Nine concrete tanks (2 x 2 x 1 m) were stocked with tilapia fingerlings (abw = 3.3±0.9 g) and three stocking rates (50 fish/m², 100/m², and 150/m²) were tried. The rearing period lasted for 120 days. Fingerlings were fed commercial diet containing approximately 27% crude protein. The amount of feed was adjusted based on monthly weight samplings. Pre-filtered lake water pumped through gravity aerators into the tanks was used throughout the culture period. Although production was intensified, water agitators and similar mechanical implements were not employed to cut production costs. Results show that tilapia stocked at 50/m³ grew significantly heavier at 109.2 ± 8.0 g. This was significantly better (P<0.05) than fish stocked at 100 and 150/m³, which had basically the same final weight of 82.4 ± 1.8 g and 83.4 ± 8.7 g, respectively. Likewise, survival or recovery at harvest was highest at 92.8% for the stocking rate of 50 fish/m³. The results suggest that stocking at lower densities would result to bigger fish but a lower total yield per tank, or higher stocking densities would mean higher yield but smaller individual fish size at harvest. The rate of water flow through at harvest time was equivalent to 0.30 L/min/kg biomass at the highest stocking density of 150/m³, 0.40 L/min/kg biomass at 100/m³, and 0.60 L/min/kg biomass at the lowest density of 50/m³. Siddiqui et al. (1991) suggested a minimum of 0.50 L/min/kg biomass flow rate for intensive culture of tilapia, but this was generally for clean culture water, not like lake water whose quality varies naturally. After determining the optimum stocking density, a second experiment using bigger fingerlings (57.5±12.6 g) was conducted for 101 days to determine the ideal water flow rate in the system. Varying flow rates (10 liters per minute (Lpm), 15 Lpm and 20 Lpm) were evaluated at a fixed stocking density of 50 fish/m³. Feed ration was 5% during the first two months, 4% on the third month, and 3% thereafter. Tilapia size at harvest increased with increasing flow rate when stocked at 50 fish/m³. From an initial stocking size of 57.5 ± 12.6 g, biggest fish harvests were obtained in tanks with a flow through rate of 20 Lpm (152.2 ± 15.1 g) after 101 days of culture. However, this was not significantly different to fish grown in tanks at 15 Lpm (139.9 ± 7.6 g). Smallest fish harvests were obtained at 10 Lpm at 111.20 ± 8.3 mm. A similar trend was observed with fish length at 157.7 ± 15.5 mm, 150.8 ± 11.0 mm, and 142.1±17.6 mm for 20 Lpm, 15 Lpm, and 10 Lpm, respectively. Feed conversion ratio (FCR) ranged from 1.7 to 2.5 in all treatments. The rate of water flow through at harvest time was equivalent to 1.2 L/min/kg biomass at 20 Lpm, 0.6 L/min/kg at 15 Lpm (sufficient for Laguna de Bay water), and 0.4 L/min/kg at 10 Lpm flowrate. Except for a slight increase in ammonia levels (maximum 1.1 mg/L total ammonia nitrogen) towards the final two weeks of the rearing period, water quality in the culture tanks was generally within tolerable levels throughout the run. Thus, the quality of water from Laguna de Bay can safely support the stocking density used in the experiment. However, if stocking density is further increased, aeration may need to be provided because very low early morning dissolved oxygen levels (DO) were observed, especially in tanks with high stocking density. The significant amount of sludge, mainly fish feces and uneaten feeds, effectively trapped and collected from the settling apparatus, clearly demonstrated the apparatus efficiency. Effluent water was practically rid of solid wastes, and gravity aeration oxygenated the water before it was discharged back to the lake. Ammonia, pH and DO levels of the effluent water were similar to those recorded from the water in the header tank.

An assessment and impact analysis of the fish cage arming in Lake Bato was conducted from October 1999 to January 2000 through a field survey and personal interviews with fish cage farmers, operators and key informants in 10 lakeside communities bordering Lake Bato. Tilapia fish cage farming was the most dominant activity undertaken in the lake owing to its economic contribution and performance. It is sad to note, however, that the management and protection of the lake has been neglected. Results showed that the lake is experiencing serious stress and degradation as a result of fish cage congestion numbering to more than 21,820 units indiscriminately installed all over the lake. The same is also the cause of conflicts (i.e., marginalized small-scale fishers, obstruction of navigational route, and proliferation of dummy fish cage operators) among lake users. As a consequence of expanded technology application, slow fish growth, algal bloom, fish kill, and the apparent shallowing of the lake have become alarming concerns among resource users. It is also worth noting that the industry s sustainability is now under serious threat if not properly planned, managed, and protected. It is therefore recommended that alternative policy and management options be institutionalized. This would include formulation of a lake-wide inter-Local Government Unit (LGU) fisheries ordinance, implementation of Lake Bato Resource Management Plan, organization of a lake-wide fish cage farmers and operators, conduct of collaborative and interdisciplinary research and development initiatives, conduct of technical and management training for Best Fish Cage Practice, and massive information-education-communication (IEC) for concerned municipalities.

