Investigation of the control of urine production in the shore crab, Carcinus maenas L

Effect of Nitrogen Compounds on Shrimp Litopenaeus vannamei: Histological Alterations of the Antennal Gland

Two experimental modules with different stocking densities (M1 = 70 and M2 = 120 shrimp m^-2) were examined weekly during 72-day culture cycle at low-salinity water (1.9 g L^-1) and zero-water exchange to examine the effects of water quality deterioration on the antennal gland (AG) of shrimp. Results showed survival rates of 87.7% and 11.9% in M1 and M2, respectively. Water temperature, pH, dissolved oxygen, and chlorophyll a were not significantly different between modules but the concentrations of the nitrogen compounds were significantly different between modules with the exception of nitrite-N, showing a higher histological alteration index in M2 (32 ± 10) than M1 (22 ± 0) with a strong correlation with the nitrogen compounds. During the last weeks was evidenced in M1 inflammation and hemocytic and hemolymph infiltration, while in M2, melanization, hemocytic melanized nodules and cells with kariorrexis.

The role of the antennal glands in ion and body volume regulation of cannulated Penaeus monodon reared in various salinity conditions

Urinary production rate and the osmotic and ionic concentrations in both urine and hemolymph were measured in cannulated intermolt Penaeus monodon which were either abruptly transferred from 45 ppt seawater to 15 ppt seawater (Experiment 1) or acclimated to 5, 25 and 45 ppt seawater (Experiment 2). In Experiment 1, urinary magnesium concentration fell dramatically from 228 to 30 mEq/l within 4 h post-transfer, but 8 h after transfer, U/H (urine/hemolymph) ratios stabilized at between 1.0 and 2.5. Sodium was higher in urine than in hemolymph during the first 24 h after transfer, while potassium was lower in urine than in hemolymph until 72 h after transfer, which suggests that sodium and potassium concentrations are regulated by the antennal gland after an abrupt change in media. In Experiment 2, the urinary production rate of P. monodon decreased as salinity increased, suggesting that the antennal glands also regulate body volume. In the acclimated shrimps of Experiment 2, the antennal glands did not appear to regulate osmolarity or the concentration of chloride, sodium, potassium, and calcium ions, but as salinity increased, U/H ratios of magnesium increased from 2.3 to 13.5, and active secretion by the antennal gland accounted for 57 approximately 93% of the total magnesium excretion through urine. These results suggest that active secretion of magnesium by the antennal gland enable this shrimp to maintain hypoionic levels of magnesium in the hemolymph.

Involvement of the central nervous system in neuroendocrine mediation of osmotic and ionic regulation in the freshwater shrimp Macrobrachium olfersii (Crustacea, Decapoda)

The presence of putative neurofactors within the central nervous system, i.e., the eyestalks (ES), ventral nerve cord (VNC), and supra-esophageal (SEG) and thoracic ganglia (TG), which are involved in osmotic and ionic regulation, was investigated in the euryhaline, freshwater shrimp, Macrobrachium olfersii. Homogenates were prepared from shrimps exposed for 6 hr to a high salinity medium (HSM, 21/1000 S) and were injected into shrimps subsequently maintained for 1, 3, or 6 hr in freshwater (FW, 0/1000 S) or HSM. Osmolality and sodium, chloride, and calcium concentrations were determined in single hemolymph samples removed at each time interval. Heart rates and wet weights were measured before and after experimental treatments. Exposure to HSM increased [Na+] and [Cl-] and heart rate. Injection of ES homogenate increased osmolality, [Na+] and [Cl-], and wet weight in shrimps maintained in FW; VNC homogenate also increased hemolymph [Cl-] in shrimps maintained in FW after injection, but reduced heart rate in shrimps subsequently exposed to HSM. Injection of TG homogenate reduced heart rate to a lesser extent in shrimps maintained in FW. Hemolymph [Ca2+] was not altered by homogenate injection. The exposure period of 6 hr to HSM appears to result in the accumulation of factors within the central nervous system that regulate the osmotic and ionic concentrations of the hemolymph, in addition to exerting antidiuretic and cardio-depressor actions. The coordinated action of these factors is intimately involved in the hyporegulatory processes that permit the survival of M. olfersii in media of elevated salinity.

Neuroendocrine regulation of osmotic and ionic concentrations in the hemolymph of the freshwater shrimp Macrobrachium olfersii (Wiegmann) (Crustacea, Decapoda)

Putative neuroendocrine mediation of osmotic and ionic responses to acute exposure to high salinity medium was investigated in the freshwater shrimp Macrobrachium olfersii (Wiegmann). Homogenates of supra-esophageal or thoracic ganglia, prepared from shrimps exposed to seawater of 21% S for 6 hr, were injected into the abdominal musculature of shrimps previously exposed to freshwater and subsequently exposed to either freshwater or seawater (21% S). Osmotic, sodium, chloride, potassium, magnesium, and calcium concentrations were determined in hemolymph samples removed by intracardiac puncture at time = 0, 1, 3, or 6 hr after homogenate application. Control shrimps were injected with filtered seawater, isosmotic to the hemolymph, and treated similarly. In control shrimps, the osmotic, Na+, Cl-, K+, Mg2+, and Ca2+ concentrations in the hemolymph increased (P less than or equal to 0.05) after 1-hr exposure to seawater. In shrimps injected with homogenates of supra-esophageal ganglion and exposed to seawater, osmotic and ionic concentrations in the hemolymph did not vary with exposure time; in injected shrimps exposed to freshwater, Na+, Cl-, K+, and Mg2+ concentrations decreased (P less than or equal to 0.05) with time. In shrimps injected with homogenates of thoracic ganglion and exposed to seawater, hemolymph osmotic, K+, and Mg2+ concentrations increased (P less than or equal to 0.05); Na+, Cl-, and Ca2+ concentrations remained unchanged. In injected shrimps exposed to freshwater, hemolymph osmotic concentration alone increased (P less than or equal to 0.05) after 1 hr, all other ionic concentrations remaining unchanged. These data suggest that neurofactors apparently located within the ganglia of the central nervous system of M. olfersii may alter the apparent ionic permeabilities of this shrimp, depending on the salinity characteristics of the external medium. The data support the notion that invasion of the freshwater biotope by estuarine crustaceans has necessitated the evolution of specific physiological mechanisms capable of compensating for the osmotic dilution and ion loss typically encountered by such organisms.

Neuroendocrine control of hydromineral regulation in the American lobster Homarus americanus H. Milne-Edwards 1837 (Crustacea, Decapoda). 1. Juveniles

Juvenile lobsters survive well in salinities above 10.2% (300 mOsm/kg), and their osmotic and ionic (Cl-, Na+, Ca2+) regulation in dilute sea water is slightly hyperosmotic, similar to that of adults. Approximately a month after eyestalk ablation, osmotic and ionic (Cl-, Na+) regulation becomes isosmotic, water content increases, and survival rate in dilute sea water declines, but these changes can be partially reversed by implantation of eyestalk neuroendocrine tissue. Regulation of Ca2+, in contrast, is only slightly affected by eyestalk ablation. These results indicate that osmotic regulation and regulation of hemolymph Na+ and Cl- concentrations are at least partly controlled by eyestalk neuroendocrine factors in this species.