Hello, I have an aquarium of bottom dwellers among them a chocolate cat and a spotted desert cat and moderate weather. Yesterday morning the spotted desert cat swelled drastically and his stomach turned red and my breathing was heavy and he had not eaten since yesterday. Would appreciate help! Details about the aquarium: My fish live in a 150 liter /40 gallons tank aquarium, water changes once every two to three weeks. Eat dry food, the fish I have around 6 years old and have never fought before or hurt each other. Last water change was done a week ago.