Effect of urchin size and diet on gonad yield and quality in the green sea urchin ( Strongylocentrotus droebachiensis)

Abstract

A 6-week experiment (August 10 to September 21, 1999) was conducted to determine the effect of urchin size and diet on gonad enhancement of the green sea urchin Strongylocentrotus droebachiensis. Sea urchins were collected from the wild and divided into four size classes—30.0–39.9, 40.0–49.9, 50.0–59.9, and 60.0–73.0 mm test diameter—each size group being split into two dietary treatments [prepared feed or kelp ( Laminaria longicruris and/or Laminaria digitata)]. The experiment was a 4×2 completely crossed design. A number of gonad attributes were quantified at the beginning and end of the experiment including: wet weight, percent yield, percent water, colour, texture, firmness, and taste. The percent change of these variables over the 6-week period was calculated. Colour was assessed subjectively by eye using colour ratings and objectively with a reflected-light, fibre-optic spectrophotometer to generate CIE L* (lightness), a* (hue), and b* (chroma) values. Gonad taste was subjectively evaluated at the end of the experiment. Results from experimental sea urchins were compared and contrasted with those of wild specimens collected from the source population at the end of the experiment. Percent gonad yield at the end of the experiment and percent increase in percent gonad yield over the 6-week period was significantly greater in urchins fed the prepared diet than in those fed kelp. Percent gonad yield was highest in the 40.0–49.9 mm group, followed closely by the 50.0–59.9 and 30.0–39.9 mm size groups, whereas percent increase in percent gonad yield decreased with increasing urchin size. Gonad colour at the end of the experiment was significantly better in urchins fed the prepared diet than in those fed kelp (as judged by colour ratings, a*, and b*) and was better in smaller than larger individuals (as judged by colour ratings, L*, and a*). Percent change in gonad colour ratings decreased and percent change in L* and a* increased with increasing urchin size. Urchin size and feed type had no significant effect on gonad texture, but both factors significantly influenced gonad firmness and taste. Gonads of urchins fed the prepared diet were significantly softer and had significantly more water than those fed kelp. Gonad firmness and percent change in firmness increased with increasing urchin size. Kelp-fed individuals produced significantly better tasting gonads than those fed the prepared diet. The largest urchins produced the best tasting gonads of those fed kelp, but the smallest individuals had the best gonad taste of those fed the prepared diet. Overall, considering both gonad quantity and quality factors, sea urchins of 40.0–49.9 mm test size were deemed to be the most promising for gonad enhancement operations.