Cryptocaryon (Marine white spot)

Figure 9: Cryptocarypon irritans,exflagellate form

This ciliated parasite shown in figure 9 resembles Ichthyopthirius mulitifilis, the cause of white spot in freshwater fish. The life cycle is similar to I. Multifilis. The parasite can be seen to be pear shaped, but has a 4 lobed nucleus instead of the horseshoe shape of the freshwater parasite. The infective stage aggressively burrows into the fish, causing it to flash and flick against objects in the tank. The fish may even swallow sand as they attempt to relieve the infection. The most obvious symptom is however the white spots.

Treatment is via Paracide, which contains copper and formaldehyde. Copper is lethal to invertebrates, so fish in reef systems must be treated in a hospital tank. The infective stage can only last 48 hours in the absence of a host. Reef systems can be treated with Bactocide at 1/2 dose. This will not harm invertebrates, but it has been known to make them look dull for around one day.

An alternative treatment is hyposalinity. A dip in a bath of 16 parts per thousand salinity will kill the infective stages, thus fish only systems, can be purged of Cryptocaryon infective stages by temporarily lowering the salinity. 

.Ichthyobodo necatrix (formerly Costia necatrix)

This is one of the smallest parasites commonly encountered in freshwater fish, and is best viewed at 400X. It can be seen to be a comma shaped parasite, and usually occurs either attached to an epithelial surface, or swimming by frantic beating of hair-like projections from one end, called flagella. Symptoms of infection include excess mucous production, respiratory distress, and general debilitation, as the parasites feed on the gill and skin cells. Treatment is via antiparasitics such as Malachite green and Formaldehyde. Use FMG Mixture for Koi, Eradick / White Spot for more sensitive species and pondfish. Use Ichcide or Aquarium White Spot in freshwater aquaria. Icthyobodo is not believed to infect marine fish.

An alternative is to dip the fish in a salt bath of up to 3 Oz per gallon for 6 - 10 minutes. For smaller fish use 1 1/2 Oz salt per gallon for 30 minutes. After the salt bath it can be beneficial to place the fish in strong running water to wash of the excess mucus produced by the salt.

NB: Some strains of Ichthyobodo are known to be resistant to salt treatment. Thus if this cure is used, check its affectivity by performing regular mucous biopsies on the fish to monitor re-infection.

Heteropolaria (AKA Epistylis)

Figure 11: Heteropolaria Sp.

These parasites are called sessile peritrichs, and are found in freshwater fish. Shown in figure 11 they can be seen to be a large body rooted to the epidermis by a stalk (hence `sessile'). They are very numerous in water with a high level of organic matter. If a fish becomes stressed, its immunity to these parasites declines and they invade the fish leading to white-grey patches, and red sores in heavy infections. Interestingly, the parasite only uses the fish for attachment; it does not feed on the host, so it is not a true parasite. However through the attachment, wounding is created and secondary bacterial and fungal infection often follows. Treatment can be through salt baths as in Icthyobodo above, or antiparasitics. Use FMG mixture for Koi, Eradick / White Spot for more sensitive fish and pond fish, Use Ichcide or Aquarium White spot in freshwater aquaria.

Prevention is the best policy by maintaining good pond or tank cleanliness. 

Oodinium and Amyloodinium

These are Dinoflagellate parasites (Flagella are long hair-like structures the cell uses for propulsion), which contain the green photosynthetic pigment chlorophyll. In freshwater fish, Oodinium causes velvet disease, where the fish appears to be covered in gold coloured dust, which can be enhanced by shining light on the fish in a darkened room. In marine fish the closely related Amyloodinium causes Velvet disease or Coral Fish Disease, whose appearance is the same as above.

The parasite is flagellated in the free-swimming stage, but once attached to the fish it loses the flagella. (Figure 12).

The parasite can be recognized as it has a pigmented body inside the cell, which gives it a slight green colour. In both freshwater and marine fish, the parasite attaches to the skin and gill epithelium. Root like attachment organs called rhiziods penetrate deep into the fish, causing severe pathology. Symptoms include distressed breathing in gill infections, flashing, scratching, and skin infection. Secondary bacterial infection is common.

Figure 12: Oodinium Sp. exflagellate form.

Both Amyloodinium and Oodinium are best treated using a copper-based medication such as Paracide. Marine fish should be treated in the absence of invertebrates, as these are very intolerant of copper, and freshwater snails will also be killed by the treatment.

An alternative to the copper-based treatment is Bactocide. This can be used in marine aquaria at half the dose of that applied to freshwater systems. The treatment will not harm marine invertebrates, but has been known to make them look dull for around one day.

These parasites are notoriously difficult to treat, as the parasite forms a resistant cystic structure in the substrate of the aquarium, and this can lie dormant, reappear and then cause relapses of infection.