Notes on the Biology of the Gobiid Fish Sicydium plumieri in Puerto Rico

Seven synonyms of Sicydium plumieri (Bloch) are listed and vernacular names for this species of goby at various West Indian islands are given. Adults of S. plumieri live in freshwater. They are strong swimmers, and their ventral sucking disk enables them to cling to rocks in swiftly moving water. The young can move up a vertical wet surface. In the rivers and streams this goby feeds by grazing slime algae such as desmids from stones. It can change its color rapidly from black to pale tan to match its background; it is usually dark because dark rocks predominate in the natural habitat. Differences between the sexes in shape of genital papilla, width of head and body, and height of fins are noted. Males exhibit bright nuptial colors from May to October, and have been observed in apparent display of this color to females from pinnacles of rocks in stream beds. Gravid females were collected in April, June, and July, but no eggs have yet been found laid beneath rocks in streams. Postlarvae migrate upstream from the sea in enormous numbers from July through January; the largest runs occur from September to November. The runs last about 2 days and begin from one to two days after the third quarter phase of the moon. The postlarvae collected in the sea have higher, more compressed bodies and average 3 mm longer than river fish. Sea postlarvae are transparent and usually scaleless when they start their migration upstream. Soon after entering the river, dark bands appear on the body. Scales first appear on the caudal peduncle of the slightly shrunken river migrant and develop progressively forward on the body. Shortly after the young settle to the bottom, the tail alters from emarginate to truncate, and becomes rounded with further growth. The banded color pattern becomes less intense after a size of 30 mm total length is reached and disappears entirely by a length of 40 mm. The postlarvae are preyed upon heavily by terns, snooks, grunts, and large gobioid fishes such as Gobiomorus and Eleotris. The young, which are regarded as a delicacy in the West Indies, are of commercial importance.