You don't need to work with cord that spans the length of your entire project
You have a couple of options that depend on what aesthetic you are trying to achieve and what you are willing to accept as far as look.
Adding cord with knots
There is a family of knots used to add in new cords to your project. Mostly suggested as a means of adding more colours or ...
In many macrame projects you mostly tie with only a part of the ends, the rest are just there waiting for their turn.
Your knitting fish work well for the 'waiting' ends, making the few that work at the time less likely to get in tangles.
Or, if you do not have those fish, bundle the string and tie the end around it or use a small elastic band.