When choosing fish in a store, pay attention to their activity and appearance. Healthy individuals should be active, with clean fins showing no signs of plaque, erosion, or damage. Avoid specimens with clamped fins, an unnaturally bloated abdomen, or, conversely, severe emaciation, as this may indicate the presence of parasites or chronic diseases. — Examine the scales: they should lie flat against the body, without visible sores, spots, or signs of fungal infection. — Check their behavior: fish should show interest in their surroundings, and not stay aloof, at the water surface, or on the bottom in a lethargic state. — Make sure there are no dead fish in the platy tank, as this indicates unfavorable keeping conditions or an infection in the system.