Lake Bato is one of the most important lakes in the Bicol Region in terms of economic benefits to lakeshore communities. It is considered a commercial fishing ground of endemic and indigenous fish species. However, fish production in the lake is declining and now under serious threat. This paper is the result of a preliminary survey on freshwater prawns conducted in July 2001 which could serve as a basis in policy formulation for management and conservation measures to attain sustainability. The fishing gears used in catching prawns in Lake Bato are prawn pot bubo , seine net, and prawn shelter. Two species of Palaemonid prawns were noted in the area but the dominant species was Macrobrachium idella, locally known as buyod . It was reported that M. idella is caught year-round but peak season is observed during summer. Based on samples measured, males of M. idella were larger than females. Fisherfolks reported that berried prawns are observed throughout the year but peak season is noted in March to April. The average prawn catch during the survey is 13 kg/fisherfolk/day with an estimated production of about 0.646 MT/day is sold in local and export markets. The average gross income is about P520.00 to P780.00/fisherfolk/day and an estimated total gross income of P26,000.00 to P32,000.00/day. Major issues/ problems related to capture fisheries in the lake are the following: deteriorating habitat, overfishing, and the absence of a management plan.

The demand for fish protein in the Philippines cannot be met by capture fisheries alone so the Philippine government has turned to aquaculture as an alternative source of fish protein. Aquaculture has promoted the introduction of aquaculture species where, although contributing significantly to aquaculture production, has also led to the introduction and establishment of species in local ecosystems through their escape to the wildlife. In the Philippines, freshwater ecosystems with relatively high endemism have become a significant problem. There have been 157 species introduced into the Philippines, 36 of which have been established in the wild. Although most were introduced by the ornamental industry, 79% (23 of 29) of those introduced for aquaculture purposes have established in the wild. After habitat destruction, introduced species are considered the greatest cause of the loss of biological diversity, posing as a major threat to native fishes. Introduced species, however, are also responsible for contributing much to world aquaculture production where over 2.35 million MT (13% of total) were contributed by introduced finfish species to freshwater aquaculture production in 2000. The Philippines is the 8th freshwater aquaculture producer in the world with 111,764 MT produced in 2000, approximately 75% of which were contributed by introduced species. Documenting the introduction (man-made or otherwise) of exotic fishes provides a general view of the magnitude of these movements, their existence in the wild and the existing and potential threat faced by the ecosystems to which they have been introduced. Tracking the impact of the introduced fishes into ecosystems should be treated with very high importance. Currently, this kind of information is either not available, very limited, or scattered in different journals and agency/project reports. FishBase provides a shell to document and consolidate specific information on the occurrence and impact of species in the ecosystems where the species are now found. A registry like this provides information about the status of the introduced and native species as well as current or potential threats to the ecosystems. Together and through links to other related information sources on the web, information can thus be accessed easily. The fusion of all these information sources would allow students, researchers, decision- and lawmakers to access updated and reliable information for programs, projects and aquatic resources conservation and management.

Yearlong assessment of the artisanal fishery from the three floodplain lakes of Ticgon, Dinagat, and Mihaba in Agusan Marsh, a declared national priority protected area, was done using length-weight frequency analyses. Results showed that the catch on economically-important fishes such as Cyprinus carpio and Trichogaster pectoralis in Lakes Ticgon and Mihaba did not suggest growth overfishing. The regulated mesh size allowed in the area is, to some extent, effective. However, Oreochromis niloticus and Trichogaster pectoralis caught from Lake Dinagat were found to have sizes below the optimum and with size less than its length at first maturity. This assessment has a very profound implication to the conservation efforts in the area considering that fishery in the marsh is a cheap source of protein for the local communities. Yet, the continuity of the said regulations remains a formidable challenge for some reasons: community in the marsh is dispersed; the area is so vast with lots of entry and exit points making monitoring a tedious and expensive job; and unabated electrofishing, although declared an illegal activity, is still more profitable than mere use of fishing gears.

The bottom topography and vertical temperature profile of Lake Mainit was assessed to provide baseline data to understand the dynamic behavior of the lake as an ecosystem. Many limnological phenomena, distribution of biota, and productivity were directly related to the morphological features of the lake basin. The bottom topography was assessed using echo sounding method. Vertical temperature profile of the lake was evaluated using reversing thermometers mounted on Nansen reversing samplers. All data points were marked by geographic positioning system. Results indicated that the maximum recorded depth was 218.75 m based on current surface elevation of Lake Mainit. The deep portions of the lake with steep shoreline profile were observed in the vicinity along the Malimono ridge. Areas in the lake with more than 200 m depth were observed between Bonga and the islets of Kitcharao. Coasts along Mainit and the eastern part of the lake, except the Kitcharao Park which is rocky, have sloping shoreline. The vertical temperature profile of Lake Mainit ranged between 26.55° - 30°C. The thermocline layer was observed between 10 m to 40 m. The variation in vertical temperature was observed at the surface and at levels down to a depth of 30 m. Beyond 30 m, there was a minute variation of temperature that ranged between 0.03° - 0.15°C.

