The Big Pet Store on Hereward Rise in Halesowen, was targeted in the raid.
Mike Burke, owner of the store, said the discovery was ‘devastating’.
He said: “It’s upsetting. The loss of the stock and money is one thing but it’s upsetting to find someone has done that to you in the first place. Who would want to do that?
“Our customers have been great, but it really knocks you back and it makes you think – why do you bother? It knocks you back and makes you feel terrible.
“We can go through the insurance company but to come here and see the door smashed in, your heart drops.
“We’re coming back – we’re strong. There’s a reason to do what we do.”
The pet store, which has been built up from a market stall, moved into its current location in 2005.
Darren Burke, store manager and Mike’s son, said it was ‘soul destroying’.
He said: “The chain on the main gate to the shop was broken and the locks on the front door were sawn off – and they had pulled the shutters back down.
“Things were missing inside the shop on the shelves and doors were kicked in.
“It was a mess and the messiest area was where we kept the fish, which they killed. The fish tank had water spilling over the top and the smell was bad.
“They had poured two whole bags of fish food into the tank.
“Stealing stock, that’s part is part and parcel of it, but I’m thankful we don’t sell any other animals. It seems vicious and pointless.
“It’s soul-destroying really.
“They stole our camera system and cut the phone line so we’ve not got any information of when they were in.
“It seems quite malicious, but we’ve got a really good customer business and they were so concerned about us.
“We’ve got such a massive response. Now it’s just about getting everything back to normality at a busy time of the year. It’s our busiest month and they stole our best-selling lines, which are still out of stock.”
The 32-year-old, who lives in Quarry Bank, said the store has increased its security.
He said: “Every time something happens we increase our security even more.
“I was very upset and you get really tearful when you get that call. All the staff were upset and it’s very hard.
“They go above and beyond for the store and it feels personal for them as well as us.”
The break-in happened sometime between 5.50pm on November 24 and 9.30am the following morning, stealing stock and killing fish at the store.
A police investigation is currently taking place.
A spokesperson for West Midlands Police said: “The matter remains under investigation by police and anyone with information should contact West Midlands Police via Live Chat at www.west-midlands.police.uk 8am - midnight, or call 101 anytime.
“To remain anonymous call Crimestoppers on 0800 555 111. Please quote crime number 20DY/274494G/18.”