Isinglass
Fish-derived collagen that polishes whites to brilliance at a tiny dose.
Typical dose
Very low, around 5 to 25 mg/L; overfining coarsens rather than clears.
When to add it
On a nearly finished white or a sparkling base.
Legal limit
No specific limit that this reference states. Additions are still governed by the treating-materials rules where you make wine, so check them.
Vegan
No. Animal-derived, and usually an allergen to declare, so it rules out a vegan label and needs care on the ingredients list.
In practice
Gives whites a brightness other finings do not, at a fraction of their dose, but it forms a light, fluffy lees that is easily stirred back up, and it overfines readily. It is collagen from fish swim bladders, so it is neither vegan nor vegetarian and is an allergen to declare.
Others in fining and clarification
Bentonite
Adsorbs unstable protein to prevent haze in whites and roses.
Gelatin
Collagen that strips harsh tannin and astringency from reds.
Egg white
The traditional, gentle softener of barrel-aged red tannin.
Casein
Treats browning and light oxidation or taint in whites.
PVPP
A synthetic that removes browning, pinking and bitter phenols.
Kieselsol
A negatively charged fining, paired with gelatin for a compact lees.
Sparkolloid
A polysaccharide clarifier for stubborn hazes that resist other finings.
Activated carbon
A blunt last resort that strips colour and off-odours together.
Plant protein fining
A vegan substitute for gelatin and isinglass.
Diatomaceous earth
A filter aid, rather than a fining, for wines too cloudy to filter.