🐟 Two fish farms, two completely different waters

Fish are cold-blooded: their bodies sit at whatever temperature the water is. So every kind of fish has water it does well in. Rainbow trout are a cold-water fish. Channel catfish are a warm-water fish, and they eat and grow fastest in summer heat.

Basis: Fisheries biology: fish are ectotherms, so water temperature sets their body temperature and how fast they grow; rainbow trout are classed as a cold-water species and channel catfish as a warm-water species.

Cold water comes with a bonus. The colder water is, the more oxygen it can hold — and water that keeps moving keeps picking up more. That is why a trout farm is built as a long channel with spring water running through it, while a warm, still catfish pond has to be watched carefully: in mid-summer the oxygen falls lowest just before dawn, so farmers keep machines churning the surface.

Basis: Physical chemistry: oxygen dissolves less easily in water as the temperature rises. Catfish pond management: dissolved oxygen is at its lowest at dawn in mid-summer, and ponds are aerated to keep the fish healthy (Mississippi State University Extension).

The land matters as much as the water. Delta catfish ponds are built on flat ground, with the soil dug out of the middle piled up into banks around the edge — and that soil is heavy with clay. Water creeps through clay very slowly, so the pond behaves like a giant bowl instead of a leaky bucket.

Basis: Pond construction guidance: levee ponds are built on flat land by moving soil from the pond bottom into surrounding embankments, on soil with enough clay content to hold water (Mississippi State University Extension).