greenhouses I shade net I hydroponics I aquaponics
Purging is the processes whereby fish are held in clean water and not feed for a period of time. Purging is a useful protocol employed by fish farmers to reduce the stress on fish during handling and transport, and to minimise unpleasant flavours in the fish’s flesh.
period of time prior to size sorting,
Aquaculture techniques:
Purging Fish
P
urging is the processes whereby fish are held in clean water and not feed for a period of time. Purging serves two primary purposes: • Reducing the amount of faecal material in the gut which reduces the level of stress encountered by the fish during handling or live transport, and • Reducing or removing off flavour in the flesh prior to slaughter.
harvesting or transporting them, we reduce both the oxygen shortage and metabolite toxicity stressors, allowing the fish to travel and arrive in a far healthier state. The primary factors determining the duration of purging for handling or
Purging for handling or transport Digestion utilises oxygen. As such, if fish are handled or transported after normal feeding they experience increased stress during handling as well as transport, as the body struggles to obtain adequate oxygen from the water for digestion and dealing with heightened stressors. Furthermore, normal feeding is followed by normal rates of waste excretion from the body, which can quickly pollute the transport water, adding yet additional stress. By withholding feed for a limited
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transport are the size of the fish and the duration of the handling or transport event; small fish and shorter time periods require less purging. Small fish may require 6 hours of purging prior to handling or overnight purging prior to a 12 hour long trip. Larger fish going on a 24 hour trip may require 3 days of purging prior to being packaged and shipped.
Purging for slaughter The feed that fish consume and quality of water in which they live, can impact its flavour. As such, normally fish is purged prior to slaughter in order to evacuate their gut as this lessens or removes the off-flavour associated with feed. In addition, hold the fish in clean water for the duration of purging to rinse out water borne flavour affecters. By doing these two things simultaneously for 24 to 72 hours you are able to get rid of all unpleasant tastes in the flesh. Clearly you need to know why you are purging your fish in order to apply the more appropriate method of purging them. Systems differences Most fish species cannot be purged in earths pond as they will find food to eat in the pond even though all artificial feed is withheld. The exception would be predatory species such as trout or eels that will not be able to find appreciable quantities of feed and can be purged reasonably effectively in ponds. Cages in a green water environment are similarly ineffective for purging fish that feed low on the food web as they can find some feed in the cage and importantly the green water still results in off-flavours persisting.
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