58 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 27. A proposed method to archive the early life history stages of fishes. In the left foreground is a series of three vials, the first contains 

 the specimens and preservation fluid and is capped with a polyseal closure. This first vial is placed into the second with the documentation. The 

 third vial is a complete unit. As evaporation occurs the outer vial pops free of its plastic closure, indicating that the vial requires curatorial 

 attention. The vials can be placed together in commercially available paper trays, which can be arranged in commercially available wooden trays 

 much like entomological collections are maintained. 



these chemicals and prevent us from standardizing a protocol 

 are not biological ones but rather those of chemistry. 



Fixatives. — Formahn generally is accepted as the most appro- 

 priate fixative. However, it must be used in a specific concen- 

 tration, polymerizes with age and with contact with metals, and 

 is a poison. Tucker and Chester (in press) found that formalin 

 used with salt water causes significant shrinkage, whereas an 

 unbuffered 4% solution of formalin mixed with freshwater caused 

 the least amount of shrinkage and distortion during fixation. 

 They found that pigment preserves best in a solution of un- 

 buffered freshwater formalin. Although the pigment holds up 

 well in this solution, the skeleton decalcifies and reduces or may 

 even prevent staining for either bone or cartilage using the meth- 

 ods of Dingerkus and Uhler (1977). In the absence of a suitable, 



inexpensive substitute we recommend that formalin be used for 

 fixing zooplankton samples, using the standard ichthyoplankton 

 protocols described by Smith and Richardson (1977). This pro- 

 tocol could be modified so as to use freshwater rather than 

 seawater in preserving the sample (Smith and Richardson, 1977: 

 16-section 2.1.3.1) so as to reduce shrinkage. 



Buffers— The problems associated with buffers are more diffi- 

 cult to unravel. Buffers have been used in an attempt to control 

 fluctuating pH during fixation and preservation. Buffers are 

 needed to prevent a reduced pH in either the fixative or pres- 

 ervation solution to avoid excessive acidity in formalin that 

 may decalcify bone (Taylor, 1 977). However, tissues clear when 

 the buffer makes the solution alkaline. Taylor's (1977) data 

 indicate that pH can fluctuate only in a narrow range without 



