Ultrastructural changes in hepatopancreatic cells of the prawn

Accumulation of cadmium in the hepatopancreas of the common prawn Palaemon serratus (Pennant) and ultrastructural changes m hepatopancreatic cells were examined after exposure to 3 cadmium concentrations (5, 25.50 ppm) for 44 h. Accumulation of cadmium Ions in 50 ppm solution was 800 % higher compared with control specimens. Absorptive and fibrillar cells (Rand F-cells) in the hepatopancreas were affected by cadmium ions at the ultrastructural 1evel.The ultrastructural changes observed suggest impairment of ion transport, absorption and proteln synthesis. The crustacean hepatopancreas funcbons in food absorption, secretion of digestive enzymes and storage of lipid material (Vonk 1960, Steeves 1969). Ultrastructural studies confirmed results of early light microscope research and related morphological features with the cell's function (Donadey 1969, Loizzi 1971). From these studies it has been established that in the hepatopancreas of Decapoda 4 types of cells are present: E-cells (embryonic cells), R-cells (absorptive cells), F-cells (fibrillar cells) and B-cells (secretory cells) (Davis & Burnett 1964, Bunt 1968, Stanier et al. 1968, Gibson & Barker 1979). There were conflicting results, however, regarding the origin of these cells which depends on the animal's state of nutrition (Stanier et al. 1968). Papathanassiou & K n g (1984) studied the effects of starvation on the fine structure of the hepatopancreas of Palaemon serratus (Pennant), an ecologically important species in British waters. Accumulation of cadmium ions by the crustacean's hepatopancreas under natural and experimental conditions have been studied by several authors (O'Hara 1973b, Hutcheson 1974). Nimmo et al. (1977) studied the effects of cadmium in the shrimp Penaeus duorarum Bukenroad, Palaemonetes pugio Holthius Present address: National Center for Marine Research, Agios Kosmas, GR-166 04 Hellinikon. Athens, Greece and Palaemon vulgaris L. They found significant accumulation of cadmium by the hepatopancreas of controls after 96 h. The rate of uptake in the hepatopancreas was considerably higher than in the gills in the 3 species, and these values for both tissues increased in relation to the concentration. The present study examines the ultrastructural changes in the cells of hepatopancreas of Palaemon serratus and the accumulation of cadmium ions in the tissue of specimens exposed to acutely toxic Cd concentrations. MATERIALS AND METHODS Specimens of Palaemon serratus (Pennant) were collected at Mumbles Point, Swansea, U. K . , at low tide, and kept alive in circulating seawater for 1 wk before use. After this acclimation period, groups of 20 active individuals were placed in crystallizing dishes containing 1 1 of 30 ppt artificial seawater at 15 'C. Screening tests showed that the cadmium concentrations, added as CdCI2.2%H20, causing morphological effects on the hepatopancreas of P. serratus varied between 5 and 50 ppm. Thus the specimens were placed in 3 cadmium concentrations viz. 5, 25 and 50 ppm. These concentrations were determined before starting the experiments using an Atomic Absorption Spectrophotometer. The maximum 1.5 % vanation O Inter-ResearchIPrinted in F. R. Germany 4 0 Dis. aquat. Org. 2: 39-47, 1986 observed was considered to be insianificant. A fourth Table 1. Palaemon serratus. Mean values of accumulated ., group of 20 active was placed in clean 30 cadmium concentrations (dry weight) in the hepatopancreas after 44 h of Cd exposure. Values in parentheses represent % ppt seawater as controls. The seawater was made up by of increase over controls dissolving 'Tropical Marine' salts (Shirley Aquatics Ltd., Solihull, England) in glass-distilled water. Observations were camed out every 6 h and dead individuals were removed. Solutions were renewed after the first 24 h. After 44 h, which is the lethal time for 50 % of the individuals placed in 50 pprn cadmium at 15 "C (Papathanassiou 1984), a number of groups of 10 Live individuals were removed from each concentration including controls. The hepatopancreas was dissected from each individual of each group and dried at 105 "C for 24 h. These tissue samples were then weighed (dry weight 0.30 k 0.02 g) to the nearest 0.1 mg and digested in 5 : l nitric: perchloric acid at 120 "C. Four replicates were used for each concentration and the accumulation of cadmium was determined using a Corning-Eel 240 Mark I1 Atomic Absorption Spectrophotometer. For electron microscopy the hepatopancreas from at least 8 specimens of each group was fixed for 1 h in 5 % cacodylate buffered glutaraldehyde with sucrose added at 0 to 4 "C. It was then washed in several changes of buffered sodium cacodylate with sucrose added, followed by post-fixation in 1 % osmium tetroxide solution for 1 h at 0 to 4 "C. After dehydrabon in graded cold acetone the material was embedded in TAAB embedding resin. Sections with gold or silver interference colours were obtained using a Huxley Mark I Ultramicrotome and were mounted on coated copper grids. They were then double stained in 30 % uranyl acetate (30 min) followed by lead citrate (10 min) and viewed in a Corinth AEI Electron Microscope. The hepatopancreatic cells examined were from every part of the tubule and more than 90 % showed the characteristics that are described in the results.