Partial purification of the crowding factor from Carassius auratus and Cyprinus carpio

Crowding factors are those substances released by fish, which, under crowded conditions, inhibit both their growth and reproduction and depress their heart rate. We have partially purified the crowding factor from goldfish and carp by following a heart‐rate‐depression assay. The heart‐rate‐depression activity eluted with the diglyceride fraction from both silicic acid and Sephedex LH‐20. A slightly different activity eluted with the free sterols. The peak activity associated with the diglycerides has a distinctive ultraviolet spectrum distinguishable from that of phthalic acid esters, which are also active in the assay sytem and are found in fish tissues and fish water.