JOURNAL OF PLANKTON RESEARCH | VOLUME 25 | NUMBER 11 | PAGES 1347-1358 | 2003
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The paralarvae of two South American sympatric squid: Loligo gahi and Loligo sanpaulensis
Centro Nacional Patagónico, Consejo Nacional De Investigaciones Científicas Y Técnicas, Boulevard Brown S/N, Puerto Madryn (9120), Chubut, Argentina
* Corresponding Author: baron{at}cenpat.edu.ar
Two loliginid squid inhabit coastal and continental shelf waters of the south-west Atlantic off Argentina: Loligo gahi D’Orbigny, 1835 and Loligo sanpaulensis Brakoniecki, 1984. Even though L. gahi is associated with colder and deeper waters than L. sanpaulensis, both are sympatric in part of their geographic and bathymetric ranges of distribution. As in many other cephalopod species, there are no detailed descriptions of the ‘paralarvae’ (planktonic larvae of the cephalopods) of these species useful for identification of individuals captured in plankton samples. In this study, size, morphometry and patterns of chromatophore abundance and distribution were characterized for hatchlings (hatching paralarvae) of these two species obtained in the laboratory after egg incubation at different temperatures. Paralarvae from both species were captured in preliminary plankton surveys conducted off the coast of Central Argentina, and were characterized on the basis of their morphometry. Differences were observed in the dorsal mantle lengths of the hatchlings of L. gahi (2.3–3.7 mm) and L. sanpaulensis (1.4–1.7 mm). Average size and number of dark chromatophores at hatching were negatively correlated with incubation temperature in L. gahi. Although most morphometric indices showed between-species differences, fin length to mantle length ratio was markedly higher in L. sanpaulensis. Patterns of chromatophore abundance and distribution allow the hatchlings of both species to be differentiated from each other and from those of other Loligo species. Hatchlings of L. sanpaulensis have two red chromatophores on the ‘cheek patches’ areas, while those of L. gahi have three to five. On the dorsal surface, the hatchlings of L. gahi display dark brown chromatophores, which were absent in L. sanpaulensis. Hatchlings of L. gahi were found at outer shelf and costal stations off Northern Patagonia. Paralarvae of L. sanpaulensis were found at coastal stations off the Buenos Aires Province and off Northern Patagonia.