Identification, growth and ecology of larval and juvenile Urophycis chuss (Walbaum, 1792) and Urophycis tenuis (Mitchill, 1815) (Pisces: gadidae)

Methven, David Alan (1983) Identification, growth and ecology of larval and juvenile Urophycis chuss (Walbaum, 1792) and Urophycis tenuis (Mitchill, 1815) (Pisces: gadidae). Masters thesis, Memorial University of Newfoundland.

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Abstract

Pelagic Scotian Shelf Urophycis chuss and U. tenuis and Gulf of St. Lawrence Urophycis tenuis were identified using meristic, morphometric and pigment characters. These characters identify U. chuss and U. tenuis larvae as small as 5-7 mm SL. Pelagic U. tenuis are deeper bodied, have a higher caudal finray count and one less epibranchial gill raker than U. chuss. Adult complement of vertebrae, finrays and epibranchial gill rakers are developed for both species by 15.6 mm SL. -- Pelagic Scotian Shelf Urophycis chuss grow 0.9 mm per day or ca. 28 mm per month. Young-of-the-year demersal U. tenuis grow 1.4 mm per day or 42 mm per month reaching ca. 250-280 mm by December. Inquiline U. chuss, associated with the sea scallop Placopecten magellanicus grow 0.4 mm per day or 11 mm per month. Post-inquiline one-year-old U. chuss average a minimum of 200 mm SL. -- Nearshore arrival of pelagic juvenile Urophycis tenuis is delayed with increasing latitude. U. tenuis, a member of the summer ichthyofaunal arrive and remain nearshore when water temperatures are highest. Time of nearshore arrival and growth data indicate a winter-spring spawning period. U. chuss larvae are pelagic during summer and become inquiline during September-October on the Scotian Shelf. The presence of a larger U. chuss size mode may indicate that two different year classes occupy scallops at the same time. U. chuss prefer larger scallops.

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