This part of the report contains the specific engineering designs based on the findings in the field and requirements of Shilat as detailed in Part I. It consist of the basic considerations used for the design, basic assumptions used, description of the various facilities, specifications, and technical drawings. As much as possible sufficient information has been included to enable Shilat engineers to prepare the detailed engineering design. Many of the designs, especially those pertaining to the hatchery in Mahshahr, has previously been presented and thoroughly discussed in a series of technical meetings in Tehran between the Consultants and Shilat staff.
Specifically the designs and description of the following facilities are included in this report:
Hatchery System
Indicative design of a model 100 million PL capacity shrimp hatchery not specific to any location.
Indicative plans for converting the warehouse in Mahshahr, Khuzistan province, into a 100 million PL hatchery.
Indicative plans for converting the old cold storage plant in Jask, Hormuzgan province into a shrimp hatchery.
Indicative design of seawater purification system including designs of specialized components such as sedimentation tank and rapid sand filter.
Indicative designs of larval rearing tanks, nursery tanks, algal culture tanks and broodstock tanks.
Indicative designs of various types of seawater intake.
Layout of algal culture laboratory.
Pond System
General layout of 1,000 ha shrimp farm estate in the Helleh River Area, Bushehr and subdivision into 5 ha and 25 ha shrimp farm modules.
Model layouts for 5 ha and 25 ha modules.
Indicative design of pump installation including system of mixing fresh and salt water.
Typical sections of canals and dikes.
Indicative designs of pond inlet structure.
Indicative designs of drainage gate.
The basic task given to the Consultants by the Shilat Aquaculture Department was to design a hatchery capable of producing 100 million postlarvae per year. The additional task was to determine whether an existing warehouse in the Shilat fishing port complex in Mahshahr, Khuzistan, could be converted to such a hatchery, and to prepare a practical plan for such a conversion if found suitable. If the said warehouse is found not big enough or completely not suitable, an alternative site was to be identified for either a supplemental hatchery of such as a size as to make up for its deficiency or an entire 100 million capacity hatchery as the case may be. A practical plan for converting an old cold storage plant in Jask, Hormuzgan province, into another hatchery. Meanwhile another unused warehouse inside the Shilat compound in Bandar Abbas was merely to be examined for its suitability for conversion into a hatchery.
The question of shrimp species to be reared is not an important consideration in the design of a hatchery. There is no compelling evidence to suggest otherwise. Indeed as has been the experience in Kollahi, the same facilities worked equally well for the three species tried. Differences in the treatment of each species will likely come in during hatchery operation such as, for instance, in terms of providing an optimum salinity level. The hatchery designs presented in this report include the provision of a freshwater line for such requirement.
Before making any production assumption it was necessary to first define what “one year” means in the context of hatchery operation in Iran. To do this required looking at the entire shrimp culture process backwards, starting from the harvest of marketable shrimps from the grow-out ponds.
Based on the monthly temperature trend, it was determined that the grow-out ponds have to be harvested by late autumn. For calculation purposes it was assumed that all the ponds have to be harvested by mid-November. Allowing for a 4 month growing period, this means mid-July as the last possible date for stocking, which is also equivalent to the last possible date for producing shrimp fry. The spawning season is known to occur during spring which officially starts with the vernal equinox, March 21. For calculation purposes, it is assumed that spawners will start to be available by the first of April, which then determines the hatchery's initial operation period. Thus for this study, one hatchery year in Iran is defined to be 105 days.
There is no standard or set stage for stocking shrimp fry in grow-out ponds. The usual stage for releasing them in ponds can range from PL-10 to PL-30. For the purpose of this study i is assumed that the shrimp fry shall be stocked at PL-20 stage. This is a practical stage since it requires about one month from spawning for the shrimp to reach this stage. In many hatcheries, the production of PL-20 fry is done as a single or one-step process. If this is followed then within the 105 day hatchery operation period, only 3 turnovers can be realized per year. However by adopting a two step process where the larvae are reared up to PL-5 in larval rearing tanks and then transfering them to nursery tanks for an additional 15 days of rearing it is possible to realize 6 turnovers.
