Does your fish feel thirsty, pain and urine ?

The answer is simply YES. Some of them do but not all. As long as we distinctively set "thirst" differences between human and fishes.

There is also some differences for the fishes living in fresh water and sea water, and we also need to consider the possibility of the thirsty shark.

Bony fish, aka teleosts, have a salt concentration that is different from the concentration in the environment.

This also means that they live in an environment with a much higher salt concentration than is present in their blood. Their relatives in fresh water are in the opposite position.

Water usually move from higher concentration to lower concentration, a process of osmosis, through the membranes of the fishes. This, in a way, cause a constant leak of water through their body wall, gills and epithelia.

This is the part that answers the question : To replenish the lost water, marine fish is required to drink, so it would be ease their thirst. The excess salt they digest into their body by drinking seawater is excreted by specialised cells located in the gills.

While, freshwater fish, on the other hand, are unlikely to become thirsty. This is due to the fact that they live in a more dilute environment, and they have the opposite problem. Water tend to flows inwards to dilutes their blood.

The freshwater fish therefore need to excrete excess water, which they do in much the same way we do, through the fishes way of urinating...

So we can see that marine fish get thirsty and likes to drink in,
while freshwater fish will do the opposite, urine the excess water out.

LASTLY, for the sharks, dogfish, rays and skates - have little or no osmotic gradient between blood and seawater. This is because they can retain organic molecules, the main ones being urea (carbamide) and trimethylamine oxide (TMAO). In this way, the cunning sharks avoid an osmotic water flow from their body surfaces, and may not be very thirsty.

Stefan Nilsson, Professor of Zoophysiology, Göteborg University

FISH does feel PAIN !

New research, however, suggests that they may, revealing that their nervous system may be more complex than we thought—and our own awareness of pain may be much more evolutionarily ancient than suspected.

Joseph Garner of Purdue University and his colleagues in Norway report that the way goldfish respond to pain shows that thesevanimals do experience pain consciously, rather than simply reacting with a reflex—such as when a person recoils after stepping on a tack (jerking away before he or she is aware of the sensation).

In the study, the biologists found that goldfish injected with saline solution and exposed to a painful level of heat in a test tank will swim to and fro in one spot when placed back in their home tank.

Garner labels that “fearful, avoidance behavior.” Such behavior, he says, is cognitive—not reflexive. Other fish, after receiving a morphine injection that blocked the impact of pain, showed no such fearful behavior.

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