Growth, oxygen consumption, ammonia-N excretion, biochemical composition and energy content of Farfantepenaeus paulensis Pérez-Farfante (Crustacea, Decapoda, Penaeidae) early postlarvae in different salinities
Introduction
Life cycle of most penaeid shrimp species includes migration from open sea to estuaries and vice-versa during specific phases of the ontogenetic development (Dall et al., 1990). The pink shrimp Farfantepenaeus paulensis is distributed along Southwest Atlantic waters (from 15° to 35°Lat S) and its life cycle comprises spawning in shelf waters (50–150 m) with planktonic larval development concomitant to the migration towards coastal zones (Valentini et al., 1991). After metamorphosis to decapodid (or postlarva), individuals penetrate estuarine grounds as mangroves and salt marshes. In these nursery areas, postlarvae develop until they reach juvenile age and migrate back to open waters, completing the cycle. Postlarvae must be able to cope up with the environmental fluctuations such as salinity after penetrating estuaries. In penaeids, the ability to support salinity variation increases simultaneously with the transition in life style from planktonic to a benthic existence (Charmantier et al., 1988). Such ontogenetic events may involve homeostatic mechanisms and efficient use of energy from food and body reserves. The understanding of energetic processes during early postlarval stages may indicate how adapted are individuals to such unstable environments, in which salinity is one of the most variable physical factors.
Salinity effects on the metabolism of decapod crustaceans have been well studied by measurements of oxygen consumption Kinne, 1971, Gaudy and Sloane, 1981, Chen and Lai, 1993, Chen and Nan, 1993, Chen et al., 1995, Péqueux, 1995, Villarreal et al., 1994, Jury et al., 1994 and ammonia excretion Gerard and Gilles, 1972, Regnault, 1987, Chen and Nan, 1993. However, throughout the ontogenetic development of decapods, specifically of early postlarvae of penaeids, these studies are still scarce (Gaudy and Sloane, 1981, Felder et al., 1986, Yagi et al., 1990, Anger et al., 1998, Rosas et al., 1999). The relationship between energy channeled into growth and to metabolic processes seems to be affected by salinity Anger et al., 1998, Rosas et al., 1999, and may imply in growth variation of cultured shrimp.
F. paulensis is one of the main fishery resources of Southern Brazil Valentini et al., 1991, Gasalla and Tomás, 1998 and has been cultured commercially since early 1990s (Vinatea and Andreatta, 1997). Recently, the cultivation of this species has decreased mainly due to insufficient knowledge on physiology and nutrition (Lemos et al., 2000) that avoided prediction of its growth performance in captivity. In the present study, growth, oxygen consumption, ammonia-N excretion, biochemical composition and energy content were determined in postlarvae (stages PL VI–VII and PL XIII–XV) of F. paulensis in different salinities. The stage PL VI–VII is predominantly penetrating estuarine zones D'Incao, 1991, Antunes and Calazans, 1997 and exhibits a transitional behavior from planktonic to benthic habits. Since PL X, a totally benthic existence is attained that is typical in the following stages of shrimp development (Iwai, 1978). Energy allocation into growth, metabolism and body reserves could be evaluated here at naturally occurring salinity levels of postlarval habitat.
Section snippets
Experimental shrimp
F. paulensis postlarvae were obtained from spawning of wild females induced to sexual maturity by eyestalk ablation Aquacop, 1979, Simon, 1982, Wyban et al., 1987. Larvae were cultured at 26±1°C and 34±1‰ according to Beltrame et al. (1996) and Lemos et al. (1999).
After metamorphosis to postlarva (PL), the diet was composed of microalgae Chaetoceros calcitrans with increasing amounts of artificial plankton (Nippai Shrimp Feed) and brine shrimp nauplii (Artemia sp.). From the fifth postlarval
Results
Postlarvae developed from PL VI–VII to PL XIII–XV in 13 days and development did not seem to be influenced by salinity (Table 1). On the other hand, growth was significantly affected by salinity (P<0.05), bearing greatest individual values at 25‰ (21.3-fold) followed by 15‰ (13.5-fold) and 5‰ (11.2-fold). The lowest growth was at 34‰ with only 8.2-fold weight increase. Regressions were set between individual dry weight and age while metabolic rates (oxygen consumption, ammonia-N excretion),
Discussion
After penetrating estuaries, penaeid postlarvae need to be able to cope up with large salinity variations. Postlarvae of F. paulensis reach the estuary around PL VI D'Incao, 1991, Antunes and Calazans, 1997 exhibiting a transitory behavior between planktonic and benthic, and adopting typical benthic habits after PL X (Iwai, 1978). Survival through such shifts of habits and habitat may depend on the efficient utilization of energy from food and body reserves Sasaki et al., 1986, Mourente and
Acknowledgements
Thanks are extended to Prof. E. Beltrame (LCM-UFSC) and all LCM staff for the supply of specimens and assistance in cultivation. D. Lemos acknowledges the financial support of Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Brazil, 96/03688-6). [SS]
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