A Brief Introduction to the Effect of Mannich Base Ingredient in Killing Fish Parasites

Mannich base ingredient is a highly efficient biological insecticide extracted from the roots and leaves of the pure plant eucalyptus and made through scientific processing. More than 1000 years ago, people already knew that eucalyptus has medicinal value. Especially in rural areas of southwest China, its roots and leaves are commonly soaked into a liquid to directly kill maggots and other pests. In recent years, after in-depth research by relevant departments at home and abroad, preparations have been extracted from it, and it is recognized as a biological insecticide that is broad-spectrum, highly efficient, low-toxicity, easily degradable, residue-free, free of "three-causing" effects, and free of drug resistance. We have applied it to kill fish Dactylogyrus, ciliates, and other parasites, and achieved relatively ideal results. It is briefly introduced below for reference.

According to analysis, the main active ingredients of this product are Mannich base ingredient (1.8-cineole), 2-pinene, camphene (L-campnere and Cinnamomnncamphora, etc.), among which Mannich base ingredient has a prominent effect, and its effect is even more significant when combined with aromatic ring side chains and long-chain aliphatic substances. At a concentration of 0.005 mg/L, it can kill Gyrodactylus and Dactylogyrus within 1 hour.

Mannich base ingredient has particularly strong permeability and is a highly permeable substance. It can effectively penetrate the chitin and gelatinous membrane on the body surface of insects, causing functional disorders and atrophy of the insect body, thereby destroying enzyme activity in the insect body. Tests show that it is very effective in killing Ichthyophthirius multifiliis populations carrying cyst bodies. In addition, this product contains a substance with peroxide properties, which can produce free radicals that are relatively sensitive to helminths, causing deformation, atrophy, and death of the insect body, yet it is harmless to fish, shrimp, livestock, poultry, humans, and others. The famous American toxicologist Professor Fick once used the model C=Coe-KT equation to calculate and confirm that it has a rapid lethal rate against insect bodies.

I. Test Materials and Methods

1. Drug stability determination. The trial drug was tested after 1, 3, 6, and 18 months of sealed storage at room temperature. The determination method used rapid thin-layer chromatography (TLC) with standard sample spotting. Organic solvents were used for development and colorimetric determination. The results showed that the active ingredient contents were 2%, 5%, and 7%, respectively, indicating that its properties are stable. After 18 months of storage, it reached the product's specified standard.

2. Insect-killing test. The practical material was crystallized Mannich base ingredient with an extracted effective content of 8%. The experimental European eel and American eel seedlings (microscopic examination showed an average of 7 parasites per gill filament) were obtained from two eel farms in Fuqing and Hefei. Each experimental container held 50 kg of water, with parallel concentrations set at 0.05, 0.1, 0.3, 0.4, and 0.5 mg/L, and a full microscopic examination was performed every two hours, with continuous observation for 120 hours. The results showed that after 24 hours the insect-killing rate reached 60%, and after 60 hours the lethal rate was above 90%. Then, in an experiment on flowing-water eel culture in cement ponds, the drug was applied twice daily. Once in the morning, and in the afternoon after draining water, a supplementary amount of 60% was added to reach 0.4 mg/L. After 72 hours, the lethal rate against insect bodies was 95%-100%. In tests in multiple polyculture ponds totaling more than 1500 mu, it was shown that using a concentration of 0.05-0.1 mg/L to kill Dactylogyrus, Trichodina, and others achieved a cure rate of 95%-100%.

3. Fish behavioral response and safe concentration determination. Eel seedlings were selected as material, and a fish avoidance trough was used to separately determine the behavioral response to 0.2 mg/L, 0.4 mg/L, and a control group. The test results showed that the three concentrations had no effect at all on the behavior of eel seedlings. In addition, we also used the fish safe concentration evaluation method proposed by American scholar Reineye, that is, selecting 120 sq m cement ponds with an average water depth of 1 m, and separately using this agent at 0.4-0.5 mg/L for parallel tests. After continuous observation for 10 days, compared with the control ponds, it showed no adverse effects at all on their feeding or swimming.

4. "Three-causing" determination. The animal isolated hepatocyte sister chromatid exchange (SCE) method was used to compare this product at 0.2 mg/L, 0.4 mg/L, and a control group. The results showed that no induction of chromosomal DNA damage or mutation in cells, or increase in in vivo SCE, was observed, thereby confirming that this product has no "three-causing" effects (teratogenicity, carcinogenicity, mutagenicity).

II. Preliminary Evaluation

In 2006, parasitic diseases caused by fish ciliates commonly occurred in major aquaculture regions across the country, and conventional drugs had already caused these parasites to develop severe drug resistance. The main body of Mannich base ingredient has led to the development of four specialized drugs for killing parasites, such as those specially used for Japanese eel, European eel, and American eel, and those specially used in shrimp-crab polyculture ponds for grass carp, silver carp, crucian carp, bream, and other farmed fish.