The Government of Indonesia assisted by the United Nations Development Programme and the Food and Agriculture Organization of the United Nations have been engaged in a project whose main purpose is to:
develop suitable methods of intensive and semi-intensive culture of shrimps under local conditions;
introduce improved methods of milkfish culture, adapting them as necessary to local conditions, and develop new techniques for increasing the efficiency of operations;
develop suitable methods for mass rearing of shrimp larvae;
undertake surveys and studies to determine distribution and improve collection, handling and transport of milkfish larvae and shrimp fry;
organize studies on induction of maturation and spawning of milkfish and shrimps;
undertake in the vicinity of Jepara the demonstration of successful techniques of milkfish culture and training of field personnel, including extension workers in the application of such techniques, and
study the effects and extent of pollution and of pesticides and herbicides on shrimp and milkfish and to recommend suitable measures for controlling any adverse effects.
The project thus aims at improvement of the brackishwater fishpond industry of the country, which in 1972 extended over an area of about 165 000 ha of milkfish and shrimp ponds with an estimated additional 100 000 ha of mangrove swamps potentially convertible into such ponds. The main target is to raise milkfish production from the average 340 kg/ha/year to about 2 000 kg/ha/year and shrimp production from an average 200 kg/ha/year to about 1 000 kg/ha/year. This will result in an increase in the national income, providing additional employment and earnings of foreign exchange, in particular from shrimp exports.
As part of the project operation, FAO assigned Mr. Pedro G. Padlan as Fishery Biologist from 10 May 1974 to 31 May 1976 with the following terms of reference:
“Under the direction of the Project Manager, to organize and conduct experimental brackishwater fish culture leading to the development of improved techniques for commercial production, including:
developing intensive methods of nursery rearing of milkfish fry, ensuring least mortality and rapid growth up to fingerling stage;
evolving techniques of high production of commercial crops of milkfish;
developing poly-culture species combination for optimum production;
demonstrating improved techniques for training and extension.”
The majority of the brackish water fishponds of Jepara are located and distributed as follows: (Source, Fishery Office, Jepara, 1974)
| Location | Area (hectares) | |
| Jepara town | 170.15 | |
| Keling | 235.80 | |
| Kedung | 337.12 | |
| Others | 38.91 | |
| TOTAL | 781.98 | |
The figure for Jepara includes the 50 ha of the Shrimp Culture Research Centre experimental ponds.
The soil of the fishponds in Jepara town is alluvial, predominantly reddish clay, brought down from the hills bordering nearby. Those very near the coast are sandy, of coral origin. Samples of soil from two ponds of the experiment farm analysed by the Soil Research Institute, Bogor, in 1974 showed the following values:
| Pond No. | Sample No. | Texture (%) | CN Ratio | P2O5 | K2O | Ca ppm | Mg ppm | Fe ppm | SO4 ppm | |||||
| Sand | Silt | Clay | pH | C(%) | N(%) | (mg per 100 gm) | ||||||||
| E-2 | 1 | 1 | 24 | 75 | 7.8 | 3.22 | 0.18 | 18 | 101 | 251 | 5 643 | 6 891 | 547 | 9 271 |
| 2 | 1 | 24 | 75 | 7.7 | 3.29 | 0.17 | 19 | 114 | 257 | 5 823 | 7 006 | 546 | 9 451 | |
| E-4 | 1 | 5 | 27 | 68 | 7.6 | 3.02 | 0.19 | 16 | 113 | 252 | 9 528 | 8 380 | 780 | 10 880 |
| 2 | 5 | 26 | 69 | 7.6 | 4.16 | 0.18 | 23 | 124 | 255 | 4 398 | 8 194 | 900 | 10 890 | |
There are two distinct seasons in Jepara, a dry period starting from May and lasting up to the early part of October, and a wet season during the rest of the year. Rains often come in downpours with heavy precipitation within a short time. From records of the local Agricultural Office, the average rainfall and number of rain days per month during the ten year period 1961–70 were compiled and are shown in Table 2.
