As a 2nd year nephrology fellow I am now doing some work in a lab which studies zebrafish kidney development. Here is an example of a control (wild-type) zebrafish at 54 hours post-fertilization.
If you use a morpholino (a form of antisense technology) to knock down a gene important for kidney function, you get massive edema after 3-4 days–as shown in the photos below. This is because zebrafish (a type of minnow native to India) live in freshwater, where the osmolarity is much lower than the intravascular osmolarity; with loss of renal salt and water homeostasis, volume overload ensues. This condition can be mitigated by putting the fish in saline water approximating the fish’s endogenous osmolarity.