COMMON FRESHWATER FISH DISEASES By Peach Reid When examining common freshwater fish diseases, we must look at three important factors-identification, cure and also cause. As the old saying goes, "An ounce of prevention is worth a pound of cure." One of the most common problems is "ich" (ichthyoptherius), which appears as tiny white spots covering the entire fish body. All types of fish can contract ich, but certain kinds-clown loaches, Pimelodella pictus (angellicus), hatchetfish and (wild-caught) silver dollars, for example-are more prone to breaking out with it. Ich occurs mostly during times of the year when there are seasonal temperature differences. Rapid temperature change, pH fluctuation and increase in ammonia are the leading causes of ich. The preferred method of treatment to kill this parasite is malachite green. Scaleless fish can only tolerate one-half of the recommended dosage. Warm water temperature and at least one teaspoon of salt per gallon of water increase the effectiveness of malachite green treatment. Another common problem is "tail rot." The symptom is described by the name a deterioration of the tail. Though other fish can suffer from tail rot, it is seen most often on livebearers (platies, variatus, swords and guppies). Gen7 erally, tail rot is brought on by high ammonia and/or high bacterial levels. Treatment can be effective with any broad-spectrum antibiotic; we use Kanamycin and Nitrofurazone. Livebearers are also prone to columnaris. Fancy guppies and sailfin mollies are especially vulnerable to those grayand-white lesions on the mouth and/or caudal area, and to fin deterioration in general. Overcrowding and poor filtration, which can result in high ammonia and bacterial levels, are the leading causes of this condition. Any broadspectrum antibiotic can be effective against columnaris, as with tail rot, because both are bacterial diseases. Again, we use a Kanamycin and Nitrofurazone combination. The last disease we'll look at this month goes by the name of "shimmies." Like tail rot, the name describes the symptomatology. Gouramies and sailfin mollies are the most likely to manifest this back-and-forth rocking motion. The conditions that cause it are change in temperature and poor water quality. The combination of malachite and formaldehyde is the most effective cure we have found. When starting a treatment program, it is important to keep several things in mind: - Different products may contain varying amounts of the active ingredient.   Follow instructions on the package carefully. - Make sure the treatment program is continued for the entire prescribed   length of time. - Do not add new fish to the treated tank or sell any fish being medicated. - Keep one teaspoon of salt per gallon in the water. - Monitor ammonia levels (keeping them at zero). A review of the causal factors in all these diseases - overcrowding, poor filtration, high ammonia levels and rapid temperature and/or pH changes - reveals a common link: All relate to water quality. To keep freshwater fish healthy, proper biological and mechanical filtration are mandatory. Controls for maintaining steady temperature and pH are also necessary. Good central systems address all these requirements. However it is done, good management of all these factors results in the reduction of stress, and reduction of stress is the primary factor in the prevention of disease. Peach Reid is president and Co-owner of Fish Mart Inc., a West Haven, Conn., livestock wholesaler.