Help catching legendary fish

by Smusk posted Aug 12, 2020
Despite fishinf alot, i have only been able to catch up azure dragon snakeheads as my legendary fish catches at this point in time (15+ times at the time of writing thus post).
Are there any specific requirements i need before i can catch the other two?. (Purple ayu and king criprinsus) Like rank, time of day, how far to throw out your line etc.
Please help, i really want to finish up my collection.