In a span of seven years, three catastrophic flood events ensued from the breakout of two crater lakes: two from Maughan Lake, the crater lake of Parker volcano, and one from Pinatubo volcano. The mechanisms of the three lake-breakouts differ significantly from each other. In September 1995, about 30 million m³ of water was suddenly released from Maughan Lake, resulting in large life and property losses. The breakout, which lowered the lake level by 10 m, was caused by the sudden removal of the material that had been damming the lake at its outlet along the Gao Creek. How the dam material was removed remains the subject of a criminal investigation. A result of the 1995 breakout was the destabilization of the slopes along the Gao Creek, which resulted in several large landslides that dammed the lake outlet anew. By January 1997, Maughan Lake had risen by more than 8 m, equivalent to an additional 24 million m³ of water. Maughan Lake broke out again in March 2002, hours after a M6.8 earthquake occurred offshore southwest of Cotabato City. The lake level was lowered by more than 9 m, and the total volume of water released was about 27 million m³. The debris flows and floods resulting from the breakout emplaced deposits that could be traced to at least 80 km along the Gao-Alah River. The breakout is believed to have been caused by the progressive weakening of the landslide dam due to the earthquakes, and/or to seiches that may have been produced along the blocked Gao Creek. The lake-breakout scenario at Pinatubo was anticipated as early as 1998, with the lake rising at ~10 m per year. Judging from the loose emplacement and low density of the uppermost layers of the deposits at the Maraunot Notch (the lowest part of the crater rim), Philippine Institute of Volcanology and Seismology (PHIVOLCS) and United States Geological Service (USGS) scientists predicted a potentially large lake-breakout lahar event that might inundate the town of Botolan, Zambales. In September 2001, while the lake was still 5 m below spilling level, the government decided to excavate a trench that would drain the lake at a scheduled time and prevent the accumulation of an additional 15 million m³ of water. However, miscommunication between scientists and engineers resulted in a trench that favored slow drainage of the crater lake. It was only in July 2002, during heavy typhoon rains, that the lake actually broke out, releasing about 65 million m³ of water and lowering the lake by 23 m. The floodwaters bulked up with sediments downstream to form lahars with a total volume of 165 million m³, reaching the Bucao Bridge but sparing the Botolan town proper. Without the 2001 trenching, the lahar volume could have been more than 200 million m³, perhaps enough to adversely affect Botolan. The 2002 Pinatubo crater-lake breakout was probably generated by channel-bed erosion at the Maraunot Notch, as predicted by commonly used dam-breach models. With the lake now draining through the Maraunot Notch over erosion-resistant dacitic bedrock, a catastrophic breakout by such mechanism is no longer expected. Lake-breakout, however, may be triggered by unpredictable events such as an eruption from the crater.

Lake Manguao is the only freshwater lake in mainland Palawan. It is special because it has no surface outflow that connects it to the sea. The fish fauna of Lake Manguao was studied during three sampling events in June, September, and November 2002. Seven types of fishing gears were used and a total of eight stations were sampled representing both the littoral and open water zones of the lake. The study assessed whether the unique fish fauna first catalogued by Day (1914) and later by Davies and Green (1990) is still present in the lake after the introduction of Oreochromis niloticus (Nile tilapia) in 1992. The study also looked into the local uses of the lake fishes. A total of 12 fish species from ten genera belonging to eight families including Anabantidae, Channidae, Cichlidae, Clariidae, Cyprinidae, Eleotridae, Hemiramphidae, and Siluridae were collected from the lake. In addition to the species previously accounted for by earlier researchers, two new fish species were recorded: Clarias macrocephalus, a native catfish of the Philippines; and Puntius sp., a possibly undescribed lake-endemic cyprinid. The study also provides answer to the argument brought up by Davies and Green (1990) stating that there is only one endemic species of Puntius in the lake contrary to the accounts of Day (1914) and Herre (1924) who both recognized two endemic Puntius species in Lake Manguao. This study also confirmed the assumption made by Haig (1950) that the lake-endemic silurid catfish described by Herre in 1924 as Penesilurus palavanensis is just a junior synonym of Hito taytayensis, a silurid catfish whose distribution is only confined to Palawan. Results of the study revealed that the unique fish community of the lake still prevails 10 years after the introduction of O. niloticus. However, the fate of the native and endemic fishes in the near future should be a priority because most of the local fisherfolks claimed that the populations of some native and endemic species, some of which are listed as vulnerable under IUCN, have declined several years after O. niloticus was introduced.