Can just 1 Neon Tetra be sick?

[Shadesiscool]

Hi
Very new to the fish world. Really enjoying the hobby but just so many questions!
Short back story.. -had a 10g tank for around 6-8 weeks. Cycled for 3 weeks before adding 5 Neon tetras. They seem happy. Within the past week I have purchased a Betta and some live plants. So had a little move around within the tank but nothing major.
It’s been 4-5 days now and 1 of my tetras is very pale and seems to be all the time. Water parameters seem fine and the fish appears to be behaving normally eating/bright/alert..no sign of fungal infections

Find it strange how it’s just the one fish ?!?
Anyone had this before ? I’m pretty sure it’s not related to light unless it’s become blind in the past couple of days !!?
Thank you ! 😀

[Ipalarez]

The fish is either old or got sick. Did you quarantine your betta and plants? Neon tetras are very sensitive, i've struggled keeping them in the past because they seem to be the first fish affected by anything

[Autumnsky]

It is possible that the Betta was aggressive to the fish and injured/bullied it. Or if it was just ill, as mentioned above, it can be tricky getting them to survive at the start.

The link in my signature is a very useful resource, might find a little new info there on getting off to a good start and staying well.

[charliebankston]

Fish can tell when another is sick or stressed (or both) and will harass it and often finish it off. Reminds me of watching nat geo where the lions pick the weak member of the herd off for lunch