Effect of salinity on the metabolism and osmoregulation of selected ontogenetic stages of an amazon population of Macrobrachium amazonicum shrimp (Decapoda, Palaemonidae)

Abstract

Probably as a function of their wide geographical distribution, the different population of Macrobrachium amazonicum shrimp may present distinct physiological, biochemical, reproductive, behavioral, and ecological patterns. These differences are so accentuated that the existence of allopatric speciation has been suggested, although initial studies indicate that the genetic variability of populations happen at an intraspecific level. Among the biological responses described for M. amazonicum populations, those regarding osmoregulation and metabolism play a key role for being related to the occupation of diverse habitats. To this effect, we investigated osmoregulation through the role of free amino acids in cell volume control and metabolism, through oxygen consumption in larvae (zoeae I, II, V and IX) and/ or post-larvae of a M. amazonicum population from Amazon, kept in aquaculture fish hatcheries in the state of São Paulo. The results add information regarding the existence of distinct physiological responses among M. amazonicum populations and suggest that possible adjustments to metabolism and to the use of free amino acids as osmolytes of the regulation of the larvae and post-larvae cell volume depend on the appearance of structures responsible for hemolymph osmoregulation like, for example, the gills. In this respect, we verified that zoeae I do not alter their metabolism due to the exposition to fresh or brackish water, but they reduce intracellular concentration of free amino acids when exposed to fresh water, what may suggest the inexistence or inefficient performance of the structures responsible for volume regulation and hemolymph composition. On the other hand, in zoeae II and V exposed to fresh and brackish water, metabolism alterations were not followed by changes in free amino acids concentration. Thus it is possible, as the structures responsible for osmoregulation and ionic regulation become functional, that the role of free amino acids gets diminished and oxygen consumption elevated, probably due to greater energy expenditure with the active transportation of salts through epithelial membranes. Osmotic challenges also seem to alter throughout development, given that in zoeae II oxygen consumption is elevated on brackish water of 18, but in zoeae V it happens in fresh water. After M. amazonicum metamorphosis, free amino acids begin to play an important role as intracellular osmolytes, because we verified an increase of up to 40% in post-larvae exposed to brackish water of 18. The main free amino acids involved in cell volume regulation of ontogenetic stages evaluated were the non essential ones: glutamic acid, glycine, alanine, arginine, and proline. Interestingly, larvae from estuarine population studied here survived until the zoeae V stage in fresh water, but in some populations far from the sea, zoeae die right after eclosion in fresh water or they do not reach zoeae III stage. In addition, given that in favorable conditions caridean shrimp larvae shorten their development, we may inf...

Are there any physiological differences between the male morphotypes of the freshwater shrimp Macrobrachium amazonicum (Heller, 1862) (Caridea: Palaemonidae)?

“…The energy expended in metabolic processes, the total sum of all chemical reactions taking place in an organism, as measured by oxygen consumption, is used for the maintenance of homeostasis, including locomotion, growth, and reproduction (Diaz-Iglesias et al, 2012;McGaw et al, 2013;Mazzarelli et al, 2015). The individual oxygen consumption rate in M. amazonicum is directly related to the size of the animals, and it is higher in the GC1 and GC2 morphotypes ( Table 1).…”

Abundance and spatial-temporal distribution of Macrobrachium surinamicum Holthuis, 1948 (Palaemonidae) in the Amazon estuary, north of Brazil

“…However, this factor did not influence significantly the abundance of M. surinamicum in this estuary. Mazzarelli et al (2015) verified that zoeae I of M. amazonicum do not alter their metabolism due to the exposition to fresh or brackish water, but metabolism alterations were not followed by changes in free amino acids concentration in zoeae II and V exposed to fresh and brackish water.…”

Oxygen consumption remains stable while ammonia excretion is reduced upon short time exposure to high salinity in Macrobrachium acanthurus (Caridae: Palaemonidae), a recent freshwater colonizer

“…In addition, penaeid marine shrimps are hyper-hypo-regulators (Péqueux 1995, Freire et al 2008b, as opposed to palaemonid shrimps, which are essentially hyper-regulators, as already mentioned. In the results of an experiment with M. amazonicum at different ontogenetic stages (zoea I, II, V, and IX) exposed to different salinities (0.5, 6, 12 or 18 psu), there was a greater consumption of oxygen at 0.5 psu in the zoea stage V, probably due to the great amounts of energy required for the active transport of salts through the epithelia (Mazzarelli et al 2015). A similar pattern was observed in M. tuxtlaense, an strictly freshwater prawn exposed to a salinity gradient (0,5,10,15,20,25, and 30 psu): higher rates of oxygen consumption in the shrimp M. tuxtlaense were observed at low salinities (0, 5 and 10 psu), to account for hyper-regulation of the osmolality of the hemolymph (Ordiano 2005).…”

“…Some palaemonid shrimps exposed to salinity increases, for instance Macrobrachium heterochirus (Wiegmann, 1836) and Macrobrachium potiuna (Müller, 1880), experience a decrease in metabolic rates, while the diadromous Macrobrachium acanthurus (Wiegmann, 1836) and Macrobrachium olfersii (Wiegmann, 1836) experience a peak in their metabolism-salinity curves ("dome-shaped curve") close to their isosmotic point, ~21 psu (Moreira et al 1983). In another diadromous shrimp, Macrobrachium amazonicum (Heller, 1862), oxygen consumption was lower in freshwater than in 18 psu in zoea II, and was higher in freshwater than in 12 and 18 psu in zoea V (Mazzarelli et al 2015). The freshwater shrimp Macrobrachium tuxtlaense Villalobos and Alvarez, 1999, when exposed to increased salinities up to 30 psu, has shown an increase in oxygen consumption in 5 and 10 psu, and a decrease in this parameter in the other salinities, with respect to the control salinity, fresh water (Ordiano et al 2005).…”