Effect of binder type and concentration on prepared feed stability and gonad yield and quality of the green sea urchin, Strongylocentrotus droebachiensis

Adult green sea urchins, collected from the wild, were held in laboratory tanks and fed one of eight prepared feeds--varying solely in the type and concentration of binder used in the diet (i.e. gelatin, guar gum, sodium alginate, or corn starch each being present at 3% or 5% dry weight)--for a period of 12 weeks. Two control treatments, kelp and a commercially available salmon feed, were also included. Gonad colour, percent gonad water, and percent gonad yield of urchins in the 10 feeding treatments were determined approximately every week while gonad texture, firmness, and taste were subjectively evaluated at the end of the experiment. Results were contrasted with those of wild specimens collected from the source population at weeks 0, 4, and 12 of the experiment. Pellet coherence and amount of deed lost were examined in separate feed stability trials. After 12 weeks, all prepared feeds produced significantly higher percent gonad yields than kelp or wild controls. Binder type significantly affected percent gonad yield at week 9, the highest yield being attributed to feeds made with gelatin. By week 12, however, there were no significant differences in percent gonad yield among the different binders and this was attributed to yields reaching a physiological maximum. Binder concentration significantly affected percent gonad yield at the end of the experiment with the higher concentration producing greater yields. While gonad colour was significantly affected by binder type (starch producing better colour than any other binder), all prepared feeds generally produced gonads that were cream or tan in colour. This contrasted with kelp-fed or wild controls that typically had pale yellow or orange gonads. Binder significantly affect gonad colour. While the texture of gonads from urchins fed prepared feeds was statistically similar to that of gonads taken from kelp-fed or wild individuals, firmness and taste were significantly poorer. Binder concentration did not significantly affect gonad texture, firmness, or taste. Feed stability was significantly affected by binder type (gelatin producing more stable pellets than any other binder), but not concentration. Amount of feed lost from pellets was not significantly affected by binder type or concentration, but this was most probably due to the fact that flow rates in the tanks were not sufficient to wash broken feed out of experimental units. Based on these results, gelatin is the binder recommended for use in further dietary experiments and commercial-scale feed operations.