Why do soft water fish die in hard water?

[Rod]

In my experience...soft water don't last long in hard water

Why?

Do their kidneys pack it in or is it simply bacteria ( good & bad) love alkaline water and this gets them

What's the science?

 

[gerald]

I've been looking for info on this question for a long time too. Some species have trouble in hard water and some dont. Neon tetras can live just as long (3-4+ years) in moderately hard water as in soft water. Soft-water fish gills and kidneys are very good at extracting and retaining minerals (Ca, Mg, and others) from their surrounding water at very low ambient concentrations, based on studies with neon tetras, pacu, banded sunfish and others. My best guess based on a synthesis of bits and pieces I've read from various sources is that some species can regulate their ion uptake cells better than others, reducing uptake when minerals are abundant. Those that cannot regulate their ion uptake as well (obligate soft-water species) probably end up with ionic imbalance in their blood and cell fluids. And yes the lower prevalence of bacteria and disease bugs in soft/acidic water may be another factor.

... and then of course there's the issues & debates about spawning, fertilization and egg development and how/why/if they are affected by pH and ion concentrations.

Here's a few articles if you can get access to them. There may be newer studies too. Google "fish osmoregulation ion-poor black water" or some similar combination of words and see what's out there. If you find any good info, please post here.


Physiol Biochem Zool. 2002 Jan-Feb;75(1):37-47. Diverse strategies for ion regulation in fish collected from the ion-poor, acidic Rio Negro. Gonzalez RJ, Wilson RW, Wood CM, Patrick ML, Val AL. Laboratory of Ecology and Molecular Evolution, National Institute for Amazon Research, Alameda Cosme Ferreira, 1756. 69.083-000 Manaus, Amazonas, Brazil. [email protected]

Physiol Zool. 1998 Jan-Feb;71(1):15-22. Effects of water pH and calcium concentration on ion balance in fish of the Rio Negro, Amazon. Gonzalez RJ, Wood CM, Wilson RW, Patrick ML, Bergman HL, Narahara A, Val AL. Department of Aquaculture, National Institute for Amazon Research, Manaus Amazonas, Brazil. [email protected]

Physiol Biochem Zool. 1999 Mar-Apr;72(2):156-63. Ionoregulatory specializations for exceptional tolerance of ion-poor, acidic waters in the neon tetra (Paracheirodon innesi). Gonzalez RJ, Preest MR. Department of Biology, University of San Diego, 5998 Alcalá Park, San Diego, California 92110. [email protected]