It is quite probable that enough freshwater will be available only in the rainy season. When the water supply becomes short during the dry season, the water from the first phase ponds can be pumped into the others. The necessary water level and the fish culture have to be maintained in at least half of the ponds during the dry season because wastewater will be produced continuously and has to be distributed daily. If the hydrological investigation shows that enough surface water can be collected from the airport terrain during the rainy season, an additional simple reservoir may help to keep the fish-pond filled. It could be observed that there was quite a run-off of water from the hilly area south of Batu Maung (Fig. 9.2) being collected in a canal. This should be conveyed to the pig estate area to fill the ponds and additional reservoirs. A place for such an additional reservoir pond with 200 to 400 m3 capacity might be the Lot No. 400 (Fig. 9.2), which has to be connected with one end of the open dam crown canal through a ca. 900 m pipeline. A cost estimation for this water supply is given in ANNEX I.
If further calculations will show that the water supply is insufficient during part of the year, brackishwater fish culture must be used. The necessary seawater must be pumped from suitable place through a closed pipeline to the distribution canal on the dam crown. Care must be taken that the sea-water intake is as distant as possible from the adjacent estuary of Khong river discharging effluents from the nearby industrial estate into the Strait of Penang (Fig. 8.2).
Schroeder (1979) describes that the manure-loaded fishpond can be considered as a system to which mineral-rich organic matter is added in the form of manure and removed in the form of harvested fish. In this sense, in a properly managed pond, there will be an ecological balance that avoids the extreme biological cycles so commonly observed in highly eutrophic water bodies.
The addition of manure to a pond provides a nutrient base for dense blooms of phytoplankton. This in turn results in intense zooplankton growth which feed upon the nanoplankton. The zooplankton have an additional food source in the bacteria which thrive upon the added organic fraction of the manure. Without predation upon this zooplankton community, its growth, based on the dual food chain, soon exceeds the corresponding production of phytoplankton. The zooplankton overgraze the phytoplankton; photosynthetic oxygen production becomes inadequate to supply the respiration demands of the total pond community (bacteria, protozoa, zoo- and phytoplankton). The pond becomes anaerobic; the zooplankton population dies, gradually decays and a new cycle of phytoplankton growth starts. It has been clearly demonstrated (Schroeder, 1975; Allen and Carpenter, 1977) that ponds receiving high loadings of manure or other nutrient rich organic matter, when stocked with a proper polyculture of fish, do not have these extreme cycles. The fish grazing on the plankton community maintain the balance between plankton production and consumption. The pond remains aerobic with higher average dissolved oxygen (DO), higher pH and lower standing stocks of phytoplankton, zooplankton, benthic chironomid larvae, and pelagic bacteria.
The critical question in fish culture is how much pig waste can be utilized as fertilizer per unit area of fishpond without endangering the oxygen balance of the pond - that is, without running the risk of fish kill from oxygen depletion.
Practice has shown that the quantity of pig, or other animal waste utilizable in fishponds without risk to fish life depends on the waste delivery and distribution methods employed. For example in Hungary, where the fish growing season is only 150–180 days per year, it was possible to distribute 300–600 kg manure over one hectare pond surface per day. One fattening pig produces on the average 6.7 to 7.5 kg of manure (Table 10.2). This means the total manure output of 40–90 pigs or the liquid phase from 130–300 pigs can be distributed per day. This is based on the information in Table 10.2 that the amount of dry matter in the liquid phase contains only one-third of that in solid waste.
The maximum possible waste loading in fishponds has not yet been determined experimentally. Theoretical calculations can show that the quantity of waste that can be processed per unit area of fishpond, without the risk of oxygen deficiency, can be two to three times more than the quantities indicated above. In fact, this manure rate can be much higher as applicated by Schroeder, 1978. According to his figures, up to 140 kg dry organic matter were applied per hectare per day. Taking again above figures, this relates to the daily waste of 1 700–1 900 pigs, an indeed high figure. There is, however, no doubt that the liquid waste phase of ca. 1 000 pigs could be treated and utilized in one hectare pond area. This means for Batu Maung, with a standing pig population of 11 000, that ca. 10 hectare pond surface are necessary for the waste treatment. The distribution of the liquid in the ponds should be as even as possible. The already mentioned sprinklers achieve this best and secure additional oxygenation of the water. The application of the waste must only be done during the morning hours, ca. 8.00 to 12.00 h. It has been found that with later application, the photosynthetic oxygen production stimulated through each fertilization process is not high enough to ensure a sufficient oxygen level during night time.
As with animal husbandry in general, in fish farming, poor yields are the result, usually, of poor management. There may be unforeseen losses resulting from a prolonged period of low solar radiation (unseasonably cloudy weather) and hence low photosynthetic production of oxygen, anoxia and fish kill; however, proper management must consider the general climatic conditions as well as the pond environment.
