RAPID METHOD FOR DETERMINING WATER CONTENT IN OYSTER TISSUE 



By Thomas C. Carver, Jr., Fishery Biologist (Research) 1 

 Bureau of Commercial Fisheries Biological Laboratory, Oxford, Md. 



Medcof (1941) defined Condition Index (CI) 

 as the ratio of the dry weight of the meat to the 

 volume of the space between the valves X 1000. 

 To dry the meat, Engle (1958) used 72 hours ex- 

 posure at 90° C. in a convection-type oven. This 

 will reduce a 25 g. sample to constant weight ; how- 

 ever, it is frequently desirable to avoid the 72-hour 

 waiting period. 



Korringa (1956) reported a method by which 

 the water content of oyster meats could be deter- 

 mined volumetrically using toluene distillation. 

 The homogenized sample was placed in a flask and 

 covered with toluene. The flask was connected to 

 a condenser fitted with a distillation trap and main- 

 tained at 100° C. for 1 hour. The volume of water 

 collected was measured and converted to weight. 

 The total time required was about 1 hour. We 

 were unable to get the reproducible accuracy de- 

 sired because of the tenacity with which small 

 droplets of water adhered to the sides of the con- 

 denser and fittings. To overcome this problem we 

 devised a gravimetric adaptation of Korringa's 

 method which eliminates the condenser and its as- 

 sociated problems and in which the weight of water 

 is determined directly. This adaptation is dis- 

 cussed below. 



Figure 1 shows all major components of the ap- 

 paratus. The function of the intake drying 



NOrB. — Approved for publication April 13, 1965. 



1 The present address of Thomas C. Carver, Jr., is Pesticide 

 Registration Review Staff, Patuxent Wildlife Research Center, 

 Laurel, Md. 



tubes is to provide an atmosphere free of moisture. 

 A 10 g. sample of homogenized oyster tissue is 

 covered with toluene and heated to 100° C. for 45 

 minutes. The water vapor is collected in the tared 

 outlet drying tubes. All tubes contain the drying 

 agent, calcium chloride. Plastic check valves con- 

 trol direction of water vapor flow. The number of 

 drying tubes needed can be determined by a trial 

 run in which weights of the individual tubes are 

 recorded. The last tube in direction of flow on 

 both sides of the flask should not show a weight 

 increase. In practice, once the proper number of 

 tubes is determined, the tubes can be weighed as 

 a unit. Suction should be applied very gently. 

 With this method, we have been able to produce the 

 same accuracy in 45 minutes that requires 72 hours 

 in a conventional drying oven. 



LITERATURE CITED 



Engle, James B. 



1958. The seasonal significance of total solids of 

 oysters in commercial exploitation. Proc. Nat. 

 Shellfish. Ass. 48 : 72-78. 

 Korringa, P. 



1955. Qualitatsbestimmungen an Miesmuseheln und 

 Austern. Arch, Fischereiwiss, 6 : 189-193. ( Trans- 

 lation by N. M. Carter. 1956. Quality determina- 

 tions of mussels (Mytilus edulis) and oysters. 

 Fish. Res. B. Can., Transl. Ser. 76.) 

 Medcof, J. C. 



1941. The influence of temperature and salinity on 

 the condition of oysters (Ostrea virginicus). J. 

 Fish. Res. B. Can. 3: 253-257. 



FISHERY BULLETIN: VOLUME 65, NO. 3 



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