NEMATODES IN FISH

kelolalaut.com - Nematodes, or roundworms, infect many different species of aquaculture and wild fish. What are the common nematodes in fish?

1. CAMALLANUS

Target Tissues: Intestinal tract; all other organs

Appearance: Smooth, cylindrical, elongated, reddish thread-like worm

Size: Up to 1 cm in length

Movement: Free-moving; serpentine (snake-like) movement

Note: Often protrudes from anus; live-bearer; larvae may be seen in adult; indirect life cycle (requires intermediate invertebrate host)

2. CAPILLARIA

Target Tissues: Gastrointestinal tract

Appearance: Smooth, elongated, worm; double-operculated barrel-shaped eggs may be seen in females; may see eggs only in fish tissues

Size: Males approx. 5.4–7.4 mm; gravid females approx. 9.4–16.5 mm

Movement: Free-moving; serpentine (snake-like) movement

Note: Direct life cycle; can spread directly from fish to fish

3. CONTRACAECUM

Target Tissues: Body cavity, liver, muscle, heart, swim bladder

Appearance: Grossly visible; often seen coiled (encysted)

Size: Larvae (found in fish) up to approx. 20 mm in length

Movement: Movement usually not seen in fish

Note: Indirect life cycle includes birds and invertebrates

4. EUSTRONGYLIDES

Target Tissues: Internal tissues

Appearance: Grossly visible; coiled, reddish worm (encysted)

Size: Larvae (found in fish) 11–83 mm in length

Movement: Movement usually not seen in fish

Note: Fish is intermediate host; definitive host is wading bird; oligochaete worm required as intermediate host in some species

In aquaculture situations, fish become infected with nematodes if they are fed live foods containing infective life stages or if they are raised in culture settings that promote the growth of other animals that carry the infective stages of the nematode (vector or paratenic host) or allow nematodes to complete their life cycle (intermediate hosts). Some nematodes can be transmitted directly from fish to fish. Adult nematodes are typically found in fish digestive tracts.

Small numbers of nematodes may be present in fish without causing significant symptoms. In more severely infected fish, evidence of disease can include emaciation (wasting or significant loss of body mass), nodules or masses present in skin or muscle, stunted growth, abnormal swimming, lethargy, or death. Adult nematodes in the digestive tract can deprive fish of nutrients causing the fish to waste. Nematodes use hosts to complete their life stages. When fish are infected with adult reproductive nematodes, they are known as the definitive host of that nematode species.