The two-step process offers other advantages. Generally the shrimps are more sensitive and requires better care during the larval stages than during the postlarval or juvenile stages. Thus while it is necessary to rear the larvae indoors, where a more stable temperature can be maintained, using treated and possibly heated water, the rearing of the postlarvae can be done in an outdoor tank using only filtered water. Another advantage is that transferring them to another tank means new and clean water free from wastes which accumulate after 2 weeks even with regular water change. The final design therefore took this into account and provided for separate larval rearing tanks and nursery tanks.
With only 6 production cycles possible in one year, the proposed hatchery has to be large enough to produce 16.7 million PL-20 every 17 days in order to produce 100 million PL-20 annually. This is the starting point for computing the number of culture tanks as shown in Annex 1. To produce 16.7 PL-20's, the number of PL-5's required was computed by assuming a 70 percent survival rate, while a 35 percent survival rate was assumed from nauplii to PL-5. (It should be noted that even during the first culture trial in Kollahi in 1992 a survival rates of 40 percent from nauplii to PL-6 and 55 percent from PL-6 to PL-26 were attained using P. semisulcatus inspite of the limitations imposed by the poor site and facilities.)
The total culture tank volumetric requirement for larval and postlarval rearing were computed by setting the initial density at 80 nauplii per liter and 25 PL-5 per liter respectively. These figures are not arbitrarily selected but are based on usual practice in existing hatcheries. Finally the number of culture tanks required was computed by setting 12 m3 as the standard larval rearing tank size and 24 m3 for the nursery. These tank sizes were selected for practical reasons. A 12 m3 tank can be operated even with only 6 spawners. The tanks can be constructed in pairs sharing one common wall, resulting in some savings in cost, but still capable of being easily cleaned even if one side (the partition wall between 2 tanks) is not accessible. Furthermore the initial stock per tank is close to 1 million nauplii. With the assumed initial densities and survival rates, the 24 m3 size of each nursery tank is just large enough to receive the PL-5 output produced by a pair of larval rearing tanks.
A ready supply of micro-algae is an important factor for successful larval rearing. The maximum feeding level in the larval rearing tanks was set at 100,000 cells per ml while the maximum culture density was assumed to be 800,000 cells per ml. With these assumptions it was calculated that a total algal culture volume equivalent to 12 percent of the larval tank volume will be sufficient to supply enough micro-algae. In order to facilitate the culture process, an elevated starter tank has been incorporated in the design of each mass culture tank. The algal mass culture tanks are designed to be indoor as one part of the hatchery. This was done due to the experience in Kollahi during the trial culture in 1992 during which the frequency and quantity of wind-borne dust was found o be constantly affecting the quality of culture in outdoor algal tanks.
Broodstock tanks have been incorporated in the design for two reasons. One is the expressed desire of Shilat to propagate an imported species, P. monodon. Two, the observation that the number of gravid females of the locally available species dwindles towards late spring. With maturation facilities it becomes possible to include even non-gravid adult female shrimps in the collection. Due to the lack of basic data on reproductive capacity of captive broodstock under Persian Gulf situation, certain assumptions had to be made. These assumptions include a male to female ratio of 1:3, a maturation success rate of 80 percent, and a nauplii production of 100,000 per spawner for P. semisulcatus and 150,000 per spawner for P. monodon. It is further assumed that for the locally occurring species part of the spawner requirement will be filled by naturally gravid females.
The layout of hatchery took into consideration the fry production process, direction of seawater supply, access, and drainage, among others. Service areas consisting of work counters with sinks at strategic points are also incorporated in the layout. Adequate space is also given for the personal needs of the hatchery staff.
The type of seawater intake system depends on the beach profile, type of substrate, exposure to wave action and tidal range. In areas with sandy substrate, either inshore or offshore wells can be employed. In such case the water is pre-filtered and a rapid sand filter is no longer necessary. In an area with muddy substrate, only an open type of intake is possible and a sedimentation tank and rapid sand filter are required to make the water suitable for larval rearing.
For either type of site and intake system, a means to treat the water before usage is necessary in order to minimize the risk of disease. Although there are many ways or devices for purifying water such as ozonation and ultraviolet treatment, batch chlorination was selected for the simple reason that it does not require any special machinery or equipment and therefore is not subject to breakdown; is known to be effective; and is in use in many commercial hatcheries. In order to make the temperature of the treated water as close as possible to that of the larval rearing tanks, the treatment tanks are enclosed (roofed and walled). Two sets of treatment tanks are provided. One for larval rearing and another for algal culture which requires a stronger chlorination level (30 ppm calcium hypochlorite as against 15 ppm).
