Biotemas (Sep 2007)
Determination of the grow-out density of Farfantepenaeus paulensis (Perez-Farfante, 1967) shrimp juveniles with a view to providing alternative culture structures (pens) in Ibiraquera Lagoon, Imbituba, Santa Catarina
Abstract
Ibiraquera Lagoon, which is located between the municipalities of Garopaba and Imbituba, both in Santa Catarina, a state of southern Brazil, was set up in the last decade as part of a Program for the Restocking of Coastal Lagoons. This program obtained successful results for several years. However, nowadays the productivity of this natural environment has probably been reduced because of its overfishing, specially of the pink shrimp Farfantepenaeus paulensis (Perez-Farfante, 1967), and above all the effect of anthropogenic factors. Such facts have led some researchers to question the viability of successfully restocking the lagoon, since eutrophication would be accelerated by several other factors. Thus, to discover whether the young of F. paulensis could grow and survive feeding only on the natural food of the lagoon´s environment, and whether they were able to tolerate the quality of the water, an experiment was designed to calculate how the lagoon would support future restocking. To this end a farming process was set up which lasted 93 days, testing 3 different densities: 1, 1.5, and 2 shrimps/m2 in standard circular pens of 50 m2. Results after the farming period regarding growth the physico-chemical parameters indicated values in the expected range that fell within the tolerance limits for the survival and satisfactory development of the young of F. paulensis, since significant differences in the daily fluctuations of the dissolved oxygen (OD) were not found. Results on the growth were also found to have similar values to those found by other researchers in the dos Patos Lagoon, in the neighboring state of Rio Grande do Sul. Treatment with a density of 1 shrimp/m2 was significantly different (p<0.05) in relation to the other two treatments with densities of 1.5 and 2, both of which had very similar values. However, the final results of shrimp survival and polychaeta biomass throughout the experiment did not present significant differences (p<0.05) among the three treatments. It is noteworthy that polychaeta was not found in the sample measured after the 65th day of the experiment and that other taxonomic groups of the zoobenthos must have replaced the polychaeta in the diet of the shrimps. In conclusion, it may be affirmed that the Upper Lagoon (one of the three parts in which Ibiraquera Lagoon is divided) has very good conditions for future restocking if it is done with the density of 1 shrimp/m2, and also that the young of F. paulensis pink shrimp should be able to adapt, grow and survive the biological and physical conditions of the water and natural food of the lagoon.
