If fish are dying in the bag on the way home it is from stress. It can be from someone chasing the fish around the tank for several minutes before catching them, or the fish might have only come into the shop that day or the day before and the stress of being caught out and bagged up kills them.
It's a good idea to find out when the shop gets their fish in, it might be Wednesdays, and you should buy fish the day before they come in. That way the fish you buy will have been in the shop tanks for at least 6 days before you buy them and they won't be as stressed out.
You want to try and avoid buying fish that have not been in the shop tanks for at least 3 days, and the longer they are in the shop tanks the less stress they suffer when moved to a new tank.
Re: fish being chased around before you buy them. A shop assistant should be able to catch any fish in a tank within a few seconds of the nets going into the tank. If they chase the fish all over the tank for a minute or more, tell them to stop and you will come back another day. One of the petshops I use to visit would allow me to catch my own fish. However, one day when I was there they had a new guy who wouldn't let me catch my own. He spent about 5 minutes chasing 6 fish around a tank and I told him to stop but he didn't. I took the fish and lost 3 of them on the way home and the other 3 died within a couple of days. I went back and spoke to the boss and he spat the dummy at the new guy because the fish cost a lot of money.
Basically to catch fish out of an aquarium you use two nets, 1 big and 1 small. You set the big net up and guide the fish into it with the smaller net. If the shop assistants chase fish around with 1 net, find another worker who knows how to catch fish.
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Some catfish get their pectoral fins caught in the mesh of some nets. I use white fine mesh nets for pictus catfish and clown loaches because if you use a green course mesh net they always get caught in the netting.
You want to try and get the netting off the catfish so it doesn't get infected and have issues.
It's a good idea to find out when the shop gets their fish in, it might be Wednesdays, and you should buy fish the day before they come in. That way the fish you buy will have been in the shop tanks for at least 6 days before you buy them and they won't be as stressed out.
You want to try and avoid buying fish that have not been in the shop tanks for at least 3 days, and the longer they are in the shop tanks the less stress they suffer when moved to a new tank.
Re: fish being chased around before you buy them. A shop assistant should be able to catch any fish in a tank within a few seconds of the nets going into the tank. If they chase the fish all over the tank for a minute or more, tell them to stop and you will come back another day. One of the petshops I use to visit would allow me to catch my own fish. However, one day when I was there they had a new guy who wouldn't let me catch my own. He spent about 5 minutes chasing 6 fish around a tank and I told him to stop but he didn't. I took the fish and lost 3 of them on the way home and the other 3 died within a couple of days. I went back and spoke to the boss and he spat the dummy at the new guy because the fish cost a lot of money.
Basically to catch fish out of an aquarium you use two nets, 1 big and 1 small. You set the big net up and guide the fish into it with the smaller net. If the shop assistants chase fish around with 1 net, find another worker who knows how to catch fish.
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Some catfish get their pectoral fins caught in the mesh of some nets. I use white fine mesh nets for pictus catfish and clown loaches because if you use a green course mesh net they always get caught in the netting.
You want to try and get the netting off the catfish so it doesn't get infected and have issues.