SCHOLNICK, D. A.*; BURNETT, K. G.; BURNETT, L. E.; Eckerd College, St. Petersburg, Fl; Grice Marine Lab, College of Charleston, SC: Impact of Bacterial Infection on Respiratory Function in the Penaeid Shrimp Litopenaeus vannamei
Following injection into muscle or hemolymph, bacterial pathogens rapidly localize to crustacean gills and hepatopancreas, while the number of circulating hemocytes declines. Subsequent aggregation of hemocytes and bacteria may lead to the formation of nodules at the gill. We hypothesized that aggregation of bacteria and hemocytes at the gill, impairs normal hemolymph flow and thereby limits oxygen diffusion. The rate of oxygen uptake (MO2) was determined for the penaeid shrimp Litopenaeus vannamei following injection with the pathogenic bacteria Vibrio campbellii (105/g) for the first 4 h and after 24 h following infection. Injection of bacteria decreased shrimp MO2 over 30% (from 12.1 to 8.2 �mol g-1 h-1) after 4 h when compared to saline-injected shrimp. Decreased MO2 persisted after 24 h post-Vibrio injection (3.3 �mol g-1 h-1 lower than controls). In well-aerated water, whole animal lactic acid levels were 1.7 times higher at 4 and 24 h in shrimp injected with bacteria, compared to saline-injected shrimp. In order to determine if low environmental oxygen would further limit diffusion and increase anaerobic metabolism, shrimp were exposed to hypercapnic hypoxia (HH; PCO2 = 2 kPa, PO2 = 6.7 kPa; above critical PO2). HH exposure following Vibrio injection resulted in a two fold increase in lactic acid (4.0 �mol g-1 tissue) compared to saline-injected shrimp (1.8 mol g-1 tissue). Injection of bacteria had no influence on hemocyanin or hemolymph protein concentrations when compared to saline injection. These results support the hypothesis that aggregation of hemocytes in the gills impairs normal respiratory function and help explain the increased susceptibility of crustaceans to infectious disease in hypoxic environments. Supported by NSF IBN-0212921 to KGB and LEB.
