Estimation of live standard length for winter flounder Pleuronectes americanus larvae from formalin-preserved, ethanol-preserved and frozen specimens

Abstract

Changes in standard length of laboratory-reared winter flounder Pleuronectes americanus Walbaum larvae, due to preservation in 2 % fonnalin, 95 46 ethanol and frozen at -70 "C in seawater, were studied in larvae ranging from 3.0 to 8.5 mm long. Shrinkage is significant in all media except for larvae > 5 mm preserved in ethanol. The amount of shrinkage is related to size, longer larvae generally shrinking proportionally less than shorter larvae. Shrinkage is highest in 2 %, formalin, intermediate in -70 "C seawater and lowest in 95 % ethanol. Linear regressions of preserved standard length (L,) on live standard length (h) for all 3 preservation methods are: L, = -0.20 + 0.92 (rZ = 0.99, n = 102), L, = -0.43 + 1.06 L, (r2 = 0.98, n = 116), and L, = -0.15 + 0.954, (r2 = 0.99, n = 112) for formalin, ethanol and freezing, respectively. The relationships cdn be used to obta~n an estimator of live length of laboratory-reared winter flounder larvae and are approximat~ons of llve length of field-collected larvae. A nonlinear multiple regression of percent shrinkage (S) due to formalin preservation as a function of live length (Lo [mm]) and logarithm of preservation duration (D) in days is calculated for our data and for published studies of other species where shrinkage is reported as a function of live length: S = ll.22e'-0~063 L+0'G71M (r' = 0.79, n = 32). Live length (Lo) as a function of preserved length (L,) and duration of preservation is: = 0.13 + 1 . 0 3 4 + 0.07 D (r2 = 0.99, n = 32). This relationship can be used to predict live length from formalin-preserved larvae in species where size-related shrinkage is unknown.