Growth of the rabbitfish Siganus randalli Woodland - University of ...

CONTROLLED GROWTH TRIALSInitial growth trials were conducted in tanks at the Guam Aquaculture Developmentand Training Center. These trials allowed an accurate determination of feed conversionratios, and also allowed us to conduct replicated trials to investigate several factors that mightinfluence the growth of juvenile siganids. The replicated trials included: I) comparison oftwo commercial fish feeds with respect to growth, 2) comparison of three feeding rates withrespect to growth and apparent feed conversion ratio, and 3) comparison of three feedingfrequencies with respect to growth.MATERIALS AND METHODSComparison of dietsWe conducted growth trials in tanks to compare two diets currently in use onaquaculture farms and at the Guam Aquaculture Development and Training Center. The dietlower in protein (36% crude protein) was formulated for catfish and is used by commercialproducers and for maintenance of our siganid broodstock; the other diet (55% crude protein)was formulated for salmon ids and has been used in the production and rearing of juvenilesiganids at the hatchery. The composition of the diets is shown in Table 2. Each growth trialwas conducted in a set of six 2-ton, flow-through tanks supplied with seawater at a rate of 5tank-volumes per day.Two growth trials were conducted to determine the effect of diet on siganid growthrates. For the initial trial, we stocked each tank with 50 juvenile siganids. We planned thisexperiment to provide information on the variation in growth between fish from this type ofexperimental design; therefore, a large sample size was used. We randomly assigned each ofthe six tanks to one of the treatments. The ranges of dissolved °2 , pH, and temperature overthe duration of the initial growth trial are presented in Table 3. The weight and standardlength of each fish was taken immediately before the experiment. The fish were fed at 9% ofthe initial total weight of the individuals, with the feed divided into two or three feedings perday. After 21 days, the weight and length of each fish was again determined.The initial trial was compromised somewhat by mortalities that occurred in three ofthe tanks on the second day of the trial. These mortalities were attributed to handling stress.As a result, we repeated the comparison, this time with fewer (10) fish per tank and an excessof feed.We used the BMDP package of statistical programs (BMDP Statistical Software, Inc.,Los Angeles, California) for all analyses. The experimental design was that of a nestedanalysis of variance with fish nested in tank and tank nested in diet. The sample sizes pertank were large enough to allow the use of a one-way ANOVA followed by a Student­Newman-Keuls test to examine differences between tanks.