Fish Hatchery Management - fisheries & aquaculture

HA'|CHERY OPERATIONS6Iratio than a poorly fed one of the same length; it will be in better condition,hence the term condition factor.Each fish species has a characteristic range of condition factors, and thisrange will be small if fish do not change their bodily proportions as theyg.ow (some species do change, but not the commonly cultured ones). Rei_atively slim fish, such as trout, have smaller typical condition factors thando stouter fish such as sunfish.The value for a condition factor varies according to how length is measuredand, 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 projectsfarther forward) to the tip of the tail when the tail is spread normally.when measurements are made in English units (inches and pounds), thesymbol used is c. For metric measurements (millimeters, g.ams), the symbolis -6. The two types of condition values can be converted by the formulac: 36'13f,. In either case, the values are quite small. For example,for one sample of channel catfish, condition factors were c: 2gltt x l0 7(0.0()029ltl) and ,f : tJ0.76 x l0 ;.once c is known, the tables in Appendix I can be used to find lengthweightconversions. The eight tables are organized by increasing values ofc, and representative species are shown for each. Because not all speciesare listed, and because C will vary with strains of the same species as wellas with diet and feeding levels, it is wise to establish the condition factorindependently for each hatchery stock. weigh a sample of 50-100 fishtogether, obtaining a total aggregate weight. Then anesthetize the fish andmeasure their individual lengths. Finally, calculate the average length andweight for the sample, enter the values in the formula c (or K): wl L3,and consult the appropriate table in Appendix I for future lensth-weiehtconversions.Growth RateGrowth will be considered as it relates to production fish, generally thoseless than two years of age. The growth rate of fish depends o., -urry factorssuch 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 determiningrearing space needs, water-flow projections, and production goals. The abilityto project the size of the fish in advance is necessary for determiningfeed orders, egg requirements, and stocking dates. A key principle underlyingsize projections is that well-fed and healthy fish grow at predictablerates determined by water temperature. At a constant temperature, the