Flow along the Gut and Intestinal Absorption of Salt and Water in Euryhaline Teleosts: A Theoretical Analysis

1. In euryhaline teleosts the transmural salt and water flow and the flow and concentration changes along the gut were simulated by analogue computation. The purpose was to elucidate the interaction of and sensitivity to the parameters of the system particularly with respect to intestinal water absorption. The simulations were based on data obtained from the yellow European eel, the rainbow trout and the cyprinodont Aphanius dispar.

2. When the experimental values for drinking rate, maximal NaCl absorption rate and concentration at half-maximal absorption rate, osmotic permeability coefficient, solute-linked water flow, and concentrations in the gut were used in the model, good consistency was achieved, and predictions could be made.

3. The simulations demonstrated a close linkage between drinking rate and maximal NaCl absorption rate. A large water absorption was only possible close to an optimal drinking rate for each value of maximal NaCl transport rate. The water absorption was little sensitive to the osmotic permeability coefficient of the intestinal wall.

4. As a means of adaptation to waters of high salinity an increase in maximal NaCl absorption rate was shown to be very costly for energetic reasons. This supports indirectly the concept that the osmotic permeability of the gills must go down. The increase in plasma osmolality was a useful part of the adaptation.

Observations on strigeid metacercariae in the eyes of fish from Hanningfield Reservoir, Essex, England

A comparative study was made of the occurrence of the metacercariae of Diplostomum spathaceum, Tylodelphys clavata and T. podicipina in the eyes of brown and rainbow trout, perch, ruffe, roach, ten-spined stickleback, eel and stone-loach, from Hanningfield Reservoir, Essex between January 1968 and March 1969. D. spathaceum was found in all fish species and T. clavata in all except eel and stone-loach. The degree of infection varied considerably between different host species. T. podicipina occurred mainly in young perch but was also found in rainbow trout and ruffe. D. spathaceum normally occurring in the lens was also found in considerable numbers in the humor of the eye in brown and rainbow trout, perch and ruffe. Infection with D. spathaceum and T. clavata increased with length and age of the host although in some host species there was a reduction in the largest fish examined. Newly introduced rainbow trout became infected with D. spathaceum and T. clavata during their first summer in the reservoir.

Immunofluorescent cell assay of infectious pancreatic necrosis virus

An immunofluorescent cell (IFC) assay technique was developed for the quantification of infectious pancreatic necrosis (IPN) virus of salmonid fishes. Cover slip cultures of rainbow trout gonad (RTG-2) cells were infected with diluted virus preparations. After incubation to permit antigen development, the cells were stained with antiviral fluorescent antibody, and the number of fluorescing (infected) cells was counted. Optimal conditions for the IFC assay procedure are: (i) the use of RTG-2 cells cultured for at least 3 days at 20 C; (ii) 1-h absorption of IPN virus to RTG-2 cells at 20 C or alternatively, 4 h at 4 C; (iii) staining the infected cell cultures at 10 to 12 h postinfection. A linear relationship between the relative concentration of virus in the inoculum and the number of fluorescent cells in the first cycle of infection was observed. The IFC assay method is more sensitive than the plaque method for the assay of IPN virus.