The process continues so that larger, older fish have higher concentrations of toxic chemicals.
This means that a healthy cod population must include relatively large numbers of older fish.
During the war, though, most of the populations rebounded, with older fish showing the biggest increase.
He had a weird growth along his dorsal fin, and that gape-mouth grimace you see in older fish.
Explaining the process, Mr. McIntyre, a bearded sailor from central casting, said: "An older fish has a browner bloodline.
The spawn of younger fish do not seem to be as robust as the spawn of older fish.
They range from fingerlings that might be this year's spawn to older fish of up to 20 pounds.
Food robots dispatch brine shrimp for the newly hatched and dry feed for the older fish at synchronized times.
Moreover, the young of some fish species needed to follow older fish to learn how to reach their spawning areas.
"There are these two young fish swimming along and they happen to meet an older fish swimming the other way, who nods at them and says, 'Morning, boys.
By David Means He had a weird growth along his dorsal fin, and that gape-mouth grimace you see in older fish.
