Appendix 2

SUMMARY OP THE REPORT ON EXPERIMENTAL CULTIVATION OF SHRIMP IN PDRY BY NICHIRO GYOGYO LTD. (MAY 1979)

Foreword

Basic surveys were carried out from August to October 1977. Full scale experimental research started in April 1978 on the cultivation of shrimp, baaed on a joint cooperative system between the Ministry of Fish Wealth and Nichiro Gyogyo Ltd.

Ultimate objective: industrialization of shrimp cultivation

1. Establishment of the Experimental Station

Site. Station set up in the building standing in the remains of the old fish factory on Labour Island, located in the back part of Aden.

Outline of Experimental Station. The building itself is approximately 43 m² , with round and square tanks. Need for a filter tank, as the seawater in the vicinity of the station was considerably polluted.

2. Summary of the Coastal Distribution of Shrimp in PDRY

Survey from August to October 1977, 1978 and 1979

3. Experimental Culture of Adenicus sp.

Carried out on a small number of individuals. For a good survival rate, (70 percent), it was necessary to carry out satisfactory water exchange, periodic replacement of sand bed, which had a great influence on the growth, daily removal of droppings, supplying of 02 by means of forced aeration, using an air pump, and carrying out continuous purification of breeding water. The very poor food efficiency means that the breeding was not done in good conditions and the growth curve gives a confirmation of some limiting factors.

4. Experimental Culture of P. semisulcatus

4.1 Distribution

All the fishing grounds were located west of Mukalla and up to Tabut (6th Gov.). The catches were made by one cuttlefish trawler, which was not especially designed for shrimp capture. Grounds: water depths were 10–30 m; water temperature surface 23–28° C, bottom 22–26 C; bottom composition soft mud, sandy mud. Fishing season and catch was from July to November, with the best catch from mid-October to mid-November.

4.2 Supply of Adults and Egg-carrying Shrimp

Supply of egg-carrying shrimp is very difficult even when Japanese trawlers working for cuttlefish are fishing. In case they catch egg-carrying shrimp, the eggs are released within 2 or 3 days following the capture. To attempt to secure egg-bearing shrimps for full scale culture operation, it will be necessary to operate a special shrimp boat centered around the fishing grounds at Sayhut, Fartak and Nishton to transport the egg-bearing shrimps back to the culture station immediately after catching (or to operate a special transportation vessel from ships to hatchery during the peak of catches).

4.3 Tank Rearing Tests of P. semisulcatus

No supply of egg-bearing shrimps. Production of fry by maturing shrimps in captivity and during reproduction. Capture by Nichiro trawlers regardless of eggs. During transport, shrimp were kept in a preserve tank of running water and fed 5–10 percent of B.W.

Conditions of rearing: WT = 24–28° C; salinities: more than 37.5 percent. Maturing and spawning is possible even with such high salinities and, consequently, along the coast of PDRY where there is very little fresh water flowing into the sea.

Maturing of adult shrimps. Three stages may be distinguished:

- initial stage: seen from the back, ovary is white and the ring portion is not clearly discernable; width of ovary, 5 mm;

- intermediate stage: colour changes to orange-white or green-white and ring portion becomes clearly visible;

- final stage: colour is dark green, width is 10 mm; shrimps must be transferred to the hatching tank at that stage.

Production of Juveniles

Hatching tank; square type made of polyvinyl sheets, 1.8 × 1.8 × 0.7 m. Water depth, 0.35 cm. Seawater used, filtered and fed through a plankton net. Aeration, air bubbles by mean of stones and blower.

Spawning was carried out during the night and hatching occurred approximately at noon of the following day, 36 h later. Plankton nets were used for inflow and outflow of the tank to prevent large plankton from coming in and shrimps from going out at the time of drainage.

Food for P. semisulcatus is the same as for other Penaus species. Diatoms: phytoplankton culture proved to be difficult in the coastal waters of the country. Diatoms which developed along the walls of the tanks were given as substitute food. No zooplankton supply problem near the station.

