If someone near you was looking for what you want to sell, what would be the first thing they do? Probably look online. Get yourself set up with a website and work on the SEO (search engine optimization) so you will show up towards the top of a search. You can do your own using website building companies, or you can hire someone to do your SEO.
Then determine if you are going to sell online and if so, make sure you have that feature to “shop” on your website. Companies like “Wix” make it easy to set up a website and include a shopping feature.
If you plan to ship live fish, check with your local shipping options to find out if any special certifications or permits are needed.
How are you going to promote and market your business? Can you do it locally with social media? Are you going to advertise with a local mailer? Will you make a flier and put it up on a bulletin board at another business that promotes local business owners?
Get yourself some business cards and attend local aquarium club events and pass your cards out. Anywhere you see other businesses leaving their business cards, put yours there too.
Make sure you ask everyone who does business with you how they found you so you can keep track of what marketing options are working.
Perhaps buy some company t-shirts and wear them everywhere (out to eat, at local festivals, when you take a walk downtown, etc.). The more people see your company name or logo, that will build familiarity. Then when they go looking for what you’re selling, they see your logo or company name and already feel familiar with it subconsciously. So just because nobody tells you they say your ad in a local mailer, that doesn’t mean the mailer didn’t stick with them subconsciously so when they saw your website they already felt familiar. They might tell you they found you on an online search. So all forms of marketing can be effective as a combination. I hope I am explaining that clearly.
Good for you, and best of luck!