The sinergetic effect of temperature and salinity on Rotifer Branchionus plicatilis (O. F. MÜLLER) population growth and lorica size in mass rearing

Abstract

         The synergetic effect of temperature (22, 27,35 ^oC) and salinity (20, 27,38 psu) on population growth and changes in lorica length and width of the rotifer Brachionus plicatilis was investigated under mass rearing conditions. The greatest average population density (432.4 ind. ml^-1) and the fastest doubling time (D=17.2) was noted at a salinity of 20 psu and at 22^oC. Daily harvesting 50-60% of the contents of one 400 l volume tank, satisfied the food intake of 0.5-0.6x10⁶ reared fish larvae. Various salinity and temperature combinations resulted in significantly different lorica sizes (ANOVA, P<0.001). This shows that it is possible to produce rotifers with the required lorica size, depending on the functional mouth gape of larvae. Differences noted in the growth rates of rotifer numbers and the variety in lorica size in mass rearing conditions was attributed to the phenomena of cyclomorphosis, stimulated by the synergetic effect of salinity and temperature. This is confirmed by the increase in lorica dimensions after equalizing conditions in the experimental tanks with those in the brood stock.