 1864), is an endemic and economically important fish in the Philippines. A native species of Laguna de Bay, the silver perch was transplanted from this lake to Sampaloc Lake in the late 1950s and Taal Lake in the early 1970s. Morphological variation has been observed among the native and transplanted populations of the silver perch. In this study, genetic variation within and between the native and transplanted populations was examined using isozyme electrophoresis. Four sites were sampled: two in Laguna de Bay (Binangonan and Tanay) and one each in Sampaloc Lake and Taal Lake. Twenty-two (22) loci were scored but only one locus (PGM*) was polymorphic by the 95% criterion and only two loci (ADH* and PGM*) were polymorphic by the 99% criterion. The average heterozygosities, genetic distances and FST values of specimens from the four sites were very low, suggesting that the native and transplanted populations had very low genetic variation and that they were genetically homogeneous despite the presence of morphological varia- tion. The low genetic variation could possibly be due to a population bottleneck in the native population in Laguna de Bay in the past and to the low genetic variation of the founders in the transplanted populations

New Philippine record of South American sailfin catfishes (Pisces: Loricariidae)

A taxonomic and biogeographic study of the introduced suckermouth armored catfishes locally known as janitor fish is briefly described. Specimens were collected from five sites in the Laguna de Bay basin and were examined for 19 meristic and 37 morphometric characters and other external features including coloration. Results were compared with existing literature on fishes in the family Loricariidae. Examination revealed that specimens of janitor fish, previously reported as Hypostomus plecostomus, actually belong to the genus Pterygoplichthys, family Loricariidae. Collected specimens consisted of two species-Pterygoplichthys disjunctivus and Pterygoplichthys pardalis. Both species were collected from the five sites except in Pasig River where only P. disjunctivus was collected. Copyright © 2006 Magnolia Press

consensus sequences

Consensus sequences of the COI barcodes of the fishes collected in Taal Lake, Philippine