In the aquaculture industry, there is the never-ending quest for replacement ingredients for fish feed. In this study they are looking Spirulina as a replacement for fishmeal, which is more expensive. What did the study find out: yes that adding Spirulina does help with the grow out of young fish.  But the weakness of the study is that the study is only a 12 week study. 
 
"This study was designed to investigate the effect of different replacement levels of fishmeal with Spirulina on weight gain and Survival rate of common carp Cyprinus carpio L., the trial was conducted for 105 days and for this purpose 200 fingerlings common carp with an average weight 32.7 g were brought from a local market."
 
https://docsdrive.com/pdfs/ansinet/pjn/2014/93-98.pdf