Stocking

Stocking involves a number of crucial steps, from the time of procurement of the seed stock/ fingerlings until the seed stock are introduced into the grow-out ponds. The process of seedstock selection (hatchery visit, transportation and screening) should be done at least 2 – 3 days prior to stocking.

Step 1: Procurement of seed stock

Procurement of seed stock is one of the crucial steps in any form of farming. Often farmers tend to procure the required seed stock from the same hatchery, year after year, based on a number of perceptions that the seed stock are of good quality, reliability in supplies, easy accessibility reduced transportation costs, affordable price, and the long-established business partnership, which even perhaps permit credit.

Catfish seed stock, unlike in the case of shrimp for example, until now donot need to be tested for any specific pathogens. However, it is advisable to evaluate the performance of the seed stock on a yearly basis, for growth, yield and percent mortality not only in your farm but also that of the adjacent farms. In this manner an evidence based judgement can be made as to whether, there had been a deterioration of the seed stock over the years and if so steps to seek alternative supplies of seedstock can be taken.

Step 2: Choosing seed stock

At each procurement it is essential that the farmer visits the hatchery/ nursery operation and obtain a full history of the potential procurement. The details to be obtained are:

• How many female and male broodstock were used in the spawning and the approximate ages of these animals
  
• The number of times the female broodstock have been used in the current spawning season, and if more than once, which spawning the current seedstock originate from (for example first in the year or the third in the season)
  
• Ideally, the farmers should procure seedstock from females that are 3-5 years old spawn no more than twice a year.
  
• Spawnings that have resulted in average or above average fry to fingerling survival
• The seedstockare active, and show no signs of any abnormal behaviour nor any signs of disease or physical damage
• The seedstock are properly weaned
• The seed stock are of uniform size.

Step 3: Transportation of seed stock (fingerling)

The science of seed stock transportation is well developed, for many species, and lessons can be taken from these experiences for the catfish farming sector. The selected seedstock, should be starved the day before being packed for transportation. In the Mekong Delta, catfish seedstock are mostly transported by boats in which water is continuously pumped through the transport tanks. The transportation of fingerlings should be done in the early hours of the morning and away from direct sunlight. In addition, land transportation may be used for seed transportation, particularly fro short distances from farm locations.

The total duration of the transportation time from the nursery to the grow-out farm should be, ideally less than 6 hours duration, and during transportation, care should be taken to minimise direct exposure of the containers to sunlight - to avoid sudden increases in temperature.

Step 4: Acclimation and release of seedstock

On arrival of seed stock to the farm site the containers should be placed in the grow-out ponds (or special large tanks that could be used for this purpose), unopened, so that the water temperature in the pond and the containers are balanced. Sudden and immediate release of seedstock to the pond should be avoided. The pH and the temperature of the containers are the same as that of the pond- water the seedstock can be slowly released into the ponds, in batches. Here again care should be taken that these operation are not carried out in direct sunlight, and preferably done during the period when the sun is setting. At the place of release of seed stock, salt can be used as a disinfectant. Do not feed the released seedstock on the day of stocking; so as to permit time for the seed stock to acclimatise to the pond environment.

Feeding should initially carried out at a very low level, approximately 1 % of the body weight per day of the stocked fish, for three to four days, and then raised gradually to 3 to 5 % of the body weight per day.

Step 5: Stocking densities

The catfish farming sector in the Delta is one of the most intensive aquaculture practices in the world. The deep ponds,regular water exchange and the ability of the catfish to breath air permits this intensity of stocking. The stocking sizes range widely: 1.0 to 8.5 cm (mean 4.5 cm) as fry or 1.2 to 20 cm (mean 8.6 cm) as fingerlings, depending on the nature of the practices. The survey results also indicated that the stocking densities used (SD) ranged widely:

8-125 fish/m² (mean 48 ± 2.1 se) and 5-31 fish/m3 (mean 12 ± 0.5 se), depending on the size and availability of seedstock and the financial capacity of farmers to purchase seedstock.

The survey results show that the yieldin the farms increased linearly in relation to SD. However, it is suggested that the SD should not exceed 80-100 fish/ m² and/or 18-22 fish m³.

Updated on : Feb 2015