Plural forms of some nouns

[nyota]

Hi,
I'd like to ask about the usage and forms of nouns such as:

nucleus - (pl) nuclei, nucleuses
Do the two forms denote different meanings? I was wondering if the specialised meaning (part of an atom, part of a cell) takes nuclei while the more general one (a group of people/things essential to something) goes for nucleuses.

solo - (pl) soli, solos
Again, any contextual changes in the usage? Is soli preferred with classical music/musical pieces?

index - (pl) indexes, indices
I know there IS a change of meaning here, only I'm not sure which means what.

matrix - (pl) matrixes, matrices
Matrices as a mathematical term and matrixes as a general one (structure)?

mouse - as a computer device; I know it doesn't often appear in the plural but the question has been bugging me since I spotted it in some long-forgotten post. Is mice common in this sense?


And now something fishy

trout and salmon don't have a separate plural forms BUT is it possible with herring and carp? (pl) herring, herrings; (pl) carp, carps?

Trout, salmon is/ are...
Herring/ carp is delicious.
How many herrings/ carps...?

Are these correct?


Thanks for help

[nyota]

To continue...

In what sense/ context would you use:

gallows is/ gallows are
kennels is/ kennels are
alms is/ alms are
ninepins is/ ninepins are
bellows is/ bellows are

mediums/media
terminuses/termini
virtuoses/virtuosi

Thanks again for any hints