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| Keeping live prawns alive longer. |
The 2 main causes of prawns to perish in the baitwell are Asphyxiation and Nitrogenous poisoning. The 3rd cause, Trauma and Predation, is self explanatory. Therefore, to keep prawns alive, you just have to either remove the 2 main causes, or to find a way to limit the effects of these causes. And giving the prawns enough space to fulfill the 3rd.
CAUSES
Asphyxiation can come from depletion of oxygen in the water they breathe or from the malfunction of their gills. More on this later.
Poisoning usually is the result of excess Ammonia in the water because of their excretion (urine and feces) or Nitrite which is the result of the decomposition of Ammonia, whose trace amounts are usually already present within the water which the prawns are bagged in.
Ammonia causes their gills to burn out and so they display symptoms of Asphyxiation even though you might have a powerful air pump giving all it's got thru the limewood diffuser.
Nitrite just attacks the central nervous system paralyzing them and it's dead in a jiffy.
METHOD
To effectively remove Asphyxiation and Nitrogenous Poisoning, the best way is to continuously change the water they are kept in - that means keeping them is a basket floating in the sea.
Where that is not possible, you'd need to have an appropriate sized protein skimmer (used in marine tanks) set up for the baitwell. Other ways which are less effective but do contribute to lessen the casualty count are: Dilution and by Chemical Neutralization.
Having a bigger baitwell with more water, or having less prawn density in the water will result in a more dilute solution of Nitrogenous waste in the water. It also lessens predation and trauma which over stocking often results in. Getting a spare bag of water to dilute the baitwell's water regularly is another way - just drain off half and top up.
Using chemicals that neutralize the Nitrogenous wastes by locking up the effect of Ammonia and Nitrite can also help. Seachem Prime (http://www.seachem.com/Products/prod...ges/Prime.html) is one such product that claims to do this.
APPLY BASIC PRINCIPLES
Understanding that prawns are cold-blooded, lowering the temperature of the water they are in will also lower their metabolism. They go to sleep literally, so there is less excretion, less usage of oxygen, and even no predation. Chilling the water is effective in achieving this. However, at temperatures colder than 15 ̊C
, your prawns may not wake up from their sleep at all, so do not be over enthusiastic with the chilling, and bring the temps down gradually.
As far as is possible, a wide and shallow baitwell is better than a narrow and deep one. Wider areas give more livable space for the prawns and allow better gas exchanging surface area.
Lastly, offer the prawns something to cling onto. Some leaves and twigs, a raffia mop etc all give the prawns something to cling onto, as long as they are neutrally buoyant. This achieves several benefits: It slows down their physical activity as they can cling on and rest instead of frantically swimming in a smooth baitwell as their feet cannot find purchase on the slick surfaces of the well. It also psychologically expands the area of the baitwell, as they can hide from each other, lessening the chances of predation and trauma; and it expands the usable real estate in the baitwell by allowing the prawns to rest at all depths of the baitwell instead of stacking over each other at the bottom.
PRACTICAL USE
In the past, where the battery operated air pump was not known of, how did we transport prawns alive? We could actually cast net for the prawns, then take them dry, across the JB immigration and have them still alive and kicking when we put them back into the water some hours later. Here's how we did it:
We laid a layer of ice cubes on a shallow wide tray and covered that with a thick layer of newspaper dampened with sea water and then squeezed dry. A plastic bag of ice is put in with the pail of prawns to make them sleep. Then, the prawns are comfortably drunken, they are obedient enough to be laid out neatly on the newspaper, and another layer of damp newspapers covered over them. Finally some plastic bags of ice cubes are spread thinly on top to keep the top cool. By doing this, we can transport the tray without seawater and suffer almost no casualty when we revive them in the sea 4 hours later.
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This write up was contributed by Lawrence Lee aka LLCC. |
