Fish Nutrition and Feed Technology (2+1)

Unit 18 - Feed Management

18.4.Factors affecting feed net consumption

(1) Deteriorating water quality

• The deterioration of water quality may arise in below enlisted situations.
• Following a crash of the plankton bloom which results in low oxygen and increased production of decomposition.
• After prolonged period without water exchange.
• After period of heavy rain causing increased turbidity or a drop in pH.
• After prolonged period of low sunlight leading to low levels of planktonic photosynthesis and low oxygen.

In any of the above cases there will be a drop in daily feed consumption.

(2) Deteriorating pond bottom condition
Deteriorating pond bottom conditions can lead to poor water quality and disease but it can have more direct effect on feeding. If the clean area of the pond bottom is significantly reduced, then the number of shrimps in the feed nets may increase and the feed will be consumed more rapidly in feeding nets. Due to poor pond bottom condition shrimps will have abnormal discolouration of the gills, external foulings, swollen tail, cannibalism and broken appendages.

(3) Diseases
Serious disease outbreaks in pond leading to poor pond bottom and shrimp surfacing in water and moving round in the edges of the pond will certainly affect the feeding behaviour.

(4) Compitators in the pond
Competitors in the ponds compete for feed consumption and results in less utilization of feed by the shrimp and ultimately shows high FCR and size variation in the shrimp population.

(5) Quality of the feed
Several aspects of feed quality can affect the consumption of feed in the feed net. If the food is changed and the texture or consistency is different, the shrimps will take a couple of days to acclamatise to new feed. If the feed have a less stability then the result in feed net can be confusing. If the feed do not have enough attractants then the shrimp may not feed normally.

(6)Moult cycle
There is a substantial reduction in feed consumption during the moulting periods. Majority of the shrimps moult, 2-3 days prior to the full moon or new moon. Some time due to water exchange in the ponds, majority of shrimp population moults. During such periods only 50 -60% of feed should be given in the ponds, depending on the feed net observation.

(7) Temperature and Salinity
Temp can also affect the feeding behaviour of the shrimp. Typically if the temperature is higher than 32 to 33 0C or below 25 0C, then the feeding response will reduce by 30-50%. Shrimps are more seriously affected by sudden change of temperature rather than gradual change.