Never read the entire article, missed the Malawi reference. lol Yes, very true what you say, Lake Malawi is not nearly the liquid rock that many authors state.
As far as HITH, it is caused by stress, so determining what the stress trigger is in each set up is typically near impossible - unless all other factors are equal, including the individual immune response of each individual fish, which of course can vary as well. For many years researchers in this field believed that overall poor husbandry, which leads to stress & immunosuppression in many species of fish was the leading cause of HITH disease. (Becker 1977, Goldstein 1979, Bassleer 1983, Andrews et al. 1988, Ferguson 1989, Vickerman 1990)
If one follows the more current research, most researchers also now believe that the parasite that causes the holes are S. vortens, in which there are two main forms - intestinal (aka Malawi bloat) and histozoic (systemic) infections, with HITH being a result of the latter form.
We also now know that the parasites that cause HITH prosper under certain water parameters. (at least under lab conditions)
Ironically at elevated pH levels, this parasite doesn't fair so well.
http://www.ncbi.nlm.nih.gov/pubmed/10715818
In vitro studies on optimal requirements for the growth of Spironucleus vortens, an intestinal parasite of the freshwater angelfish.
Sangmaneedet S1,
Smith SA.
Author information
- 1Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
Abstract
Spironucleus vortens were cultivated in either an artificial medium at different temperatures, or in medium at various pH conditions or supplemented with different bile concentrations at 25 degrees C. Temperature, pH and bile requirements for the optimal growth of the parasite were determined. Parasites multiplied quickly at 28 and 31 degrees C and reached maximum numbers on Day 4 of cultivation, whereafter they did not survive. At 25 degrees C, parasites survived longer than those at 28 and 31 degrees C with no difference in multiplication rate during the exponential phase. The longest survival period was seen at 22 degrees C, although the growth rate of the parasite was not as high as those at 25 degrees C. At a higher temperature of 37 degrees C, no parasites were observed alive after the second day of cultivation. Optimal pH range for the parasite's growth was 6.5 to 7.5, with the highest cell number at pH 7.5. Parasites survived longest (15 d) at pH 6.0, although the maximum number of cells was lower than those at the optimal pH. Parasites were dead within 24 h at pH levels above 8.5 or below 5.5. All cultures supplemented with either bovine or fish bile yielded numbers of parasites lower than cultures with no bile. In addition, parasite growth was significantly suppressed in medium supplemented with higher concentrations of bile. These results indicate that the optimal condition for the in vitro cultivation of S. vortens is 25 degrees C and pH 6.5 to 7.5 without supplementation with bile.
................................................................
There is also evidence that demonstrates what may start as a case of intestinal infection, can end up resulting in a systemic infection in some fish. And one of the best reads on this subject is one that I have linked to numerous times over the years.
https://theses.lib.vt.edu/theses/available/etd-120399-140825/unrestricted/ANGEL.PDF
If one wants to totally eliminate the possibility of HITH, all one needs to do is to fully understand, and then eliminate the pathogen that causes it. Unfortunately just like Lake Malawi being liquid rock (which it is not), there is much misinformation on the subject of HITH.
