Hyposalinity Question

[rkl303]

Hey Dr. Ron this is my first time to your forum but it says your an expert on invertabrates and I thought I might ask my question here.

Anyways I was wondering why exactly hyposalinity kills ich? Is it because there is some special organ in ich that requires salinity at a certain level and not other animals? Or is it because other animals have developed organs that help them tolerate fluctuations in salinity? Is this organ or issue only found in invertabrates?

Basically I am wondering all of this because I am wondering if there is another way to treat for hydroids. I am thinking of trying to keep dwarf seahorses and I keep on reading that hydroids are the very detrimental to dwarf seahorses and was wondering if there were other ways of treating for hydroids instead of very high heated water or panacur(or hydrox).

Oh I guess I should address the question too if hyposalinity has any large effects on bacteria that provides nutrient processing filter on our tanks.

Richard

[MCsaxmaster]

I'll let Dr. Shimek elaborate, but let me offer a few ideas. All aquatic organisms must osmoregulate (that is, control osmosis, the movement of water in and out of their bodies via this process). Most marine invertebrates have body fluids that are equivalent in the number of dissolved species (~have the same salinity) as the water they are in. Many of these animals haven't evolved sophistocated ways control how concentrated or dilute their body fluids are relative to the water they are in. So, for many of them, what's on the outside (in terms of number of ions, not necessarily types of ions) is what's on the inside.

Marine fish show very good osmoregulatory control. Actually, most marine fish have about 1/3 the concentration of ions in their blood as does an equivalent volume of seawater. They must constantly drink water and eliminate salt. The trend is for them to become too salty.

Freshwater fish have the opposite problem. They too have about 1/3 the ion concentration of seawater. Here they tend to lose ions (salts) very quickly and take on too much water. They don't drink and instead produce a lot of very, very dilute urine. They also pump in ions through the gills.

All metabolic processes in all organisms only work within a certain range of environmental parameters. Ionic concentration has a big effect on many processes. If marine fish are kept in low salinity water (for a time), since they are good at controlling the ionic concentration of their bodies relative to the water they are in, their body fluids stay relatively unchanged and they live. For Cryptocarion the range is unlivable. Probably Cryptocarion shows some control over it's body's ionic concentration (it may or may not, I'm not aware either way), but eventually it can no longer 'keep up' and succumbs.

Chris

[rshimek]

Hi Richard,

Chris' answer is pretty much right on. [thanks]

Protozoans, such as the causative agent for marine ich, have a rather limited number of ways in which they can control the ionic balance in their bodies. Once their environment gets outside that range, they die.

Most reef organisms have about the same range of requirements in this regard as they all have evolved in the same environment, but some have developed more or less effective ways of dealing with the environmental changes. In fishes, the waterproof skin and relatively sophisticated excretory organs allow them to persist - for relatively short periods - in extreme environments that would kill many other organisms.

Unfortunately, many hydroids have adapted to estuarine conditions - this means they can withstand quite low salinities, and such a treatment would not affect them at all. Indeed, there are quite a number of hydroids that are found only in fresh water.

Bottom line.... hyposalinity will work for marine ich, but it won't for many hydroids.

[rkl303]

Ah thanks guys.