Nice idea, but reality is that it is not profitable or there is not enough margin.
To make any money you need to have high turnover so that cash keeps coming in so you can pay for staff and your fixed costs, rent , loans etc.
Most stores these days sell cheap novelty goods as they are cheap and bring in cash daily, but with marines nothing is cheap.
Also you need good cash reserves to fund growth and times when things are quite. most Business's these that don't have good capital fail.
unfortunately the pet industry is not doing great, it is far too competitive, to many selling on trade me/ online stores which is killing it.