An evaluation of back-calculation methodology using simulated otolith data

I simulated somatic growth and accompanying otolith growth using an individual-based bioenergetics model in order to examine the performance of several back-calculation methods. Four shapes of otolith radius-total length relations (OR-TL) were simulated. Ten different back-calculation equations, two different regression models of radius length, and two schemes of annulus selection were examined for a total of 20 different methods to estimate size at age from simulated data sets of length and annulus measurements. The accuracy of each of the twenty methods was evaluated by comparing the back-calculated length-at-age and the true length-at-age. The best back-calculation technique was directly related to how well the OR-TL model fitted. When the OR-TL was sigmoid shaped and all annuli were used, employing a least squares linear regression coupled with a log-transformed Lee back-calculation equation (y-intercept corrected) resulted in the least error; when only the last annulus was used, employing a direct proportionality back-calculation equation resulted in the least error. When the OR-TL was linear, employing a functional regression coupled with the Lee back-calculation equation resulted in the least error when all annuli were used, and also when only the last annulus was used. If the OR-TL was exponentially shaped, direct substitution into the fitted quadratic equation resulted in the least error when all annuli were used, and when only the last annulus was used. Finally, an asymptotically shaped OR-TL was best modeled by the individually corrected Weibull cumulative distribution function when all annuli were used, and when only the last annulus was used.

Monoculture of marine planktonic diatoms and the effects of different media on their growth and survival

Diatoms are the preferred live food of the protozoea stages of prawns. Due to seasonal variations, it is difficult to obtain continuous supply of diatoms and other algae throughout the year. Therefore mass culture of diatoms is necessary. At attempt was made to culture planktonic diatoms and to study the effect of Allen and Nelson media, Simon media, Vitamin B12 and treated sewage water media on their growth and survival. Navicula sp showed better growth in Allen and Nelson media, Coscinodiscus and Chaetoceros grew better in Simon media while Navicula sp and Coscinodiscus sp showed better growth in the combination of Allen and Nelson + Vitamin B12.