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Selecting Healthy
Fish Basics
Assuming you can choose a fish that is compatible with the ones you already have, here's the skinny on what to look for to select a fish that is healthy.
First off, fish don't disguise illness or malaise well at all. If there is something wrong, there will usually be outward symptoms. Granted many of these symptoms apply to more than one malady and fish often suffer the effects of different diseases at the same time, but what you need to know is what to look for to avoid trouble in the first place. First off, a healthy fish is active and swimming, unless it’s a species that rests motionless unless feeding like many oddball fish and catfish do. Their colors should be bright, clear and intense. They eyes should also be clear, and of normal size. A bulging eye or one with a bubble of trapped air visible is usually a symptom of a serious underlying disease. The same can be said of tiny bubbles trapped in the tissue of the fins.
The gills should be bright pink, but not red or appear inflamed. While many fish take a quick dash to the surface for a gulp of air (as many catfish do), hanging below the surface and gasping for breath is a sign of impending doom. It is usually an indicator of hypoxia (insufficient oxygen supply) and stress. A fish in this condition is very vulnerable to disease outbreak. The fish’s body should be sleek and devoid of bulges. The abdomen should look full, but not distended. Sunken bellies, eyes, and depressions on the top of the head between the eyes and the dorsal fin are sure signs of starvation and a weakened state. The aforementioned area of the head is where the majority of the limited amount of fat fish can store is deposited. If this area is depressed, the fish hasn’t eaten in quite some time. Fish that are regularly fed associate a person’s presence near the tank with getting to eat and in that case, get quite excited in anticipation of being fed. They often will follow your hand if you graze it across the upper rim of the aquarium.
The fins should be undamaged, smooth around the edges, and clear with no cottony or cauliflower-like growths. Visible streaks of deep red are also something to be avoided as it is a symptom of a type of blood poisoning associated with an internal bacterial infection. Fish varieties with elongate fins (like bettas, veiled angelfish and goldfish) often have uneven or jagged edges to the fins, but this is not necessarily an indicator of disease. In large fancy goldfish varieties with white or translucent tails, it is common to be able to see the blood vessels in the tail. They should appear a soft red to pink color. If they are very visible with a deep red color and appear inflamed or numerous, the fish should be avoided. If you are unsure, observe the fish over several days before purchasing. If the reddening deepens after a few days and the tail starts to have a turbid appearance (slightly cloudy), take a rain check.
Scales should be shiny and have a reflective quality. Some fish have muted colors for camouflage, but the scales should still appear clear and not protrude. Fish that have a pine-cone like appearance to the body are suffering from a bacterial infection (often referred to as “dropsy”) and should be avoided. This malady is almost always fatal. By the time the symptoms manifest on the outer region of the body, the damage done to the inside is severe. If the overall body looks dull or there are cloudy or slimy patches on the skin, this is usually a symptom of a protozoan infestation (usually a species of Costia). Rounded white or yellow specks are also a sign of trouble, indicating an infestation of ick, velvet, or Oodinium. Fish with ulcerations (a wound or injury on the skin or mucous membrane accompanied by dead or dying tissue) should also be avoided. The cause of ulcerations can range from physical injury to damage by a parasite (like anchor worms or fish lice). Either way, the fish’s immune system is severely compromised and it should be avoided.
Another part of the body to check over is the barbel area (on catfish and characins). They should be in tact and show no signs of redness, inflammation or damage. If the barbels are streaked with red or have red blotches, it is a sign of being kept in poor water quality. Ammonia literally burns the highly sensitive barbells and is a likely culprit of a reddened condition.