If you have spatial analyst for ArcMap you could do this rather easily. I'll refer to your raster as FishRaster in my following example:
Geoprocessing Tools> ... (I'll use the below format to refer to the path to tools):
Geoprocessing Tools> Spatial Analyst> Map Algebra> Raster Calculator
First step: We need to get your raster in 1's and 0's to target the 1's for zonal stats.
FishRaster < 2
This creates a raster of ones and zeros, ones where the value you wanted divided is located only.
...Spatial Analyst> Zonal> Zonal Statistics
Input Raster = FishRaster
Zone field= Value
Input value Raster = FishRaster
Output raster = output1
Statistics type = SUM
This will create a raster which will have the sum of all 1 cell's value replacing the 1s that were there. Read the value, and we'll use that (MaxValue) for the next step.
The next step could be done using the raster calculator, but it will give you an integer output unless you force it into a floating point raster:
output1/(MaxValue) ... should result in all zeros.
output = float1
then to raster calculator, divide float1 by (yourNumber)
This will leave you with 0's and fractions. You mentioned you wanted those 0's to be 2's; you can use Con or Reclassify. Reclassify may force everything to integers, however, and Con statements are a pain to figure out.
At least this will get you a distinguishable list of values which you could do a study with. I can only assume you're doing some sort of density study.