Packing and transportation

Once harvested, careful packaging and transportation are important to maintain the quality of the PL. Usually, PL and juveniles aretransportedinplasticbags filled with water and oxygen (New 2002). In Thailand, PL are harvested from larval or holding tanks by using a large dip-net (0.7 x 0.4 m) and their numbers estimated before they are immediately packaged. Two thousand PL are allocated to each plastic packing bag (0.3 x 0.4m) containing 3 L of water. The bags are oxygenated for 3 to 5 minutes, after which the bags are closed with rubber bands. PL can remain in these bags for 24 to 36 hours during transfer to farmers' grow-out ponds, which are sometimes many hundreds of kilometres from the hatchery.

In Brazilian hatcheries, harvesting occurs after reducing the water level in the larval tanks. PL move around the sides of the tank and are captured using dip-nets. After the number of PL are reduced, the rest are harvested externally during final drainage of the tank. PL are then concentrated in a smaller tank with continuous aeration to facilitate counting. Before packaging, PL are counted using a volumetric or a visual standard. In the first method, the PL contained in a certain volume or weight are counted, and this number is used as a standard. The second method consists of counting approximately 2000 to 3000 PL, after which they are transferred to a light-coloured bucket filled with 5 to 6 L of water. Next, other buckets are filled with the same water volume and PL are placed in them, thus visually matching the number of PL in the counted container. Sixty litre plastic bags are used for packaging prawn PL at a density of 3000 to 5000 PL (10 mm size) in 12 L of water. The water is saturated with oxygen and a ratio of one-third water to two-thirds oxygen is maintained in each bag (Fig. 5.11), which is tightly fastened with an elastic band.

Vadhyar etal. (1992) found that introducing 10 to 15 mm pieces of floating translucent plastic straw as a habitat material in model transport containers for PL 10 to 15 M. rosenbergii improved survival time, compared to either no habitat, sinking black plastic ribbon or sinking white folded netting. With plastic straws, 100% survival was obtained after 72 hours at 100/L and 24 hours at 200/L packing densities.

In Thailand and Brazil, PL and juveniles are also transported in open plastic or closed fibreglass tanks (500-1000 L) containing 70 to 80% water, thus significantly saving materials and labour. With aeration, each tank can accommodate 300 000 to 500 000 PL. Usually, one- to tenton trucks are used fortransporting PL. A one-ton truck can

Fig. 5.11 Packaging postlarvae (PL) for transport.

accommodate about 500 000 PL in plastic bags. Generally, the prawns are transferred by night. However, if the transport occurs during the daytime, additional precautions are necessary. The floor of the truck is lined with gunny-sacks, which helps to prevent heat transfer from the road and from the truck exhaust system. A temperature of 20 to 27°C is maintained by placing new supplies of crushed ice on top of these sacks every 2 to 3 hours; this ensures a high survival rate during transport. Sometimes trucks with built-in cold storage are used to transport 1 to 2 million PL at a controlled temperature of 20 to 25°C. A stable water temperature during transport is essential for success. Schmitt & Uglow (1993) showed that sudden changes in temperature appear to cause stress, as exhibited by increased nitrogen efflux rates. Similar stress is caused by handling. In Brazil, either surface or air transportation is used to distribute PL. For transportation periods of more than 6 hours, the temperature is kept between 20 and 22°C, in order to reduce metabolism rates (oxygen consumption and ammonia excretion) and, consequently, cannibalism.

How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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Responses

  • katie-leigh
    Why chilled water used in transportation of shrimp pl?
    4 months ago

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