The low fish yields discussed in the previous section result primarily from two deficiencies: improper fish stocking, and improper use of manure. Monoculture, unless it is a fish that has a readily adaptable feeding pattern (as is reported by Odum, 1970 for the milkfish Chanos chanos), will result in inefficient utilization of the natural food. Polyculture requires species that will harvest different parts of the food web (see Table on page 15). Adequate density is also required. Up to the carrying capacity of a pond, fish yield will increase with increasing fish density. Exceeding the carrying capacity results in more of the available energy going for fish maintenance, and will result in decreased total yield.
Inadequate amounts of manure fail to supply the required substrate for microbial growth. Piling large amounts of manure in the pond produces aerobic digestion and high microbial activity only at the surface of the pile. A few millimeters within the pile anaerobic conditions result in inefficient conversion of substrate carbon into microbial cells, low microbial activity, and production of three toxic agents: Hydrogen sulfide, ammonia and methane.
If the soil in which the pond is constructed is excessively acid, or if the supplied water is very soft, there will be poor microbial development, poor digestion of the manure, and hence, low autotrophic-photosynthetic and heterotrophic productivity. Without the basic yield of these natural foods, fish yields will be correspondingly low.
There is no doubt that to this date, the silver carp and, to a much lesser extent, the bighead carp, are the best suited cultivated fishes for the utilization of phytoplankton bloom resulting from waste enrichment. These fish species have a fine filtering apparatus which strains algae of 20 microns or more in the course of normal respiration. In warm water (above 22°C), the respiration rate is faster and a greater quantity of plankton is filtered per unit time. Sarotherodon (syn. Tilapia) galileus and other cichlids cannot match these carps, Woynarovich (1979).
The composition of the fish stock will depend on several factors: (i) the desired size of the fish at harvest; (ii) the initial weight of stocked fish; (iii) the length of the growing season; (iv) the average water temperature; and (v) the fish carrying capacity of the pond (quality of the pond).
In Hungary, to raise advanced fingerlings of 20–30 g each, 60 000 early fingerlings of common and Chinese carps1 are stocked achieving a yield of 15–18 tons/ha/year. Stocking at an adequate number is essential, as well as the right polyculture, or at least a fish species with diverse feed selection, is essential. Harvesting of pelagic and benthic niches gives more complete food utilization.
The following table shows the normal feeding habits of some fish species (Schroeder, 1979):
| Species | Phytoplankton | Zooplankton | Detritus | Filamentous algae | Macrophytes | Benthic organisms |
| Silver carp | **** | **** | ||||
| Bighead carp | **** | |||||
| Common carp | **** | **** | ||||
| Grass carp | **** | |||||
| Mud carp | **** | |||||
| Milkfish | **** | **** | **** | **** | ||
| Tilapia nilotica | **** | **** | **** | |||
| Tilapia aurea | **** | |||||
| Grey mullet | **** | **** |
1 Species of bighead, silver, grass and other carps common in China are used in culture.
Piggery waste utilization in fishponds, provided the optimum conditions are met, cannot be but economically profitable. In common carp monoculture, a yield increase of 2.5–3 kg can be obtained from 100 kg manure or the respective liquid of ca. 400 kg total waste (Woynarovich, 1979).
In well-designed mixed culture, with common carp as the main fish, a yield increment of 3.5 to 4 kg can be realized with the same amount of manure. If silver carp is the main fish and common carp is only a secondary fish, a yield increase of 6 kg can be expected from 100 kg manure.
For example, in Hungary, one large fish farm (254 hectare pond surface area) which utilizes pig wastes regularly produces an average of 2 to 2.3 tons of fish per hectare per year. The gross income of this farm is US$675 000 with a profit margin of US$165 000. One person in the farm is producing fish, valued at ca. US$25 000 of which ca. US$6 000 is profit.
In this farm, 21 tons of pig manure is distributed daily in the ponds. This corresponds to the daily manure output of 2 000 pigs. It is evident also that the farm could utilize manure of more pigs in these ponds, especially if only the liquid waste phase would be applied. In the tropics and subtropics, where biological processes are faster due to the higher temperature, more pig manure can be utilized in the fishpond provided that 5 000 to 7 000 or more fish (20–30 g each) made up mainly of filter feeding fish species are stocked per hectare.
One quite important factor is, of course, the sale of fish raised in ponds fertilized with pig manure. In a sensitive area with a population of different ethnic groups and religions, this might become a problem. The marketability of a high pig production, however, does not seem to be a problem. Therefore, it might be advisable from the economical point of view to raise a fish species that is again converted and added to the pig feed. The quality of such a feed is obvious and it would reduce feed costs considerably.
Although the State of Penang, in the Department of Agriculture, has funds available for rural development in the western part of the Island of Penang, it is recommended that a pilot project for wastewater management be started in Batu Maung in the eastern part where the constraints are more typical of what is happening today to animal production throughout the world. Funds for west Penang should be made available to develop a pilot project in Batu Maung which would likewise be profitable for Pantai Acheh.
