Sevigny et al,: Identification and distribution of larvae or Sebastes fasaatus and 5, mentella 



377 



52° 



Abundance (ind./m-) 

 • < I + no lanac 



Belle Isle Striiil 



50° 



48° 



46° 



Figure 1 



Geographic distribution and abundance of redfish larvae at stations sampled in June- 

 July 1991 in the Gulf of St. Lawrence. 



and for genotype determination. This procedure was 

 adopted to minimize possible bias towards selection 

 of larger larvae during sorting. A maximum of 10 

 larvae were placed on each plate. The total number 

 of larvae so treated varied between stations owing 

 to variable larval abundance at each station. The 

 remaining sample with unsorted larvae and plankton 

 was preserved in a \0'7( formalin seawater solution 

 (4'7f foiTnaldehyde) for subsequent laboratory sorting. 

 Re-examination of the samples and subsamples in 

 the laboratory showed that the proportion of larvae 

 remaining in the samples was always less than 51 

 and that in most cases, larvae had been effectively 

 sorted during the initial onboard sorting process. 



The larvae placed on plates were individually video- 

 recorded with a Hitachi black and white camera 

 mounted on a stereomicroscope at 6x and 9x magni- 

 fication and connected to a Sony Beta videotape 

 recording machine. Periodic calibration of the magni- 

 fication was made by filming a stage micrometer. 

 The overall procedure (from sorting to filming) was 

 completed in less than 5 min. and care was taken to 

 ensure that larvae were alive during the video recor- 

 ding. The fish were sorted and video-taped on board 

 while still alive so that morphometric measurements 



represented real values; these fish were later used 

 for genetic analyses. This procedure eliminated the 

 necessity of having one subsample for morphometric 

 analyses and another one for biochemical analyses 

 and did not introduce any measurement bias due 

 to postmortem and preservation shrinkage (Magniis- 

 son^). Afterwards, each plate with larvae was immer- 

 sed for a few seconds in liquid nitrogen, then placed 

 in a petri dish and stored on board at -40 'C. Samples 

 were transferred to a -80°C freezer in the laboratory 

 until electrophoresis analyses were carried out. 



Laboratory analyses 



Standard lengths of individual larvae was measu- 

 red from the video recordings that were digitized 

 with a Bioquant M8 image analyzing system. Repea- 

 ted measurements of individual larvae indicated a 

 measurement error of less than 3% (de Lafontaine, 

 unpubl. data). Plankton samples were examined com- 

 pletely and the redfish larvae were sorted and enu- 



Magniisson, J, V. 1982. Shrinkage of dying redfi.sh larvae. 

 Counc. Explor. Sea (ICES) Council Meeting 1982/G:23. 



Int. 