The design of the water distribution system took into consideration the different needs of the various units of the hatcheries. For the larval rearing tanks, the seawater available by default comes from the treatment tank for 15 ppm Calcium hypochlorite; for algal culture, seawater treated with 30 ppm calcium hypochlorite; and for the nursery tanks, filtered water. All the three seawater source will be provided with a header tank in order to maintain constant pressure.
Due to its size, the hatchery is subdivided into sectors with each sector provided with separate operating and back-up blowers. The nursery will consist of 2 sectors, the larval rearing area another 2 sectors, the algal culture and broodstock tanks, separate sectors by themselves. The algal culture laboratory where stock and starter cultures shall be maintained is provided with its own internal blower. The advantage of such a system is that pressure drop due to distance from the blower shall be greatly minimized, inter-tank contamination limited to each sector, and hatchery-wide air interruption due to equipment breakdown not likely to occur. All aeration pipe shall be installed overhead to prevent siphoning of water into the aeration hose in case of momentary power interruption.
The stand-by generator, the water pumps and the blowers will need to be provided with their own houses to protect the machineries from the elements. For a large hatchery a laboratory for maintaining stock cultures and pure cultures of different species of micro-algae is necessary to ensure a ready supply of quality starter stock. A storage area is also required for keeping spare equipment and stock of consumable. Finally a hatchery will need a place for the technicians and the workers to stay so as to be available anytime required during the hatchery season; and an office for conducting administrative routines.
The warehouse in Mahshahr was found big enough to be converted to a 100 million PL's per year hatchery as shown in Annex 2. The proposed hatchery will make use of the central enclosed area of the existing shilat warehouse for the larval rearing tanks, the algal culture tanks and the broodstock tanks. The nursery tanks will be positioned within the side extensions which are roofed but not enclosed. The water treatment and storage area will be housed in a separate structure. Due to the high sediment load in the water, a large sedimentation tank is provided. The sedimentation tank also serves as the main reservoir. With a capacity of 900 m3, it is designed to hold enough water for one day's requirement at full operation. Such a large reservoir is necessary because it is safe to pump seawater only when the tide is high. When the tide is low there is an increased risk of taking in the occasional oil slick and garbage from the fishing boats.
From the sedimentation tank the seawater will be pumped up to a rapid sand filter from which the filtered water flows down to the filtered water reservoir (capacity of 600 m3). From the filtered water reservoir, the water can either be pumped up to a header for distribution or be made to flow by gravity to the either of the two treatment tanks (capacity of 300 m3 each) which are set slightly lower. Because it requires 24 to 36 hours for the water to be ready for use, two treatment tanks are provided so one will always have treated water ready for use while the other is still under treatment. In the treatment tanks salinity adjustment, EDTA treatment, chlorination and dechlorination under constant aeration are undertaken. After the requisite treatment time, the treated water is pumped up to another header for distribution -- mainly to the larval rearing tank. A separate pair of treatment tanks is provided for algal culture due to higher chlorine concentration requirement.
In order to maintain a good larval rearing temperature (28 to 30° C), the treatment tanks will need to be provided with heaters. The enclosure (roof and walls) will help prevent temperature fluctuation. Either electrical immersion heaters or a heat exchanger system using steam from a boiler can be used provided the heat exchange pipe is made of stainless steel. Inside the larval tanks the rearing temperature will be maintained by using plastic tank covers. Provision should also be made for electrical immersion heaters which can be moved from one tank to another when necessary for maintaining the rearing water temperature.
The proposed conversion of the old Shilat cold storage plant in Jask assumes that the entire building will be used. With an internal floor space of only 1,960 m2, it was calculated that the resulting hatchery will have a capacity of only 41 million PL-20, as shown in Annex 3. Due to space limitations, it was found necessary to design the nursery with 3 different tank sizes, 32, 24 and 21 m3. A uniform size of 12 m3 was however maintained in the larval rearing tank design.
