8 month old not eating

[galaxy84]

Since we had our mini schnauzer neutered a month ago he's become really funny about food.

He is on two meals a day but his kibble is just sitting there all morning and he might have a nibble of it late afternoon, and then tends to be a bit better about eating his evening meal, but is not eating nearly enough to meet guidelines.

He watches me prepping it but rather than pounce on the plate as soon as it's down like he used to, he now just looks at it suspiciously from afar and then gives it a wide birth.

He is going to the toilet fine and seems his usual bouncy self.

He is hungry as he'll get very excited and do loads of tricks for treats (cooked meat, cheese etc...). He is definitely not getting enough treats to fill him up and no one is secretly feeding him human food.

I don't know what to do. Is it worth a trip to the vets? Should I change his food?