HATCHERY OPERATIONS 61 



ratio than a poorly fed one of the same length; it will be in better condi- 

 tion, hence the term condition factor. 



Each fish species has a characteristic range of condition factors, and this 

 range will be small if fish do not change their bodily proportions as they 

 grow (some species do change, but not the commonly cultured ones). Rel- 

 atively slim fish, such as trout, have smaller typical condition factors than 

 do stouter fish such as sunfish. 



The value for a condition factor varies according to how length is meas- 

 ured and, more importantly, according to the units of measurement, 

 English or metric. For purposes of this book, lengths are total lengths, 

 measured from the tip of the snout (or lower jaw, whichever projects 

 farther forward) to the tip of the tail when the tail is spread normally. 

 When measurements are made in English units (inches and pounds), the 

 symbol used is C. For metric measurements (millimeters, grams), the sym- 

 bol is K. The two types of condition values can be converted by the for- 

 mula C = 36.13/r. In either case, the values are quite small. For example, 

 for one sample of channel catfish, condition factors were C = 2918 x 10 ' 

 (0.0002918) and A' = 80.76 x 10"^ 



Once C is known, the tables in Appendix I can be used to find length- 

 weight conversions. The eight tables are organized by increasing values of 

 C, and representative species are shown for each. Because not all species 

 are listed, and because C will vary with strains of the same species as well 

 as with diet and feeding levels, it is wise to establish the condition factor 

 independently for each hatchery stock. Weigh a sample of 50-100 fish 

 together, obtaining a total aggregate weight. Then anesthetize the fish and 

 measure their individual lengths. Finally, calculate the average length and 

 weight for the sample, enter the values in the formula C (or A') = W/L', 

 and consult the appropriate table in Appendix I for future length-weight 

 conversions. 



Growth Rate 



Growth will be considered as it relates to production fish, generally those 

 less than two years of age. The growth rate of fish depends on many factors 

 such as diet, care, strain, species, and, most importantly, the water tem- 

 perature (constant or fluctuating) at which they are held. 



Knowing the potential growth rates of the fish will help in determining 

 rearing space needs, water-flow projections, and production goals. The abil- 

 ity to project the size of the fish in advance is necessary for determining 

 feed orders, egg requirements, and stocking dates. A key principle underly- 

 ing size projections is that well-fed and healthy fish grow at predictable 

 rates determined by water temperature. At a constant temperature, the 



