Subject: Why does mammalian liver contain more catalase than bird and fish liver?l

As part of my coursework I have chosen to do an experiment, the aim of which is 
to find out how the amount of catalase found within the livers of different 
types of vertebrae (i.e. mammalian liver, bird liver and fish liver) varies.  I 
have completed the experiment, which involved adding a known amount of 2% 
hydrogen peroxide solution to a known amount of liver filtrate and measuring 
the amount of Oxygen given off.  My results (having done 5 repeats) show that 
mammalian (lamb's) liver contains the most catalase (26cm3 of oxygen was given 
off), bird (chicken's)liver contains slightly less catalase (24cm3 of oxygen 
was given off) and fish liver contains the least catalase (only 20cm3 of oxygen 
was given off). 
 
Now I have these results I am having trouble explaining why this is the case.  
Why does mammalian liver contain more catalase (per cubic cm) than bird liver, 
which contains more catalase (per cubic cm) than fish liver.  Does it have 
something to do with different levels of metabolic rate? being warm or cold 
blooded? the size of the animal?
 
Please send me an answer and/or any other information you may have on the 
subject.  Any help you could give me would be so appreciated because I have hit 
a dead end and can find no relevant information online.  I have also asked this 
question to enzyme.co.uk and they didn't know the answer but recommended I ask 
you.  Many thanks in anticipation of your reply,
 

Re: Why does mammalian liver contain more catalase than bird and fish liver?l