During rainy season, floods often occur creating unfavorable weather conditions for shrimp farming: temperature changes during a day and widespread thunderstorms making abrupt changes in water environment, causing shock in shrimps and possible disease outbreaks.
1. Abrupt changes in environmental factors and aquaculture pollution causing shocks in farming species and leading them to stop eating, or even death due to infectious diseases:
- • Water temperature drops suddenly.
- • Rainwater is acidic or leaches out alum from embankments into ponds, which makes pH in pond drops suddenly.
- • Sudden drop in salinity (in brackish water farming)
- • Reduction of dissolved oxygen in the water
- • Reduction of alkalinity of water
- • Rainwater and flood water can leach out alum, fertilizers, plant protection chemicals and toxic waste from fields, orchards or residential areas into rivers, canals and farming ponds.
2. Farming species, ponds and cages can be lost or damaged due to:
- • Rising water level can overflow and destroy embankments.
- • Hurricanes, strong winds, big waves and flows can damage cages.
· Alkalinity suitable for black tiger prawn is from 90 to 130ppm, for whiteleg shrimp is 100-150ppm.
· Mix dolomite lime in fresh water for 24h, and then splash it into ponds at 8-10 P.M. at night.
· Each 1,655g of dolomite lime increases alkalinity of 1m3 water into 1 mg/ml.
· How to calculate the amount of dolomite lime: to increase alkalinity of a 5000m3 pond from 80mg/ml to 90mg/ml:
· The amount of dolomite lime used = 5,000 x 1,655 x (90-80) / 1000 = 82,75kg
· When increasing alkalinity of water in ponds, Viet Linh notices that only increase 1 time 10mg/ml then again, but not too much at 1 time because it will cause shocks in shrimp.
· If the method above does not increase or increases slowly alkalinity, we can use the following method:
· Combine 70% soda lime (NaHCO3) according to the above formula, 30% dolomite lime in fresh water for 24 hours; splash the mixture at 8-10 P.M. at night.
When salinity of the pond is lower than 8 ppt, blue-green algae often appears. Situations happen during that point:
• Algae are often blighted.
• pH changes significantly during the day
• Shrimps are covered with algae.
• The lack of oxygen in early morning often occurs.
• Shrimps with black gill disease and other gill diseases.
• Reduce feed.
• Use BKC 800 with 0,5ppm concentration. Apply it in 1/3 area of the pond, downwind without aerators.
• Take out algae foam that remains after applying treatments for ponds.
• Repeat 2 or 3 times these methods.
• Use probiotic with a combination of zeolite to absorb toxic gases caused by dead algae at the bottom of the pond.
In pond, turbid water is mainly caused by clay particles. Turbid water affects the following factors:
· Limit photosynthesis of algae in the pond; cause the lack of oxygen and high CO2 concentrations that increase shrimp suffocation.
· Algae are decimated suddenly
· Alluvium clinging in shrimp gills causes swelling or yellow gills.
Increase water changes in ponds and use probiotics.