Chemistry and materials science are difficult below the waves, breeding is slow but reliable. Breeding has taken the Icthyons from territorial catfish bullying smaller species for food to gracefully whiskered inheritors of a thousand useful creatures, well-bred and good breeders.
Symbiotes for health, parasites for control. Squid for hunting and barracuda for fighting. A good home is made by waste-eating snails. Octopuses as living tools. Everything is alive or was part of something alive.
The Icthyons have not spared themselves from their great breeding projects. Modern Icthyons are healthier, smarter, more ruthless, and have shorter lifespans than their ancestors, changes introduced through generation after generation of careful matchmaking.
It takes eons to breed stock into a new form. Innovation is virtually impossible, iterative improvement virtually inevitable. Icthyon culture prizes links to the past, and incorporates anything new slowly and thoroughly. Over the course 10,000 years, crab-silk was slowly bred from a disposable and temporary string, to sturdy fabric, to a woven sheets rivaling steel, and so over the course of 10,000 years, knotwork became increasingly sophisticated and fell out of favor, silk fashion became increasingly sophisticated and fell out of favor, and now silk armor is becoming increasingly sophisticated.