Aquaculture environment-hardness and dissolved oxygen

Characteristics of low hardness water bodies

Poor growth

Skeletal dysplasia

Low survival rate after molting

Tolerance of cultured animals to low hardness

Hardness is the sum of all divalent cations in water, mainly including calcium and magnesium ions. Generally, problems occur more easily in freshwater farming than in seawater.

Hardness (mg/L CaCO3) impact

≤50 Low pond productivity

50-100 High pond productivity

100-250 Productivity is usually highest

Hardness Management

overview Since the hardness of most seawater is greater than 6000mg/L CaCO3, there is generally no need to worry about the hardness of water in the seawater environment.

The application of a fine-grained calcium-containing limestone-like substance, usually standard for improving water hardness in freshwater systems.

gypsum Gypsum (calcium sulfate) is another commonly used substance to improve the hardness of water, gypsum purity varies, but the application of pure gypsum 1.72mg/L can increase the total hardness of 1.0mg/L. Such substances should be applied slowly to the water until the water reaches the appropriate hardness.

mineral feed When the mineral content of water is low, feeding higher mineral content feed will also contribute to the health of breeding animals.

Characteristics of inappropriate dissolved oxygen content in water

Dissolved oxygen too low

Animals eat poorly

Poor growth

Fish upstream to the surface

Not very active

More susceptible to disease

Shrimp molting times reduced

Fish congregate near aerolite

Shrimp concentrated in shallow water

Increased operculum movement

Death

Water color changes dramatically

Dissolved oxygen too high

(Bubble disease and its symptoms can also be caused by high nitrogen concentrations)

Bubble under skin

Death

Exophthalmos

Shrimp: fast swimming; floating on the surface of water; air bubbles on gills and epidermis

Tolerance to Dissolved Oxygen in Cultured Animals

Tolerance levels are generally recommended and are strongly influenced by several other interacting factors. Recent feeding patterns, high activity levels, parasites on gills and environmental stress due to poor water quality can cause dissolved oxygen problems, even if dissolved oxygen appears to be in the appropriate range. Oxygen solubility (the amount of oxygen dissolved in water) decreases with increasing temperature, salinity, and altitude.

Effect of dissolved oxygen level on warm water fish

Dissolved oxygen (mg/L) impact

20.0-30.0 Bubble disease is prone to occur

Management of dissolved oxygen

overview

change the water Water exchange with oxygen-enriched water is sometimes an option, but only for small bodies of water, and oxygen-enriched water for exchange is readily available.

mechanical oxygenation Mechanical oxygenation is the most common method of oxygenation in aquaculture. In high density aquaculture system, mechanical oxygenation should be used continuously. Mechanical oxygenation can also be used as an emergency measure in other cases.

feeding Reduce feeding rates as feeding increases dissolved oxygen requirements.

activities Animal activity and environmental stress should be minimized and, if possible, capture should be avoided.

stocking density Reducing stocking density is also a solution when dissolved oxygen problems occur frequently.

Circulating water tank system

Pure oxygen (liquid or gas) can be added to small water bodies, but care must be taken to avoid excessive dissolved oxygen in the water body and possible bubble disease.

runway pool system

water inlet If the water source is located higher than the pool water, increasing the influent can increase dissolved oxygen, and if the influent dissolved oxygen is not high, reducing the influent can reduce the dissolved oxygen requirements associated with fish activity.

water spray Running water over rocks, fences, or other objects increases dissolved oxygen in the water before it enters the runway pool.

pond systems

Algae and plant biomass should be maintained in the water to prevent dangerous and drastic changes in dissolved oxygen, which are usually most serious at night.