Proper fixation is critical. We have used a buffered media with glutaraldehyde (electron microscopy grade) at 5 °C before sending it to our microscopy service for further processing. Remember that the osmolalilty is critical, especially with fish spermatozoa. You have to prevent activation, thus using a medium isoosmotic to seminal plasma. If fixation goes well, usually a typical SEM protocol should work.

I've never worked with fish sperm, but I believe Felipe Martínez-Pastor gave you a sound advise. 

Just remember: never put biological specimen in clear water or ethanol prior to fixation.

Use proper solvent/buffer for fixative (it may depend on whether your work with sea fish or with fresh water one).

Thoroughly wash out buffer/fixative with clear water after fixation (to avoid crystals)

Use proper dehydration technique (standard procedure).

Centifugation may be required in between steps.

am working with marine fish, today i tried with ethanol but am not getting good result.

I work with mammalian semen, but i have not really worked on fish. but i will suggest you to do washing. This technique uses dilution and centrifugation. A sperm wash solution like coelomic fluid to get rid of the seminal plasma and other materials, before the SEM protocols.

I can refer you to one study have done before on sturgeon spermatozoa which may show you the way. In that work our colleagues fixed sperm samples with 2.5% glutaraldehyde in 0.1M phosphate buffer, stored at 4 ◦C and  samples were postfixed and washed repeatedly for 2 h at 4 ◦C in 4% osmium tetroxide and dehydrated through an acetone series.

You may find more details the procedure on :

 Hatef, A., Alavi, S.M.H., Baradaran Noveiri, S., Poorbagher, H., Alipour, A.R., Pourkazemi, M. and Linhart, O., (2011). Morphology and fine structure of Acipenser persicus (Acipenseridae, Chondrostei) spermatozoon: Inter-species comparison in Acipenseriformes. Animal Reproduction Science, 123: 81-88.

( DOI:10.1016/j.anireprosci.2010.10.013)

good luck

I have never worked with sperm before however we work with many different cells types...to prepare any of our samples we dilute samples (~5ml) in PBS, filter through a track-etched polycarbonate filter. This is followed by a series of ethanol washes (2ml each of 50%, 75%, 85%, 95% and 100%). The filter is air dried and the mounted and gold coated. This has worked for all sample types prepared to date.

Hope that helps

Sci Rep. 2015 Mar 30;5:9505. doi: 10.1038/srep09505.

A mobile biosafety microanalysis system for infectious agents.

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