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Circadian rhythms in juvenile american shad, Alosa sapidissima
Author(s) -
Katz H. M.
Publication year - 1978
Publication title -
journal of fish biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 115
eISSN - 1095-8649
pISSN - 0022-1112
DOI - 10.1111/j.1095-8649.1978.tb04208.x
Subject(s) - alosa , biology , circadian rhythm , juvenile , photoperiodism , moonlight , diel vertical migration , fishery , predation , rhythm , fish <actinopterygii> , zoology , day length , nocturnal , ecology , endocrinology , medicine , fish migration , horticulture
Swimming activity (in cm s −1 ) of a school (55 individuals) of young‐of‐the‐year (x̄ total length=110 mm) American shad, Alosa sapidissima , was determined under a variety of photoperiod conditions. These included a normal (ambient), a shifted, and constant‐light day. Swimming activity was measured over 4‐day periods. During normal days swimming speeds followed periods of about 24 h, with fast speeds (up to 45 cm s −1 ) and schooling occurring during the photoperiod. Under dark conditions speeds were slower (8 cm s −1 ) with most fish swimming as individuals. During a shifted day swimming speeds and schooling corresponded to the imposed day. Under constant light (equivalent to bright moonlight) no schooling was evident, and a constant, but slow, swimming speed was observed in each 24‐h period. These shad demonstrated an exogenous rhythm with respect to the imposed day length. It is hypothesized that an endogenous circadian rhythm would only be of use to a fish required to hunt or chase its prey. Shad, being plankton feeders, do not chase prey and therefore can exhibit an exogenous circadian rhythm with no detrimental feeding results.