parasite · pond-mostly

Anchor Worm (Lernaea)

Anchor worms (Lernaea) are visible white-green parasites (0.5-1 inch) protruding from fish skin like tiny spaghetti. Common in koi + goldfish. Treatment: Dimilin + manual removal.

Severity: Moderate - visible + uncomfortable but treatable

Symptoms

Visible white/green worm-like protrusions on fish
Inflammation at attachment site
Fish scratching against objects
Secondary bacterial infection at bite sites

Cause

Lernaea parasites attach to skin + burrow embedded "anchor". Common in pond fish.

Treatment

Always treat in a separate quarantine tank. Most medications are toxic to coral, invertebrates, and live rock biology.

Diflubenzuron (Dimilin). Single pond-wide treatment kills all life stages. Most effective for outbreaks.

Manual removal. Net fish, grasp anchor worm with tweezers, pull straight out + dab iodine on wound. For small infestations.

Potassium permanganate. Bath treatment kills external parasites. Repeat 7 days later for hatching cycle.

Prevention

Quarantine new pond fish 21-30 days. Treat prophylactically with Dimilin in spring.

Browse the full disease database for 45 aquarium conditions with treatment protocols, or check the care library for prevention-focused husbandry guides. Use our symptom matcher to rank likely diseases from observed signs, the water parameter checker to diagnose related water-quality issues, or the QT timeline calculator to plan a treatment schedule.

Aquarium-keeping fundamentals

Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.

Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.

Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.

Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.

Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.

Frequently asked questions

How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.

What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.

How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.

Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.