There are some courses tailored to those wanting to work in the fishkeeping trade. Sparsholt College has a famous course, but lots of places offer more or less similar courses as well.
To be honest, none of them tell you anything a reasonably advanced hobbyist doesn't already know; but they are very good courses for people who aren't expert fishkeepers but do want to be able to sell or maintain ornament fish species successfully. At the very least, they are useful things to put on your CV if you want to work in the retail sector.
If you interest goes beyond the basic things like filtration and disease, then you'd be better served with a more academic course. The Open University and the Workers Educational Association are, in the UK at least, the two best avenues for this. They cater to different markets though. The OU is essentially a way for people to do proper degrees without the need to leave home or employment; the WEA produces short, low-cost courses across a few weeks more for entertainment rather than qualification.
Marine biology is a good subject, but one does need to be realistic about what it covers and what avenues it opens up. Fish biology is a relatively minor component at most schools. Fisheries management tends to be quite important though, but it's mostly a "numbers" based science, since it's all about modelling populations and how they react to fishing pressure. On the other hand, if you're interested in fish biology and would like to actually work with wild fish populations or do some lab work on them, a degree in (general) zoology is probably as good a way to get started as any. Academic research on fish tends to be focused primarily on edible species, either through fisheries management or aquaculture, but fish are also very important animals for lab-based work of various kinds, particularly animal behaviour. While it's not my cup of tea, fish are also very important for use in genetics, DNA-based taxonomy, and developmental biology, but while these subjects attract funding reasonably well, the work is intensely repetitive and unless you care about minutiae, numbingly dull.
If you're serious about learning about fish, and just want to learn about how they work, their evolution, their distribution, and their ecology, then by far the best thing you could do is grab a copy of "The Diversity of Fishes". It's a classic textbook, and covers just about every aspect of fish biology in a detailed but very readable way. It's expensive, but honestly, it's a book I've used almost constantly since I bought my copy over ten years ago. Perhaps your local library system can arrange an inter-library loan for you? That way, you can test-drive it first, and then decide if you want to invest in a copy.
It's almost always true that anyone interested in general, old-fashioned, David Attenborough-style natural history should avoid a career in science like the plague. Virtually no graduates ever get to do fun stuff that involves trips to coral reefs or playing with dolphins. The vast majority of people with bachelor degrees in science won't be able to find job in their field. Almost all masters degrees studentships, PhD studentships, and then post-doc studentships attract massive numbers of applicants. The students who succeed are the ones prepared to give up their social life and ambitions for things like home ownership or nice cars; instead they have to work 7-days a week, 10+ hours a day, for very low amounts of money. And if you don't want to do that, then there will certainly be a student from Asia who will, and frankly, that's all the professors care about. It's a depressing business really, and my advice to young scientists is invariable "don't, unless you're 100% dedicated" because only the people who live and breathe science succeed.
The happiest "naturalists" are those who do it as amateurs, a word coming from the Latin meaning, "for love". Naturalists can have other jobs for money, on the hours they want, and fill their weekends and holidays with field trips to wherever they want. No grant applications, no peer review, no need to slave away in a lab all night.
Hmm... ranting a little bit here, but hope this is useful.
Cheers, Neale
thank you for the heads up, i've not had a chance to look through it yet & hadnt noticed, I will go dig it out.
