Luminous bacterial disease: It is caused by Vibrio harveyi / V. Therefore it is very much essential to disinfect to reduce or remove the bacterial load in the culture water.
In practice, disinfection is commonly adopted in hatcheries as a separate treatment measure. This filtration is effected by designed filters and filter materials that are non-toxic and non-corrosive. There are physical filters and biological filters with the application of biological principles such as Nitrification for removal of Ammonia in the rearing water.
Fungal disease
Mysis stages are most vulnerable to fungal attacks. Heat exchangers of some hatchery systems raise the water temperature to a level that is intolerable to some microbial pathogens. Heating of water is suitable only for smaller systems.
This is the physical removal of debris and other solid material that is present in suspension and is mainly used to remove solids from supply water. This solid removal also helps in the reduction of microbial load associated with those solids in suspension. It may choke the gills affecting respiration. Use of detergents will also help in the removal of nutrient base that will encourage the growth of microbes.
ii) Heating :
This is very common method of disinfection that will help in reducing the microbial load in any system or component. Beculovirus group affect mid gut and hepatopancreas whereas parvovirus group (IHHNV) affect epidermal, hypodermis & mesoderm.
4. Disinfection can be accomplished by using one or a combination of readily accepted methods. alginolyticus. The uneaten feed is another fraction to add with the fecal matter offer good scope for the growth of microbes, as they are the principal feed for the heterotrophic bacteria. This feed results in the production of fecal matter by the fishes. Infected larvae exhibit continuous greenish luminescence when observed on total darkness.
Vibriosis: It affects haemolymph and mid gut gland.
Bacterial Necrosis: It starts on the antennae or uropod in protozoa III or pleopods in mysis. In this process a variety of hatchery system components are to be subject to disinfection, like equipment such as pipes, tanks, bio-filters, nets, floor, boots, culture water, input water, food, stock and air, output of effluent, debris and dead fish, etc.
What is Disinfection?
The technique or method of selectively controlling or removing organisms that enter into aquaculture system is called disinfection. For this the hatchery should be disinfected and shutdown between production cycles so that the pathogens will have no host to infect and will get eliminated from the system. The common fungae that attack the shrimp larvae are Lagenidium.
3. This may cause high mortality in post larvae. Hepatopancreas and stomach become greyish and hence called grey stomach disease.
2. Though they are not directly pathogenic, they can cause mortality in larvae.
Disinfection in Hatcheries
During the routine operation of hatchery, many pathogenic microbes may accumulate in the equipment and components of hatchery system. It can be said that a perfectly designed biological filter will keep the water free from ammonia and mortality due to ammonia.
iv) Dehydration
Dehydration or drying and reducing water contact of equipment or entire system provides a degree of disinfection. Drying easily destroys fragile stages of many parasites and dry surface have greater exposure to the effects of ultra violet light.
v) Radiation
Disinfection by radiation is especially used in hatcheries. The ultraviolet light of approximately 2500-2650 Ǻ wave length effectively destroys vegetative stages of many pathogens such as virus, bacteria and fungi. During water disinfection by radiation, pretreatment such as sedimentation and filtration make the water suitable for UV radiation treatment, by removing the hurdles for penetration of UV light. The ultraviolet rays are used to disinfect the organisms in limited dose. The dosage depends on intensity of light, duration of UV-light on organisms.
Chemical methods
i) Chlorination
It is commonly used method for disinfection of water in shellfish hatcheries. The water is treated with 0.2-0.5 mg Cl2/litre of water for 20 to 30 minutes. The removal of residual chlorine prior to introducing the disinfected water into shellfish hatchery is inevitable.Vigorous aeration was given to remove the residual Chlorine present in water or it is passed over charcoal for removal of chlorine. If any chlorine residue is present in treated water, it is toxic to shellfishes. Chlorine in the form of calcium and sodium hypochlorites and chloramines are commonly used. Nowadays chlorine-dioxide is also used as disinfectant, which is considered as safe as it seldom leaves any residual chlorine in harmful form.
ii) Ozonation
Electric discharge and UV radiation of a suitable wavelength produce a 3-atom form of Oxygen (Ozone). The contact concentration of Ozone is around 3 mg/ liter of water with residuals of below 0.15 mg/ liter. The residual ozone may also be removed with charcoal prior to use. However, the cost of equipment and use is relatively high.
iii) Formalin and Formaldehyde
Formalin water containing dissolved Formaldehyde is a readily available industrial Chemical. A 1:100 mixture of formalin and water is used to disinfect the water. Formaldehyde [HCHO] gas has been used for the disinfection of sealed building, usually generated by heating Para formaldehyde and the polymerized solid of Formaldehyde. It is effective against many viruses and bacteria.
iv) Quaternary Ammonium Compounds [QAC]
QAC are widely available in numerous brands and strengths. The active concentration is approximately 1200 mg/ liter (1200 ppm) of water. It is effective against gram +ve bacteria, some viruses but less effective on fungi and gram -ve bacteria.
It is clear colorless, water like in appearance, has pungent odour, and do not highly corrosive or dangerous toxic effect.
vi) Iodophores
Iodophores are generally available at 1% solution. They are organic compounds that release free iodine. The active concentration for disinfection of water is 50 mg/ liter and for equipments 250 mg/ liter. It effectively disinfects bacteria and some viruses.
During unfavourable and lean demand periods have to be advantageously utilized for the purpose of disinfecting the entire shellfish hatchery. The affected areas get melanised. To minimize the outbreak and transmission of disease causing organisms and parasites, disinfection is becoming one of the promising methods in the super intensive aquaculture system
Disinfection has widespread application as a method of sanitation, to eliminate or suppress the presence of the initial infective unit that is the pathogens. The tanks and other equipments are scrubbed with brushes or scrub pads of various designs. When there is any drastic change in water quality favouring the microbes, it will enhance in number and prone to cause disease to culture organisms. Therefore disinfection has to be done in all possible ways to completely avoid the infection. This can be enhanced by using standard detergent powders to inactivate the organism even if they cannot be removed. The basic idea is that the temperature above certain level would kill the microbes by dehydration of the cells. It is mainly used for equipment disinfection. Viral disease
They appear mainly during post larval and juvenile stages. The best method to avoid the infection is the breaking the life cycle or continuity of such pathogens in the hatchery. In the process of disinfection, the unwanted microorganisms are removed from the water.
Methods of Disinfection
Disinfection is broadly classified into two methods.
i) Physical Method
ii) Chemical Method
Physical Method:
i) Cleaning
The cleaning removes sessile organisms. Larval fouling
Large scale infectation of Zoothamnium, Vorticella etc on the gills, eyes of larvae lead to hypoxia and death. Bacterial Diseases :
It affects zoea, mysis and post larvae. The nutrients released or leeched from the feed and fecal matter also encourage the growth of diverse microorganisms. This is to ensure non-settlement of microbes in the system.
In hatcheries, the major input is the formulated and prepared feed for the breeders and larvae, which is purely organic in nature. In many instances these microbes turn to be pathogens causing or leading to disease outbreak in the population.
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