Dropsy describes a fish whose body is filling with fluid faster than it can clear it. Vets are careful with the word, because it names a sign, not a single illness: the fluid build-up is the visible end of an internal failure, most often involving the organs that regulate the fish's water balance, and it can follow bacterial infection or organ damage. Understanding that distinction shapes how you read the signs — you are looking at evidence of something seriously wrong inside, not at a surface problem.
The pinecone sign
The hallmark is best seen from above. As fluid accumulates under the skin, the scales are pushed outward and begin to lift away from the body, each one standing at an angle until the fish's outline resembles a pinecone. From the side you notice the swelling first — a belly that rounds out more each day, sometimes unevenly — but the top view is the confirming angle, and it is worth training yourself to look at your fish from above regularly for exactly this reason. Once scales are visibly raised, the fluid build-up is already advanced.
The signs that travel with it
Swelling rarely arrives alone. The eyes may bulge outward as pressure builds behind them. Gills can look pale, the fish grows lethargic and spends its time resting on the bottom or hanging motionless, and appetite fades, then stops. Stringy, pale waste, a reddened vent, or small ulcers and red patches on the skin can appear in some cases. Behaviour often changes before the body does: a fish that was first to the surface at feeding time starting to hold back is an early whisper of the problem that the pinecone stage later shouts.
Why it should not be watched and waited on
With many fish complaints, a day of clean water and observation is a reasonable first move. Dropsy is the exception keepers learn to treat differently: because the visible swelling means internal systems are already failing, the window in which intervention can change the outcome is short, and it closes while you wait. A fish showing raised scales and swelling belongs in front of an aquatic veterinarian or experienced fish health specialist the same day, isolated in a hospital tank if you have one so it can rest away from tank mates while you arrange that help.
Giving the specialist something to work with
What turns a worried phone call into useful triage is a timeline: when you first saw swelling, when the scales lifted, what the water tests read that week, what changed in the tank recently — new fish, a filter problem, a missed run of water changes. Write those observations down as you notice them, with dates, in the fish's Pet Passport on KinsLe, and you hand the vet a case history instead of a guess; whatever the underlying cause turns out to be, that record also protects the remaining fish, because it anchors when the problem began relative to everything else in the tank.