An alternative method for the preservation of tropical fish larvae

Abstract

[Extract] Studies of larval processes often aim to explore a link between larval attributes associated with body condition or performance, food availability and larval abundance (Theilacker et al., 1996; Bailey & Picquelle, 2002). Many of these studies involve the comparison of morphological traits, such as fish length and yolk-sac volume to otolith-derived characters, such as daily patterns of growth or fluctuating asymmetry, in an attempt to explore the mechanisms underlying population regulation (Hare & Cowen, 1994; Somarakis et al., 1997; Groenkjaer & Schytte, 1999; Gronkjaer & Sand, 2003). To minimize post mortem degeneration, samples are usually preserved immediately upon capture. Aldehydes, such as formaldehyde solutions (formalin) and gluteraldehyde are effective for fixing and preserving body tissues for future examination, because they form stable cross-links with tissue molecules, thereby stopping metabolic processes (Kirkeby & Moe, 1968). They dissolve skeletal structures, however, including otoliths, preventing subsequent age and growth analyses. Because otolith breakdown is mainly due to the low pH often present in aldehyde solution (Steedman, 1976), the addition of a buffering agent such as simple borax or sodium carbonate can be used to keep the preserving solution nearly neutral or slightly basic, at least temporarily, and slow down the de-calcification process (Hay, 1981). If the solution is correctly buffered, it may be possible to use otoliths from specimens preserved in aldehydes (Suthers et al., 1992; Kristoffersen & Gro Vea Salvanes, 1998). Preservation in buffered acid fixative such as formalin can be problematic, however, as many widely-used buffers damage larvae or ultimately allow the solution to become acid (Lavenberg et al., 1984; Leis & McGrouther, 1994). Therefore, alcohol solutions such as 70 or 95% ethanol are most widely chosen as preservative for otoliths and other bones because they do not decalcify these structures. Unfortunately, they are unsuitable for stabilizing protein constituents and preventing degradation of the animal tissue. Further, both preservative methods cause significant and dissimilar shrinkage (Hay, 1982; Tucker & Chester, 1984; Kruse & Dalley, 1990; Hjo¨ rleifsson & Klein-Macphee, 1992; Kristoffersen & Gro Vea Salvanes, 1998; Fey, 1999), leading to biased estimates of trait distributions and their interrelationships if appropriate corrections are not made.