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Q.
The excretory material of bony fish is :
Delhi UMET/DPMTDelhi UMET/DPMT 2001
Solution:
The excretory material of bony fish is ammonia i.e., ammonotelic. Ammonia is highly soluble in water with which it forms ammonium hydroxide $\left( NH _{4} OH \right)$.
The latter passes readily across the cell membranes and is dispersed into the surrounding water.
Excretion of urea is known as ureotelism and the animals which excrete urea are called ureotelic.
Ureotelic animals include Ascaris, earthworm, cartilaginous fishes like sharks and sting rays, semi-aquatic amphibians.
Certain invertebrates like some molluscs (Unio, Limnaea etc.) and some echinoderms (e.g., Asterias) excrete excess amino acids as such.
These animals are called aminotelic and their mode of excretion is called aminotelism.