Oyster hatchery at Narakkal

As one of the largest oyster hatcheries on the west Coast, the Narakkal Oyster Hatchery produces a oyster larvae for use in oyster training, oyster cum farming, and educational projects. Over the past two years, spawning oysters at the Narakkal Lab Oyster Hatchery have resulted in the deployment of over 70 thousand oyster spat which is transported to the waters of the Muthakunnam farming sites in the hopes of developing farming technology and restoring the health of the estuary. Cultchless spat of edible oysters are also produced in the hatchery at Narakkal. Spats settled on the polyethylene sheet and clam shell grits provided in the tanks grows uniform shape. These uniform shapes of spats or juveniles are transferred to farm to get larger ones of uniform shape which fetches good price to the farmer. This uniform shape oyster has very good demand for live consumption in high-end restaurants.

Fig.1. Spat settled on the shell grits		Fig.2. Spat settled on the polyethylene sheet
Settled oyster spat in the empty shell

Descriptions

Broodstock Conditioning System

In the Narakkal hatchery, oysters are brought into the temperature controlled broodstock conditioning lab and cleaned of fouling organisms like barnacles and mussels, and scrubbed to remove any dirt or mud, then placed into specially constructed tanks designed for holding adult oysters for use as broodstock. Gonadal development is accelerated by the addition of heated water or delayed by adding chilled water.

Conditioning tanks

Algal Culture System

Several species of algae are maintained in the algal culture system of the hatchery viz. Isochrysis galbana, Pavlova lutheri, Chaetoceros spp.etc to feed oyster larvae and young spat. Algae cultured in the hatchery are very small (2-10 microns). Older spats are not fed due to the larger quantities of algae needed, so they are transferred to the Muthakunnam farming site for growing adults, However, broodstock oysters are given algal feedings to enhance gonad production.

Algal culture –for feeding oyster larvae

Culture techniques

    Algae are grown at the hatchery for different purposes. Stock cultures are grown to provide a supply of starter cultures for inoculating large scale cultures. The large scale cultures are then used to feed the oyster larvae. When growing algae for the hatchery at all scales of culture sterile water, nutrient media, light, air, and CO2 are needed.

    Our hatchery has two sizes of stock cultures, 125ml, 2l and 4l. The 125 ml flasks are only used to inoculate new stock cultures every three weeks. The larger 2 and 4l stock cultures are used to inoculate the mass scale of cultures. Since these cultures are used to start all other levels of cultures, they need to be kept sterile.  250 l mass algal cylindrical tanks are used to provide large scale cultures. After being inoculated with one or two flasks (2l), the algae blooms for about 4-7 days until it attain a density of 4-6 million cells/ml and are used to feed the oyster larvae.  Mass culture of algae is semi-continuous cultures type. Semi-continuous cultures are only partially harvested, then refilled with sterile water, nutrient media is added, and the same culture is allowed to rebloom.

Larval rearing facilities

The hatchery is equipped with complete larval culture facilities. These facilities included one tones fiberglass tanks, filtered seawater, different larval size graded sieves, tubs etc.

Larval rearing section

Farming and Processing unit at Muthakunnam

Muthakunnam village has both farming and processing units. The farmed oyster production was 3200 tonnes during the year 2011-12.  The farmed oysters are processed in processing unit at the village itself. The processing units are equipped with facilities included sea water purification, jet washing facility, depuration unit, automatic heat shucking unit, small microbiological lab etc.

    A common village facility such as depuration and heat shucking unit are developed under NAIP. A depuration unit (3000 oysters per run of 12hrs in specially designed tanks) operated by farmers has been supplying depurated oyster to high end restaurants in Kochi city @ 500 oysters per week. The depurations will benefit the farmers since they can assure quality of the oysters and increase the profit margin. The depurated oysters are heat shucked in the automatic steam unit thereby ensuring high quality/ purity of the product. The unit can heat shuck 100 oysters per 6 minutes using steam.  This was a new method which reduced physical drudgery to the women farmers and farmers discontinued the conventional method of heat shucking which was more labour intensive.

Oyster farmers preparing seed collection units		Farmers bringing harvested oyster to VAP unit
Fig. Depuration of oysters in the village depuration unit		Semi automated heat shucking unit

 
Depuration display unit (DDU)

A depuration display unit (DDU), transparent display unit, is developed under NAIP for live oyster trade in high end restaurants and thereby ensuring consumer confidence especially international tourists. This has facilities for water storage and purification where 250 oysters can be maintained in live condition. This has helped the farmers to get Rs 5 per oyster.

Depuration display unit developed under NAIP