Fish Health (Cont.)
Shimmies describes abnormal swimming behavior of many species of livebearers, including guppies (Poecilia reticulata), mollies (Poecilia sphenops, Poecilia velifera, Poecilia latipinna), swordtails (Xiphophorus hellerii), platies (Xiphophorus maculatus), and variatus (Xiphophorus variatus).
The predominant cause of shimmies in livebearers is a water chemistry that is too soft and acidic. Mollies are the most common fish to exhibit the shimmies symptom as they like very hard and alkaline water. Increase water hardness as outlined in this book to 300 to 600 ppm (17° to 34° dGH) and increase alkalinity (pH) to 90 to 160 ppm (5° dKH to 9° dKH). pH will be affected negatively by any nitrate in the water. The higher the nitrate concentration the lower the pH. Maintaining a pH of 7.6 to 8.3 is recommended for most livebearers and for mollies a minimum of 7.8 is recommended.
Hole in the head describes a symptom (not a disease) that can develop in fish in the aquarium due to poor water quality. Hole in the head only occurs in aquarium kept fish, it is not found in wild fish populations. Marine hobbyist have a similar condition to hole in the head, but it is commonly referred to as head and lateral line erosion (HLLE). The symptom looks like pits in the head or receding skin on the head and sometimes the lateral line. In freshwater the Hole in the head symptom is most commonly seen in large cichilds, including oscars (Astronotus ocellatus), and discus (Symphysodon sp.).
A classic example of hole in the head symptom in this jaguar cichlid (Parachromis managuense).