CHANGES IN SERUM CONCENTRATIONS OF CHANNEL CATFISH (ICTALURUS-PUNCTATUS RAFINESQUE) PHOSPHORYLCHOLINE-REACTIVE PROTEIN (PRP) IN RESPONSE TOINFLAMMATORY AGENTS, LOW-TEMPERATURE-SHOCK AND INFECTION BY THE FUNGUS SAPROLEGNIA SP

Channel catfish (Ictalurus punctatus Rafinesque) produce a 100-kDa ser um protein referred to as phosphorylcholine-reactive protein (PRP). PR P appears homologous to human C-reactive protein (CRP) i.e. it is an a cute phase pentraxin with calcium-dependent reactivity with phosphoryl choline. In this study a immunoassay was employed to quantify PRP leve ls in sera of pond-raised catfish collected at monthly intervals (Janu ary 1990 to January 1992) from ponds in Mississippi. Serum PRP was als o measured in laboratory-maintained catfish exposed to physical, envir onmental, or chemical stressors and for catfish infected with the fung us Saprolegnia sp. For pond-raised catfish the average level of serum PRP was 2.42 +/- 0.85 mg ml-1 for healthy animals and 1.74 +/- 0.94 mg ml-1 for those infected with Saprolegnia sp. In general PRP levels we re maximal in summer and minimal in winter, coincident with similar ex tremes in pond-water temperature. Levels of serum PRP for laboratory-m aintained catfish were higher and more variable (3.8 +/- 2.4 mg ml-1) than those for pond-raised fish. Within 2-4 days after injection with turpentine, serum PRP levels in laboratory-maintained catfish rose to concentrations as high as 10.6 mg ml-1, representing an 18-fold increa se over pre-injection levels. In contrast, fish injected with pneumoco ccal C-polysaccharide or Saprolegnia sp. fungal homogenate exhibited t ransient decreases in serum PRP levels. Concentrations of serum PRP fo r catfish subjected to low temperature-shock decreased 14% compared to pre-shock values by day 6 and 86% by day 18. In contrast, by day 6 fi sh subjected to low temperature-shock and subsequently infected with S aprolegnia sp. exhibited PRP levels 57% lower than healthy fish and 50 % lower than healthy, low temperature-shocked fish. Several lines of e vidence suggest that reduced levels of serum PRP induced by low temper atures may play a major role(s) in determining the increased susceptib ility of channel catfish to infection by Saprolegnia sp. during the wi nter months.