Somatic and gonadal growth of the sea urchin Psammechinus miliaris (Gmelin) fed artificial salmon feed compared with a macroalgal diet

The effect on somatic growth of a commercially manufactured diet (salmon fe ed) compared to a macroalgal diet (Ulva lactuca or Laminaria saccharina) wa s studied for three stages in the Life history of the green sea urchin, Psa mmechinus miliaris (Gmelin). Three size classes were studied; 0.89 to 1.1 m m, 15.3 to 15.8 mm and 21.3 to 21.7 mm. The effect on gonadal growth of the salmon feed compared to a macroalgae diet (L. saccharina) was also studied . A significant difference was observed in the somatic growth in the two la rgest size classes, with the sea urchins fed salmon feed exhibiting the hig hest growth rates. In the smallest size class however, there was no differe nce in the test diameter of the urchins fed the salmon feed and macroalgae at the end of the trial, although both had a significantly greater test dia meter than the "unfed" control group. A significant increase was also seen in the gonadal index (GI) of the urchins fed salmon feed compared with the macroalgal diet. This growth was extremely rapid, with an increase in GI fr om 3.7% to 27.5% in 4 weeks, and there was no postspawning decrease in the GI observed. The experiments highlight the resource partitioning between so matic and gonadal production throughout the Life history of P. miliaris in response to diet quality. The elevated production observed in P. miliaris f ed the manufactured diet also suggests that this could be used as a basis f or the development of a more refined diet for this potential aquaculture sp ecies.