Coastal fishponds require some essential equipment and facilities which are used for varied purposes. Such equipment may be used for maintenance and repairs, harvesting the crop, monitoring and maintaining water quality, excluding predators and pests, and other miscellaneous facilities for maximizing the use of various inputs.
Most of the maintenance and repair works in fish farms are devoted to dikes. Practically, the same implements in manual construction work are also being used in making repairs of dikes. Digging tools, flatboats, wooden dugouts and rafts as previously mentioned (Figures 6.4 to 6.8 in Chapter 6) are most appropriate for work like digging out trenches and backfilling them with puddled soil to repair leakage/seepage, and for deepening canals and other similar jobs.
Maintenance of digging tools are easily done by cleaning and rubbing with oil or grease to prevent them from rusting. Boats should be protected against the sun by putting them under the shed. Dugout boats, when not used, may also be filled with water to prevent the walls from cracking when exposed under the sun.
Practical and simple equipment have also been devised for levelling fishpond bottoms. The simple manual mud rake is a good example (Fig. 7.1), while in Indonesia, a levelling board manned by four or more men is also used (Fig. 7.2).
Fig. 7.1 A wooden mud rake
(After Rabanal, 1951)
|Fig. 7.2 Pond mud bottom levelling board used in Indonesia||Fig. 7.3 Fingerling seine (A) and operational view (B) (After Motoh, 1980)|
For manual removal of silt in fishpond bottoms or canals, a simple metallic or wooden shovel has been devised and used in Thailand and Indonesia (Fig. 6.5). If the area to be desilted is extensive, a type of silt or sludge pump can be used. This can be a small unit so that it can be portable and can be transferred to the various areas of the pond system.
The industry has designed various types of nets for use in fishpond operations. The fingerling seine, which is used for catching milkfish fingerlings and shrimps juveniles, is a fine-meshed rectangular net, about two to four meters long by one meter wide. It is supported by two poles at both ends with floats of wood, rubber or synthetic material on the upper side and sinkers of lead on the opposite side (Fig. 7.3).
A fingerling suspension net is usually a standard equipment in brackishwater fish farms. This is a rectangular or square net 2 to 3 meters wide by 3 to 5 meters long. Double line of coarse twine line the margins, the net has meshes of 0.5 to 1.0 cm square mesh. It is used to hold fingerlings during counting or before transport (Fig. 7.4).
This is a harvesting net of about 1.5 to 2.0 m wide by 30 to 50 m long (Fig. 7.5). It should have a float line at one of the long sides and lead line on the opposite side. It is made of coarse thread of nylon with mesh of 4 to 5 cm square mesh. To catch fish, this seine is dragged over the pond from one end to the other. The fish are gilled on the net but some jump over while small ones pass through the net meshes so that this net is usually used for partial harvesting.
Fig. 7.4 Sample of fingerling suspension net
Fig. 7.5 Part of a gill net for partial harvesting
Fine-meshed nylon or Manila hemp cloth are used as screens on frames on gates. These screens are usually framed with the wooden frame set on the gates to reinforce the bamboo screens on the frame (Figs. 7.6a and 7.6b).
For pipes, a fitting bamboo screen basket is used for milkfish nurseries in the Philippines (Fig. 7.7a). During the early stages of fry rearing, this is further coated with nylon mesh or Manila hemp cloth. Sometimes, only a fine-meshed net bag is tied to the water control pipe to screen-off unwanted organisms (Fig. 7.7b).
Fig. 7.6 Soil-sealed gates with screens
(After delos Santos, 1978)
Fig. 7.7 Netting screens in water gates and pipes
Bagnets so constructed so that their openings could fit the wooden frame for screens on gates are made for use in harvesting. These are installed on the frames during low tides when water is drained from the ponds which were previously fully flooded during the previous high tide. With the force of the current, the stock of shrimp from the ponds are led into the bagnet where they are collected. These harvesting bags for shrimp are used in the shrimp trapping ponds in Malaysia and in milkfish/shrimp polyculture ponds in the Philippines (Fig. 7.8).
