Читать книгу Fundamentals of Aquatic Veterinary Medicine - Группа авторов - Страница 55

Insecticides may be used in the local environment for the control of agricultural pests or insects that cause vector borne diseases. These compounds can affect fish through runoff and atmospheric accumulation on pond surfaces. There are many types of insecticides on the market. Most insecticides affect the neurologic system using different mechanisms of action. They may affect acetylcholinesterase activity, block sodium channels, bind nicotinic receptors, affect the peripheral nervous system and directly degrade neurotransmitters in several other ways. They can also cause chromosomal aberrations, decrease protein levels, affect the immune system, and mimic or block reproductive hormones (Sabra and Mehana, 2015). Compared with insects, they differ in their specificity for vertebrates, their toxicity, their bioaccumulation, and their environmental persistence.

Organochlorines have been banned in most countries due to their highly toxic nature. They are toxic to most animals, have a high level of bioaccumulation, and persist in the environment for long periods of time (Fulton et al., 2013).

Organophosphates have a lower level of bioaccumulation and a shorter half‐life in the environment. They may be used as a treatment for several fish parasites, but can be easily overdosed. Some fish are more sensitive to organophosphates than others. If using organophosphates for treatment of disease, always determine the species sensitivity.

Carbamates are frequently used for agriculture and residential insect control. They also have minimal bioaccumulation and environmental persistence. They are less toxic to fish than organophosphates, but still can cause chronic toxicity if overused around an aquasystem (Fulton et al., 2013).

Pyrethroids and nicotinoids are also commonly used in the environment. Nicotinoids cause irreversible block of the post synaptic nicotinoid receptors. Pyrethroids cause damage to the sodium channel in the neurons leading to hyperexcitability, tremors, ataxia and paralysis (Sabra and Mehana, 2015).

There are many other types of insecticides to consider. Although most will not persist in the environment more than one or two weeks, if used consistently, they may lead to chronic disease. This may appear as decreased growth, low reproduction, and slow increase in mortality.