We analyses fish blood for red cell and white cell when we sampled (as soon as possible). I only stocked blood serum without any protectant and we could analyses serum biochemical enzymes again and again. But I don't know if you could preserve fish blood.

This article : "Preserving whole blood in formalin extends the specimen stability period for manual cell counts for fish."  used 10% formalin and concluded to be a reliable method to maintain cell morphology for manual counts for up to 1 month.

I was just wondering if anyone had experimented with their method or something similar.

I will try to count the blood samples ASAP but I have other samples to take and process ASAP (for respiratory burst and phagocytic activity of peripheral blood leukocytes)

For anyone with the same issues (too many things to do at the same time!) then formalin in PBS is great for preserving fresh blood for cell counts. I went as high as 5% formalin but 1% worked well to maintain my samples for up to 24h( which was more than enough for me. 10% formalin changed too much the coloration/shape of cells in Siganus