The seawater supply system in Jask is very much simpler due to the availability of pre-filtered seawater from inshore wells. Therefore there is no need for a sedimentation tank and a rapid sand filter. Seawater from the well is simply pumped up directly to a header. There is also no need for a reservoir since clean seawater can be pumped anytime regardless of tidal level. Treatment tanks are still provided however for chlorinating the water supply.
In the layout the algal culture area has been set in the side extension using circular 5 tonner fiberglass tanks. Lighting will come from natural sunlight. This is a more conventional manner for algal rearing. This can be done at Jask because it appears that due to its location in a promontory jutting out into the Sea of Oman, the air is generally clean and dust free.
In designing the maturation facilities, it was assumed that only local shrimp species such as P. semisulcatus shall be used in the Jask hatcheries. It was further assumed that the indoor broodstock will produce only 50 percent of the total nauplii requirement with the other 50 percent coming from wild gravid females.
Due to the pronounced climatic season in Iran, the onset of winter will set a natural limit on the growing period. This will most likely vary slightly depending on the location along the coast. Towards the north, from Buhsher to Khuzistan, it is likely that the temperature will be warm enough for pond stocking only by the middle of May. As mentioned earlier, it is also likely that the pond water temperature will already be too cold for further rearing by the middle of November. From mid-May to mid-November is only 6 months. One growing cycle will need 4 months. Thus from Buhsher northwards, only one crop a year would most likely be possible.
Towards the south, from Hormuzgan to Seistan-Baluchistan, it is likely that by early May, pond stocking is already possible and that the growing period can be extended all the way to December for a total period of 8 months. Counting the preparation period in between crops, 8 months is still a little short for 2 growing cycles. However the possibility of a shorter fall crop should still be explored. And as has been discussed earlier the possible use of M. affinis as a second crop should be explored.
Iran has a vast area of saline flats ranging from intertidal to low supratidal in elevation. Granting that an area has acceptable soil and good water source, it would still not be advisable to develop an area indiscriminately without regard for its elevation relative to tidal datum. In the lower intertidal zone which is always watered everyday, the ground will be too waterlogged and will not be able to support heavy equipment for earthmoving. Therefore it would be more practical to limit development to the upper intertidal and lower supratidal zone. The acceptable elevation will depend on the tidal regime in a locality. In the Bushehr area where the tidal range is only 2.4 m, the optimum elevation will be from 2.0 m up. In the Hormuzgan area where the tidal range in 4.2 m, the optimum elevation will probably be from 3.8 m up.
Shrimp culture varies from low density extensive system capable of harvesting only 100 to 200 kg per ha per crop to hyper intensive system capable of producing more than 10,000 kg per ha per crop. While it is always tempting to push the limits and aim for the highest production possible, it may not be appropriate nor would it necessarily be more profitable. In an area where there is an abundance of idle land like Iran, there is no compelling reason to adopt intensive culture technology with its attendant risks. Taiwan had to go intensive having no choice due to the limited land resource. Definitely however, due to the high cost of development, it will not be profitable to go extensive. The best alternative therefore will be to adopt semi-intensive system.
There is no clear cut boundary in the stocking density between intensive and semi-intensive system. Generally however a farm can be considered semi-intensive if it is capable of being managed without using aeration devices. A semi-intensive pond will still require a good water supply regardless of tidal condition -- which means the use of pumps. This is then one of the basic considerations in the design of the ponds in this report.
In designing the water distribution system, it was assumed that all of the water requirement will be supplied by pumping and that on the average 10 percent daily since freshwater or brackish water is available for salinity management in the site being considered in this report.
Since a semi-intensive system is to be employed, the basic pond size has been set at 1 ha. There are two reasons for this selecting this size. One, in constructing the pond only 50 cm will need to be excavated to produce enough soil for diking. Construction of smaller size ponds require more soil for dikes and therefore deeper excavation. Deeper excavation may lead to hitting the water table and produce problems in draining and drying the pond. Two, 1 ha is a practical size for feeding, water management and harvesting. A larger pond will be difficult to manage and harvest.
