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Prawn growout and harvesting

Growout

Pond preparation

Between harvests, the pond bottoms are dried and waste and sediments from the previous crops are removed from the centre of the ponds. The sand bottom is renovated and dried and some extra sand may be added. Prior to filling the ponds are limed. The ponds are then filled through screened inlets and left for 7–10 days before stocking.

Organic fertilisers are used to maintain healthy algal blooms. These blooms are essential to achieving good survival and fast growth rates.

Stocking rates

Kuruma post larvae are generally stocked at 30 post larvae per square metre with a range of 25–60 per square metre.

Feeding

Careful feeding is necessary to achieve viable production. The prawns are fed 2–3 times at night and feeding trays are used to more accurately monitor feed rates.

The major component of kuruma artificial feed is an expensive mix of high protein fish and squid meal. The prawn diet is presented in a pellet form that is water stable and of a size suitable for the particular growth stage.

Food conversion ratio (FCR) for kuruma prawns is usually around 2.5kg of feed to produce 1kg of prawns (FCR 2.5:1).

Within 6 months, the prawns reach marketable size. With good survival (greater than 80%), production of 3–4t per hectare can be achieved.

Harvesting

Harvesting normally starts in March–April and continues through to July–August.

The crop is normally partially harvested by using traps or wing nets set at night when the prawns are active. The traps are baited and the larger prawns are trapped inside while the smaller prawns escape. The wing nets channel the swimming prawns into a tunnel and then into a box net.

Prawns are slowly cooled in two stages down to 12–14oC before packing. The graded prawns are then packed in cool, moist wood shavings or sawdust in 1kg packs. These packs are then placed in insulated boxes, which maintain the 12–14oC range, and flown to Japan. Survival rates of 95% can be achieved using this technique.

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