Great diving beetle

The great diving beetle (Dytiscus circumflexus) belongs to the order Coleoptera and the family Dytiscidae. This large aquatic predator represents a significant threat within fish farming and hatcheries, as its predatory habits can severely impact the success and productivity of aquaculture systems by consuming juvenile fish.

This pest prefers stagnant or slow-moving water bodies. Both adults and larvae are voracious predators. In an agricultural context, their presence is detrimental to nursery ponds specifically designed for breeding fry, where they can decimate a large percentage of the stock within a very short period.

The life cycle undergoes complete metamorphosis, consisting of egg, larva, pupa, and imago stages. Females lay their eggs within the tissues of aquatic plants. The larvae, often called "water tigers," possess sickle-shaped mandibles used to inject digestive enzymes into their prey, allowing them to consume soft tissues rapidly.

The damage caused is primarily the physical destruction of fish fry, tadpoles, and other beneficial aquatic organisms. A population boom of these beetles leads to a sharp decline in survival rates of young fish, resulting in substantial economic losses for fish farming enterprises and reducing overall farm profitability.

Protection strategies include regular maintenance to remove excess vegetation from ponds, which serves as an egg-laying site, and the draining of pond beds during winter to eliminate overwintering populations. Additionally, using fine-mesh filters when filling ponds is an effective preventative measure to stop adult beetles from migrating into areas where young fish are being raised.