What are the factors affecting the efficacy of fishery drugs?
1. Dosage and dosage form of the drug
The effect of a drug varies with the dosage, and may even change qualitatively. For example, when the astringent metal drug zinc sulfate is used topically, a low concentration has an astringent effect, a medium concentration has an irritant effect, and a high concentration has a corrosive effect. Different dosage forms of a drug, even when the drug dosage is the same, also differ in the strength, effect and duration of action.
2. Route of administration
The route of administration, time of administration, number of administrations and repeated medication can all affect the effect of a drug. External routes of administration such as medicated bath (or spraying all over) differ markedly from routes such as oral administration (or injection) in drug action; with different administration times (day or night), even if the dosage used is the same, the effect will also differ.
3. Animal state
Different conditions and physiological states of aquatic animals themselves produce different drug effects. (1) Species differences: different species and strains of aquatic animals, or different individuals of the same strain, differ in sensitivity to drugs; (2) Physiological differences: generally, young and old aquatic animals are more sensitive to drugs; (3) Individual differences: different individuals have different tolerance to drugs, which may be related to individual genetic factors; (4) Functional and pathological condition of the body: generally, thin, malnourished aquatic animals and those under pathological conditions are more sensitive to drugs.
4. Environmental factors
For aquatic animals, the environment has a greater influence on drug action. The main influencing factors are: (1) Water temperature: drug efficacy is generally positively correlated with water temperature, but some drugs are the opposite; (2) Organic matter: it affects the efficacy of most drugs, such as potassium permanganate, chlorine-containing disinfectants, etc.; (3) pH: acidic drugs, anionic surfactants and antibacterial drugs such as tetracyclines have weakened action in alkaline water, while alkaline drugs, sulfonamide drugs and cationic surfactants, etc., have enhanced efficacy as pH rises; (4) Dissolved oxygen: when dissolved oxygen is higher, aquatic animals have enhanced tolerance to drugs, while when dissolved oxygen is lower, poisoning is more likely to occur; (5) Light and season: aquatic animals have a stronger tolerance to drugs at night than during the day, and are more sensitive to drugs in summer than in winter; (6) State and resistance of pathogens: some parasites that can form cysts often form cysts under the stimulation of drugs, and their resistance to drugs is then markedly strengthened; in addition, stress factors such as fishing, transport and water changes can also increase the sensitivity of aquatic animals to drugs.