Fig. 7.8 Harvesting net with lazy line-arrows indicate water flow
(After ASEAN National Coordinating Agency of the Philippines, 1978)
The net is a versatile net for fishermen as well as for fish farmers for small-scale individual catching or sampling. In fish farm, this net can be used for sampling stock of fish or shrimp to monitor growth or for partial harvesting when required (Fig. 7.9).
Bamboo screen traps have been devised for partial harvesting in coastal fishponds, especially for penaeid shrimps. In Indonesia, the shrimp fyke (bubu udang) is widely used (Fig. 7.10a). This consists of a fabricated catching fyke and an antechamber and a leader of bamboo screen set perpendicular to the pond dike. Series of the shrimp fykes may be set in the pond during harvest. In the Philippines, a similar trap is used but the catching end is formed in place rather than a pre-devised catching fyke (Fig. 7.10b).
Fig. 7.9 A cast net for sampling or partial harvest
Fig. 7.10 Traps for use in shrimp ponds
Portable water pump is usually used to effect water movement whenever needed in the pond system. This is often necessary when water circulation is needed and the tide condition is not conducive for this operation such as in alleviating stagnation or lack of oxygen.
Fig. 7.11 The Thai-made paddlewheel aerator towed
(After Menasveta and Leeviriyaphanda, 1982)
Paddle wheels set in the ponds can remedy critical oxygen condition. These devices can be powered by electricity or by small portable engines (Fig. 7.11). Better aeration of the pond water may also be accomplished through the gates with the use of the closure slabs (Fig. 7.12).
Fig. 7.12 Aeration by manipulation of closure slabs
(After delos Santos, 1978)
Water and soil analysis kits are now available in the market. For coastal fish farms a set that could monitor dissolved oxygen, salinity, pH, are most essential. Additional useful observations involve nutrient-content (N-P-K), depth of visibility (turbidity), etc. Simple visibility observations can be done using the Secchi disc (Fig. 7.13). Direct salinity readings using refractometers is easy to do but the equipment is quite expensive (Fig. 7.14). Improvised hydrometers may be used after standardizing them with a salinometer (hydrometer) or refractometer (Fig. 7.15).
Fig. 7.13 Measurement of depth of visibility by Secchi disc.
Fig. 7.14 Hydrometer and refractometer for measurement of salinity
Fig. 7.15 An improvised salinometer (After IFP, 1974)
Chilling chamber or box has become a standard facility in coastal fish farms. These are made of concrete, wood or galvanized iron sheets forming shallow tanks, square or rectangular in form scarcely 0.5 m deep set within the fishpond premises. It may be 2 to 3 m wide by 3 to 5 m long by 0.4 m deep. During harvest, this is filled with clean water and some crushed ice. The harvested fish or shrimp are placed in this box to wash and chill before packing them for the market (Fig. 7.16).
Fertilizer platforms (Fig. 7.17) where the sacks of inorganic fertilizers are placed so that the nutrient substances dissolve slowly into the water instead of chemically reacting with pond soil are useful facilities of the fish farm.
Fig. 7.16 Chilling tank for newly harvested milkfish
Fig. 7.17 Fertilizer platform (Source: Anonymous, 1976)
There are a number of devices designed to exclude predators and pests. The crab hook (Fig. 7.18a) is used to catch mangrove crabs that may have made burrows into the fishpond dike. Eel hooks (Fig. 7.18b) are used on moist pond bottoms to catch the mud eels that may persist to stay in the pond bottom after harvest. For predatory birds, various scaring devices are used. Lines of white twines are usually set over milkfish nurseries. Scarecrows may be set or other scares such as those using mirrors (Fig. 7.19), noise scares, moving scares, etc. A trap has also been devised for the mound-forming mud lobster, Thallasina anomala (Fig. 7.20).
Fig. 7.18 Devices used to get rid of pests
|Fig. 7.19 Bird scaring device (From Cook, 1977)||Fig. 7.20 Bamboo trap for mound-building mud lobster|