| Month | Rainfall (mm) | No. of rain days | Month | Rainfall (mm) | No. of rain days |
| January | 830.1 | 24 | July | 25.8 | 1.8 |
| February | 596.3 | 21.5 | August | 7.7 | 0.9 |
| March | 332.8 | 17.5 | September | 19.7 | 1.1 |
| April | 147.8 | 11.3 | October | 43.8 | 3.5 |
| May | 50.7 | 5.4 | November | 165.0 | 8.5 |
| June | 52.7 | 3.5 | December | 396.1 | 19.9 |
| Total yearly avarage rainfall = 2 688.4 mm | |||||
| Average number of rain days/year = 118.6 | |||||
Daily records of atmospheric temperature compiled by the Fish Culture Section from November 1974 to October 1975, showed the following readings:
| Month | Day temperatures (°C) | Night temperatures (°C) | ||
| Range of highest temperatures | Mean | Range of
lowest temperatures | Mean | |
| November 1974 | 32.5 – 33.5 | 33.0 | 25.5 – 27.2 | 26.6 |
| December | 28.7 – 36.0 | 32.1 | 25.8 – 28.0 | 26.6 |
| January 1975 | 28.0 – 34.5 | 31.5 | 25.0 – 28.0 | 26.6 |
| February | 27.5 – 33.5 | 30.1 | 25.0 – 28.5 | 26.2 |
| March | 29.0 – 33.0 | 31.2 | 25.4 – 27.5 | 26.8 |
| April | 29.8 – 33.0 | 31.1 | 25.5 – 28.0 | 26.3 |
| May | 28.5 – 33.0 | 31.4 | 26.0 – 27.5 | 26.5 |
| June | 30.0 – 32.5 | 31.7 | 26.0 – 27.5 | 26.6 |
| July | 30.0 – 33.0 | 32.0 | 26.0 – 29.9 | 27.1 |
| August | 31.5 – 34.5 | 32.1 | 26.3 – 27.5 | 26.8 |
| September | 30.5 – 35.5 | 33.0 | 26.5 – 27.0 | 26.8 |
| October | 32.7 – 34.1 | 33.5 | 25.5 – 27.7 | 26.6 |
The fishponds of Jepara get their sea water supply from the Java Sea. Tidal predictions given in tide tables issued in 1974 for the nearest reference point, Semarang, show the highest astronomical tide as 0.9 m and the lowest as 0 m. The Port Authority at Jepara has established a bench mark near the mouth of Wiso River, less than a kilometre from the ponds of the centre and the highest tide actually recorded by them during 1974 was 0.93 in January and the lowest, -0.2 m in April.
During 1972, 25 000 ha of brackishwater fishponds in Central Java produced 3 311 t of fish (Fishery Statistics of Indonesia, 1973) averaging 132.5 kg/ha. In the same year, fish production from the brackishwater ponds of Jepara totalled 175.8 metric tons. In 1973, production rose to 271.3 t and in 1974, dropped to 196.6 t (Jepara Fishery Office records). On this three year basis, average production of the three major crops amounted to:
| Milkfish | 71.07 kg/ha/yr |
| Shrimps | 143.12 " |
| Miscellaneous species | 65.04 " |
The figure for milkfish is surprisingly low at first glance. This, however is, easily explained by the fact that the Kedung section which has the widest acreage is not systematically stocked with milkfish and produces only shrimps and miscellaneous fish species which come into the ponds as seedlings through the inlets. Considering only the Jepara town and Keling areas as the major source of brackishwater pond milkfish, it may be safe to assume that the average milkfish production of these two areas for the same period is somewhere around 137 kg/ha/yr.
The traditional method of raising milkfish in ponds in Java was described by Schuster about 25 years ago. This is still practiced in Jepara. Milkfish fry are planted directly in a small nursery located inside the production pond. The “baby box”, as it is often referred to is constructed with small dikes and consists of two compartments - a small area of about 4 m2 adjoining a bigger one of about 30 or more square metres. The fry are stocked in the smaller area where they stay for a few days before they are allowed to the next larger compartment by simply breaking the common dike. The late fry are released to the production pond after two or three weeks also by cutting the dikes.
Fertilizers are very rarely, if at all, applied. The ponds are harvested totally when the fish reach marketable size of about 200 g and above. Two crops per year are produced, depending upon availability of fry. Recovery of marketable fish is more often below 50 percent.
Twenty-one ponds with an aggregate area of approximately 20 ha were initially allocated for experiments and studies by the Centre. These were partially remodelled, resulting in the formation of 10 nursery ponds ranging from 400 to 800 m2, 8 fingerling ponds of about 2 000 m2 each and 16 rearing ponds of from 5 000 to 14 000 m2.
Development of this area was far from complete. No ponds could be fully drained. Some would be dry at the centre, with water only in the peripheral canals during neap tide periods. Others had been constantly under water. Dikes are wide. However, they had not been compacted properly, nor had puddle trenches been dug to bind them with the ground. Consequently, leaks are numerous and seepage is very difficult to control. Also, considerable water is lost through the sluices and unless these are blocked with soil after every water intake, decrease in depth of up to five cm between two successive high tides is not infrequent.
Compounding the problems was the state of the main canal. This water channel is about two km long and from 10 to 12 m wide. It supplies tidal waters and is the main drainage venue for almost 80 ha of fishponds in the area. Siltation had raised its bed and constricted it at several points, reducing water flow and rendering some shallow ponds undrainable. Sand bars form very readily near the mouth during the NW monsoon. The ponds are also some distance from the Research Centre. Many times, this has given problems of security of the fish stock.
A remedy to all these was the acquisition of all the ponds extending towards the Centre and their consolidation into an integrated unit. This increased the total area of the Centre's experimental farm to about 55 ha. As a result, the main canal was appropriate solely for use of the Centre. A 6-door main concrete sluice was constructed at its mouth with fittings for a 20-inch low lift pump powered by a 55 Hp Diesel engine. Renovation and remodeling which started in July 1975 included deepening of this canal, installation of 1- to 3- door concrete sluices for the lateral canals, excavation and levelling of ponds to enable them to hold from 40 to 120 cm of water and fitting them with standard wooden sluices.
Although the work is still incomplete and the condition of the ponds is far from satisfactory, some of these were commissioned for experimental studies and testing of improved techniques of milkfish rearing and production. Meanwhile at the Centre, small scale preliminary experiments were conducted in plastic limed pools, plastic tubs, etc. on various aspects of environmental monitoring, fertilizer response and pest control as basis for future large scale trials in ponds.
