Fish Disease Symptoms Aren’t Always What They Seem

It’s important to strike a balance between quick intervention and overreaction when it comes to marine fish disease symptomsMost marine aquarium hobbyists keep a close eye on their fish for certain tell-tale signs of ill health. And that’s a good thing, since quick intervention in the case of fish disease can often be the difference between life and death for the specimen(s). On the other hand, we do need to be cautious about overreacting to every suspicious visual or behavioral symptom because sometimes these warning signs may not be what they seem. Remember, if misapplied, medications and therapeutic protocols for fish can do considerably more harm than good. It’s important to have a fairly high degree of confidence in your diagnosis before proceeding with treatment. That means you have to guard against misinterpreting normal behaviors or forgetting that more than one problem can cause similar symptoms.To help illustrate this point, here’s a sampling of symptoms that may or may not spell trouble for your fish depending on the context: Flashing If you’ve ever been through a major outbreak of Cryptocaryon irritans, no doubt the sight of a fish turning on its side and scraping its body on the rockwork causes your heart to skip a beat. And, indeed, flashing is a potentially worrisome symptom. However, this behavior doesn’t automatically signal the presence of a parasite or other problem

Why Isn’t Cryptocaryon irritans a Major Problem for Wild Marine Fish?

Whitecheek Tang (Acanthurus nigricans) afflicted with Cryptocaryon irritansDuring yesterday’s Thanksgiving get-together, which my wife and I host for my side of the family every year, a teenaged nephew asked me about marine ich (Cryptocaryon irritans)—the one fish disease he’s heard something about from a friend who keeps saltwater tanks. As I explained the parasite and its lifecycle and why I think it’s so important to quarantine new specimens, he asked, “If ich spreads so easily, why aren’t all the fish in the ocean infected?” Thrilled that, for once at least, I could offer my curious young nephew something akin to wisdom, I explained that the following factors help keep ich infections at a manageable level in wild fish populations:The vastness of the ocean Even though coral reefs appear to be bristling with fish, the density of the fish population relative to the volume of the ocean is, if you’ll excuse the pun, a mere drop in the bucket. Remember, during the tomite, or theront, stage of the Cryptocaryon lifecycle, the free-swimming parasites must find a host fish to attach to and feed upon within a relatively short period or they die. In the vast ocean, with its limitless water volume and powerful, dynamic currents, only a very small number of tomites ever succeed in locating a host. On the other hand, in a closed aquarium system, even if the actual number of fish specimens is fairly small, the population density is still extremely high relative to the volume of water. Of course, the density of host-seeking parasites relative to the water volume is also very high.