Ingestion, absorption, and gonad production of adult Strongylocentrotus franciscanus fed different rations of a prepared diet

Feed costs are a major portion of aquaculture operations. Accurate estimate s of daily ration are vital to prevent overfeeding which results in wasted feed, poor water quality, underfeeding, and reduced growth. Understanding t he relationship of ingestion rate and absorption efficiency of Strongylocen trotus franciscanus should improve the cost effectiveness of aquaculture of this candidate species. Adult S. franciscanus were collected from a subtid al area devoid of algae and fed two rations of an extruded diet for 62 d. M ean test diameter and whole weight of an initial sample were 91 +/- 2 mm an d 295 +/- 18.4 g (mean +/- SEM; N = 16). The two rations used were 1-g dry feed/d or 3 g/d. An unfed control group was also maintained. Eight urchins per treatment showed significant differences in food ingestion rate, total organic absorption, gonad index, gut index, and moisture content of the gon ad (P < 0.001). Food intake was greatest in the high ration treatment, whil e total organic absorption was greatest in the low ration treatment. The go nad index of S. franciscanus in the high food ration was significantly grea ter than the initial gonad index and was also greater than the index of ani mals in the low ration and unfed treatments. The gonad index of animals in the low food ration treatment was significantly greater than the index of t he initial sample and the index of animals in the unfed treatment. The gut index of urchins in the high food ration treatment was significantly greate r than initially and was also greater than the gut index for animals in the low ration and unfed treatments. The gut index for urchins in the unfed tr eatment was significantly less than the initial index. The moisture content of the gonad of urchins fed the prepared diet was significantly greater th an the gonad moisture content of the initial sample or unfed group. Test di ameter, whole animal weight, and gonad production efficiency (increase in g dry gonad weight/g dry feed intake) were not significantly different (P > 0.200). Histological examination of the gonads showed S, franciscanus in th e two ration treatments developed from the spent to the growing ol prematur e stage while the unfed controls lost nutritive tissue and contained only r elict gametes or remained in the spent condition. The results suggest S. fr anciscanus from food-limited environments can he fed appropriate rations to control gonad production.