Young sand-shrimps having an initial weight of 63 mg were reared for 4 months with a natural diet (A) and a compounded diet (B). 2. Growth is studied, both by the evolution of the fresh weight and the variation of cell-number and cell-size; these are estimated from total DNA and fresh-weight/DNA ratio evolution. 3. With diet A, the mean weight increment is a linear function of time, the daily weight-gain being equal to 2.8 mg/day. The increase in total DNA content per shrimp is a linear function of fresh weight; its value goes up from 187 to 1020 micromoles. The fresh-weight/DNA ratio, initially equal to 337.9 (mg/micromoles) ,remains constant. For the whole experiment, growth is only a result of cellular multiplication. 4. With diet B, the weight gain is inferior to that observed with diet A. The fresh weight gain curves show two visibly homogenous steps, each with a distinct growth-rate; the mean daily weight gain is equal to 1.7 mg/day during the first two months, and equal to 2.6 mg/day for the two following months (fig. 1). In reality, from the total DNA and fresh-weight/DNA ratio evolution, 3 successive steps can be discerned (fig. 2, fig. 3). During the first month, total DNA increases from 187 to 418 micromoles and fresh-weight/DNA ratio falls down to 273.9, a-19% decrease. For this period, growth is only the result of cellular multiplication, and the decrease of the weight-gain in comparison with diet A is attributed to a decrease in cellular size. During the second month, as the fresh weight increases from 114.5 to 161.2 mg, total DNA increases from 418 to 519 micromoles and the fresh-weight/DNA ratio returns to its initial value. Two thirds of the growth is the result of cellular multiplication, and the rest being due to cell-size enlarging. For the last two months, as the mean fresh weight increases from 161.2 to 296.7 mg, the DNA per shrimp, hence the cell-number, remains constant; but the fresh weight/DNA ratio, or the cell-size, is multiplied by 1.93. 5. By the method used for this study, it is possible to evidence influence of diet on the growth mechanisms themselves (cellular multiplication and cell enlarging). 6. The influence of diet on the growth of the shrimp could be explained by, either a diet qualitative deficiency, or a food-intake decrease. The possibility of a hormonal control has been suggested.
