I have a grasscarp with one very protruding eye. it is not cloudy, but on looking a bit closer it seems that there is fluid behind the top layer over the eye. he is fine in himself. Any ideas please.

Dawn

This sounds like the start of a bacterial infection. If you have access, you should consider either Tricide NEo dipping, PLUS medicated food, I am partial to MediKoi. It's better made without top dressing or super heating. Checking your water quality is a good first step because high nitrates are a common cause of chronic illness among Goldfish, crowding is another. One inch of fish per ten gallons is a good rule of thumb, more on tjat is at KoiSchool.com

No matter what you ultimately do about this condition, please, FIRST, check your water for Ammonia, Nitrite, and Nitrate. To learn more about these several important water quality parameters, please see this link. Establish that the Ph is higher than 7.0 using any of the many great test kits available. To raise pH you could use Baking Soda for the "quick fix" and then follow it up with a buffer. Make sure, too, that you have seen KoiCrisis.com - You can click on the fish there to get specific information about treatments and options.

Want a shotgun remedy for use on parasites and bacteria once you've ruled out crowding, poor water, high nitrogen or low pH?

Here's a perfect shotgun remedy that won't hurt fish:

(1) Salt to 0.3 or 0.6%
(2) Warm the fish no faster than one degree per hour, up to the mid seventies, or if you want to combat Koi Herpes Virus, use the same "one degree per hour" heating from their ambient temperature up to 86°F
(3) MediKoi food is, in my estimation, by far the best made, best formulated medicated food. It will help control bacterial infections.
(4) Dimilin handily controls comparatively rare but large parasites like Anchor Worms and Fish Lice.
(5) Prazi or Prazi containing medications controlf Flukes on Koi and Goldfish best.

Using all of the above at the same time can be highly successful against most parasitisms and infections. The space in which this is done should be the largest possible (100+ gallons), with plenty of hiding-cover, algae or live plants, and plenty of wter turnover for aeration. This protocol could be hampered when applied to salt-resistant Costia. A Formalin treatment on the way into the quarantine where the above will be applied will break the lifecycle of Costia and prevent it emerging in the quarantine tank.

Thank you for your consideration.

Dr. Erik Johnson