Water quality was dismissed as a likely cause of the problem. Good water quality was maintained by a combination of use of sand filters, ozone, and periodic water exchanges with saltwater mixed from Instant Ocean sea salt. We do not use activated carbon. Normal nitrate levels were maintained in the range of 15 to 20 milligrams per liter ,(mg/l), Nitrate Nitrogen , (N03-N). pH averaged 8.25 and salinity was 32 parts per thousand, or a specific gravity of 1.023. At the onset of the HLLE, salinity was dropped to inhibit parasite reproduction, in case this was the cause. The erosion continued and salinity was eventually brought back up to 1.023.

In reviewing other possible causes for theis malady we next focused on possible dietary deficiencies, because no obvious pathogens were found. Our fish were receiving a varied diet including romaine lettuce and spinach. Initially we tried elevating the level of vitamin C by incorporating a supplement into a gelatin based food, but this had no effect. We next considered supplementing the level of vitamin A. According to the Applied Nutrition and Diet Therapy, page 852, "One of the most important functions of vitamin A is to maintain the integrity of the epithelial cells....As a result, surfaces of the skin and membranes lining all passages that open to the exterior of the body, as well as glands and their ducts, are susceptible to disease." This was the basis for trying increased amounts of vitamin A after the vitamin C supplement by itself failed to produce results. It was our feeling that the laining of the lateral line ducts had deteriorated.

We were concerned with the possible toxicity of high vitamin A levels that has been reported for certain animals. Upon reviewing the nutritional value of different types of lettuce, we found them to be very low in nutrients and began researching the nutritional value of other green vegetables. Spinach appeared to be higher than lettuce, but it does not hold up well in sea water. Carrots were found to be a good natural food, but they had to be shredded and were quite messy to feed. Still, we fed carrots solely for six to eight weeks and observed a resolution of the HLLE. A more complete literature review made broccoli an obvious choice. It is well balanced in many vitamins in addition to the high level of vitamin A, and also has other features that make it acceptable. It holds up very well in the aquarium. Many fish like the flowerettes when they are first added. Only the larger fish could break open the woody layer on the stalks, but once opened small fish feed on the softer pulp material. We replaced the carrots with broccoli, and we are currently using it as a well-balanced maintenance diet.

After replacing the lettuce diet with first carrots and then fresh broccoli, the HLLE improved to the extent that only a few scars remained on the most severely affected fish. After nearly eight years in the exhibit, most of the original batch of blue tangs are still alive. Broccoli, supplemented with peas and other prepared foods, dominates the diet. No HLLE sypmtoms are evident in any of the fish in the exhibit.

Reference: Burtis, G,J. Davis, and S Martin. 1998 Applied Nutrition and Diet Therapy. W. B. Saunders Co.