4.4 Problems in the Culture of Penaeus semisulcatus

The problem of supply of adult shrimps with eggs has not been solved, even with the help of trawlers. It is believed to remain a very difficult problem in the future.

Producing egg-bearing adult shrimps by means of tank rearing: what has been done is of great interest from a scientific point of view. From a commercial point of view, the long period of rearing prior to the spawning could be a major drawback. So, it is too early to extend this experiment on a large scale.

Feed. To produce juveniles, short-necked clams have been proved successful as in other experiments in Japan. However, recently, resources of short-necked clams were very low in the Aden area, and too small for the experiments. If any project were to be developed around the Aden area, it would be necessary to reserve a large area suitable for short-necked clam culture to secure sufficient feed for shrimp culture. It has been concluded that, although the possibility of carrying out shrimp culture with the P. semisulcatus in PDRY cannot be completely denied, it will first be necessary to carry out research in stock assessment in order to secure the supply and to establish a system of catching and transporting these shrimps. The foregoing process alone will involve a considerable period of time and substantial investments, with no guarantee of success.

HATCHING AND REARING PROCESS

T = 26–28°C during spawning; T = 24–28.5°C during hatching out and rearing.
Mortalities occurred when WT increased suddenly.
Salinities: over 37.5%

Report of the Visit to the Shrimp Station (7 April 1980)

At the time of Mr K.H. Mohamed's visit, data on shrimp cultivation were not recorded in the proper way. Since 1979. however, all tanks have been surveyed daily for water temperature, dissolved oxygen and salinity. These data are summarized in tables twice a month and allow good guidance of the cultivation. In case any of the above factors is changing, it can be corrected and the staff can keep a good balance by changing water/ sediment.

In April 1980, the shrimps in the tanks are all reproduced from the original shrimps brought from the 5th and 6th Governorates in 1978 by the trawlers of Nichiro Gyogyo. They represent the third generation of Penaeus semisulcatus alive in tanks.

Compared to the previous years, it may be said that problems are almost the same:

1. very limited facilities, shortage of breeding tanks and working space;

2. shortage of phytoplankton during the zoea and mysis stages;

3. limited quantities of short-necked clams for culture.

It is intended to solve the first problem by building a completely new station at Little Aden in a salt pan near the Persian pond (Fig. 1). This new station will work according to the same principles and a large culture pond (25 × 40 × 1 m) will be added to estimate the capacity of these pans as fattening ponds. The outline of this experimental project has been studied by Nichiro Gyogyo, which intends to support this experiment for the coming one or two years. Laboratory equipment is still rather short but it must be noticed that the whole experiment is supported by Nichiro.

To deal with phytoplankton shortage, it was suggested to try a simple technique of diatom collection under their own specific conditions. This technique is used in Japan for abalone during the first stage of culture and there is nothing new about it. It consists of collecting diatoms on corrugated plastic sheets immersed in seawater, hanged to a raft, two or three weeks prior to hatching. When the feeding starts at zoea stages, the sheets are removed according to the feed requirements and fixed diatoms are washed in rearing ponds.

No progress has been made in feed and trials using raw fish as feed for shrimps have produced comparatively poor results in growth. No doubt it will be necessary either to secure a steady supply of short-necked clams (or possibly oysters, which seem relatively abundant in Aden Bay, if there is no other way to use this resource), which seems very difficult, or to start production of artificial diets based on fish meal and other locally available ingredients.

Prospects of shrimp culture in PDRY

For production of juvenile as far as techniques are concerned, prospects are rather good. However, many problems are still unsolved, such as shrimp supply, etc.

Fattening from P.L. 20 stage to commercial size

- present experimental method is definitely experimental, not suitable for large scale culture;

- intensive culture in running water (Shigeno's method) is not adapted to local investment capacities and technological background;

- semi-intensive culture (Yamaguchi and Kumamoto type of culture) could be the only rational solution in PDRY.