CHH, on osmoregulatory parameters in a freshwater crustacean. The effects of eyestalk ablation and CHH

exposed to a wide range of salinities. According to the salinity of the medium, they are submitted to osmotic water exchanges and diffusive ion movements between their hemolymph and the external medium. In order to maintain their hydromineral balance, euryhaline crustaceans are able to regulate their body fluid through a decrease in the tegument permeability and an active uptake or excretion of ions (reviewed by Mantel and Farmer, 1983; Lucu, 1990; Péqueux, 1995). Few decapod crustaceans (mainly crayfish, along with Potamoidea crabs and a few Caridea shrimps) are fully adapted to freshwater (FW), where they spend their entire life cycle. These FW decapods, whose ancestors have supposedly originated from seawater, face a constant influx of water and loss of ions. Studies on crayfish osmoregulation have demonstrated that these crustaceans hyperosmoregulate in FW, and thus maintain a high hemolymph osmolality and ion content, through three main physiological mechanisms: (1) low permeability of the chitinoproteic cuticle to prevent water invasion and ion loss; (2) active uptake of ions (essentially Na+ and Cl–) by specialized cells, or ionocytes, located in the epithelia of the branchial chambers and (3) production of hypotonic urine through the excretory antennal glands (reviewed by Potts and Parry, 1964; Mantel and Farmer, 1983; Péqueux, 1995; Wheatly and Gannon, 1995). Since the early work of Scudamore (1947), numerous experiments have established the existence of neuroendocrine control of hydromineral metabolism in decapod crustaceans, mainly in marine species. The presence of active factors has been suggested in neuroendocrine centers located in the eyestalks, the pericardial organs, the cerebroid ganglia, the thoracic ganglionic mass and the ventral nervous system (reviewed by Kamemoto, 1976, 1991; Kleinholz, 1976; Mantel, 1985; Muramoto, 1988; Morris, 2001). Generally, 979 The Journal of Experimental Biology 206, 979-988 © 2003 The Company of Biologists Ltd doi:10.1242/jeb.00178