Factors affecting the immigration of postlarval penaeid shrimp into a Mexican lagoon system

Penaeus californiensis , P. brevirostris , P. vannamei and P. stylirostris occur in western Mexico, and all breed in the sea. P. californiensis is the dominant species in commercial catches from the sea and P. vannamei from coastal lagoons. Observations are summarized on the laboratory behavior of postlarvae of these species and on their distribution in relation to environmental factors in the channel (estuary) linking Huizache Lagoon to the sea. This estero (estuary) which is about 10 km long, has a lower salinity than the sea only from July to November. The net tidal flow in the estuary is lagoonward from February to July and seaward from August to January. In the laboratory, postlarvae of all species preferred lower salinity than the one to which they were acclimated; estuary water was preferred rather than sea water of a similar salinity by the two species tested. Postlarvae did not consistently swim with or against currents. There was no evidence that their direction of swimming was influenced by changes in light, salinity or the type of water or endogenous factors. On the other hand, postlarvae showed a marked tendency to leave the bottom layers with the tidal flood. Passive drift with the flood tide probably provided the chief method of movement