The soil type determines the size and slope of dikes and canals. Although soil problem can be avoided through a more careful site selection, sometimes an area with poor soil characteristics is still used due to other factors, such as for instance the availability of freshwater or low salinity water for salinity management. One important consideration is the capability of the soil to retain water. The dikes and canals therefore should be designed according to the soil type.
The specific instruction of Shilat Aquaculture Department management was to subdivide the farm estate area into small and medium size farms measuring 4 ha and 20 ha respectively. Of the total area 60 percent is to be allocated for the 20 ha farm units and the remaining 40 percent for the 4 ha farm units. Later, after a preliminary design by the consultants, it was determined that it would be more practical and efficient to use 5 ha and 25 ha sizes. This was agreed upon by Shilat management.
In subdividing the area the primary consideration was to have an efficient water distribution and drainage system with no possibility of conflict between individual operators over the saltwater supply. The layout also allows each individual farm operator to change water independently of each other and of the central estate management.
Basically the entire 1,000 ha area was first subdivided into blocks of 50 ha size with each block served by a secondary supply canal and a secondary drainage canal. Each block was then subdivided further into 5 ha and 25 ha farm units. The actual size of each farm unit including dikes and canals are 8 and 38 ha respectively. With such a layout it was determined that the net watered area constitutes approximately 65 percent of the total. The layout resulted in a total of 49 units of 5 ha farms, 13 units of 25 ha farms and one unit measuring 35 ha as a result of an irregular boundary.
A 10 ha area adjacent to the Shilat farm has been set aside in the layout as a possible site for administrative and training facilities. It is envisioned that eventually offices, living quarters, and a lecture hall will be established within this area.
A 36 ha area has been set aside for a Shilat demonstration farm which shall be used for technology verification, training and demonstration. The layout of this farm was prepared by Shilat engineers. It consists of 8 units of 2,000 m2 ponds, 6 units of 3,000 m2 ponds, 10 units of 1 ha ponds, 3 units of 1.8 ha ponds and 2 units of 2.3 ha ponds. Altogether the ponds have a net water area of 24 ha.
Seawater shall be drawn from Khowr-e-Gasir, a tidal inlet located at the northwest corner of the 1,000 ha lot through a tidal canal with a bottom width of 50 m and a bottom elevation of zero. This main supply canal will extend all the way to the Shilat farm area. It will branch out into 3 secondary canals with bottom width of 20 m and zero bottom elevation and corresponding slope. Each individual farm regardless of size will pump their saltwater directly from the secondary canal, for distribution to the various ponds thorough a concrete lined canal constructed above dike. At each entry point, each farm will have the capability of adjusting the salinity using freshwater from another supply canal that is independent from the seawater canal.
Freshwater shall be pumped from Helleh River and delivered by a concrete canal to a 35 ha reservoir located along the southeast corner of the lot. This area has been selected because of its higher elevation. From the reservoir the water will flow by gravity through a concrete lined canal situated parallel to the secondary seawater supply canal. Each individual farm shall draw their freshwater supply for dilution through an open type inlet which interconnects with a stilling pool located at the head of the distribution canal. Mixing of saltwater and freshwater will take place in this stilling pool. The freshwater system assumes that a supply of 6 m3/sec is available at Helleh River. It is designed to provide 30 percent of total water requirement to attain a rearing salinity of 30 ppt. The seawater at the source inlet is assumed to have a salinity of 42 ppt.
The used water from the ponds will be discharged at Khowr-e-Ramleh which is located at the east corner of the pond about 3 km from the water supply inlet. From each farm unit, the used water will initially be discharged to tertiary canals which are designed as an internal system of each farm unit. From the tertiary canal the water will be collected through the secondary drainage canals which eventually merge with the main drainage canal. The size of the drainage canal have been designed to allow the simultaneous harvesting of 20 percent of each farm unit. This means in one day, a 5 ha farm can harvest only 1 compartment at a time, and a 25 ha farm, 5 compartments. Each pond is designed to be equipped with a monk type concrete drain gate capable of draining a 20 percent residual water in 4 hours. (In harvesting it is standard practice to slowly drain about 80 percent of the water the night before the scheduled harvest.)
It is envisioned that each farm will have as part of its support facilities, a pump house, a feed storage shed, a caretakers quarter and a multipurpose shed where nets can be mended, screens repaired and harvested shrimps washed and iced.
