Measuring control in Aquaculture Biosecurity

Biosecurity is the management practices that prevent non-infected, healthy animal
populations from being exposed to infectious or parasitic agents. Common biosecurity
measures include:

1. Sanitation:
                       Sanitation includes the cleaning and disinfecting of hatcheries, holding facilities, tanks, ponds, handling and vaccination equipment, etc. Cleaning must be done before disinfecting. Disinfectants include chlorine, heat, steam, formalin, and other chemical compounds. All of the chemical disinfectants are toxic, so all equipment should be rinsed well after disinfecting.

2. Vertical disease transmission:
                       Vertically transmitted diseases (from parent to offspring) can be prevented by using healthy, disease-free broodstock.

3. Egg disinfection:
                        Egg disinfection with iodine or other solutions at the time of the water hardening of eggs can reduce the incidence of disease problems of eggs and larvae.

4. Traffic:
                        Restricting people and equipment traffic can reduce the chance of disease transmission from one facility to another.

5. Water treatments:
                        Water treatments of incoming or recirculating water decreases the chance of pathogenic organisms entering the culture system. Treatments include mechanical filtration, UV light, and ozone.

6. Effluent treatment: 
                         Treatment of wastewater from aquaculture facilities and processing plants reduces the release of microorganisms into the environment. This is important, because there have been problems in the past with diseases re-entering an aquaculture facility from wastewater of a processing plant. Infected water from the plant was released, and then this water was taken into the aquaculture system.

7. Clean feed:
                         It is important to use clean, fresh feed. Proper handling and storage of feed can reduce food-borne disease organisms.

8. Disposal of mortalities:
                         The proper disposal of mortalities by incineration, burial, or composting will reduce the risk of recycling diseases. It is also important to remove dead fish from the tank or raceway often to reduce the likelihood of spreading the infection.

One of the challenges faced by aquaculturists is to offer all the life stages of their animal’s
proper sanitary conditions and Biosecurity. A comprehensive biosecurity program should be
in place. This is essential in combating and preventing disease.

With the rapid increase in intensive aquaculture, the need for disinfectants has also increased.
Entry and growth of pathogens must be minimized through use of disinfectants in water, on
tanks and equipment, and on eggs. Disinfectants used in aquaculture are aimed at all types of
infectious agents (including bacteria, fungi, viruses and protozoa). Disinfectants kill disease causing
organisms by releasing proper amounts of chlorine or iodine or other compounds.

A Proliferation of Pathogens

Pathogen. The word conjures up horrific thoughts of plague and death. It comes from the
Greek word for ‘feeling’ or ‘disease’. It comes from kids with snotty noses that you pick up
from daycare. They got it from some other kid whose parents aren’t as diligent about
hygiene. Simplistic maybe, but the principle is the same whether it is people or fish:
pathogens are transferable and they get that way by making copies of themselves.

Pathogens are organisms that cause disease. They can be viral, bacterial, fungal or parasitic.
On the size scale, viruses can be nanometers wide (millionths of a millimeter) and only
visible with an electron microscope, while bacteria are microns wide (thousandths of a
millimeter) and visible with light microscopes at high power. Fungi and parasites are both
macroscopic and microscopic.

The common aspect among all of these pathogens is that when present in large enough
numbers, they produce toxins, disrupt cell function, or overuse resources of the host while
feeding their own needs to reproduce. Not a pleasant thought.


Most viruses enter the fish by the mucosal linings of the gut or skin or by entering through gill tissue that has a thin cell membrane and a high surface area. In the gut the virus must survive acid conditions and then enter surrounding tissues to become infectious. In the fish slime, it must survive wandering macrophages (scavenger white blood cells) and at the gill sites, it must pass unrecognized by other white blood cells. If all this is done, the virus can initiate infection.

Once inside the fish the virus must then enter a host cell that permits replication. This is done
by commandeering the machinery for normal DNA replication and using it for it’s own evil
purposes. After doing this, it makes several million copies of itself until the cell is full, bursts
and spreads viral particles to other cells, either within the host or sometimes, outside the host.

The virus can relay it’s disease attribute by cell lysis (disintegration), producing a toxic
substance, changing host cell function or inserting a bit of it’s genetic material into the cells
genome. The most common observation is cell lysis as the virus multiplies in number.


Bacteria play the numbers game too. They enter the fish by the same methods or by open wounds suffered through trauma. Once inside, bacteria use the fishes’ plumbing system, find a tissue that
it likes (specific or non-specific) and sets up shop. Here the buggers multiply rapidly. The disease aspect of the bacteria is directly by tissue damage or by production of toxins. These toxins may be a result of metabolism or as a mechanism to protect the process of replication. The latter is almost a defense mechanism at the bacterial level. Either way, having too many bad bugs share your body is not a good thing.


Fungi, like some other pathogens, are opportunistic, and are sometimes secondary infections to other fish health issues. Fungi send out hyphae (filaments) to attach themselves to nonspecific tissue that may be vulnerable or susceptible. From there they multiply spreading throughout the tissue utilizing the hosts valuable energy resources.


Parasites may use fish as an intermediary or primary host. As an intermediate host, the fishes’ chances of overt disease signs are small. However, as a primary host, the fish is the environment the parasite has been living for. Parasites don’t generally kill the host, but they tend to alter behaviour and growth. The idea of having a macroscopic bug thriving to reproduce in you is not a pleasant one and it is easy to understand why the fish looks sick.


Got an infection? Take a pill. But how does medication kill bugs? Antibiotics – those chemicals that kill bacteria – are also called antimicrobials and are of two general types: bacteriostatic and bacteriocidal.

Bacteriostatics prevent the bacteria from multiplying by inhibiting cell division. The fish then has time to develop an immune response and finishes off the resident bugs using its own defense system.

Bacteriocidal medications kill the bacteria outright (how?). Antifungicides have similar effects on fungi by either inhibiting growth or by making changes to the cell wall and membrane of the fungus’ hyphae. Poking holes in the cells of fungi causes salt and ion penetration that kills the cell and hopefully the fungus.


Parasiticides are usually specific in toxicity to the target organism. The real challenge here is to kill the invader while keeping the host intact. These compounds usually focus on some particular feature of the parasites’ anatomy or biology and exploit that weakness. On the good side, pathogens don’t normally live long outside a host. This is because they are dependant on a host for most of the necessities of life. Some may aestivate (go dormant) as spores or such, but generally they die. This is also the time to disinfect. If the pathogen is outside the fish, it’s much easier to kill it. Not only is the environment bad for the pathogen, there are also more tools that can be used to kill it. Selective toxicity is not necessary because you have isolated the pathogen and do not have to worry about the host. This is the principle of disinfection.

A good disinfectant will kill the pathogen and prevent growth of new pathogens. Of course,
in a hatchery or farm situation, the disinfection process must be safe for humans, fish and the
receiving environment otherwise some really nasty stuff could be used. Such uses would be
irresponsible. The idea is to have a disinfectant that works with the efficiency of nuclear
warfare, but without the aftermath. Biosecurity on fish farms has always been a challenge but
there is no better time to kill a pathogen then when it is exposed, vulnerable and in search of
a host.

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