The Effect of Fixation, Preservation and Freezing on Certain Body Proportions of Two Small Pelagic Fish Species, Sardinella Longiceps (Family: Clupeidae) and Selaroides Leptolepis Collected From Muscat Waters, Sultanate of Oman - page 8

 

The main changes in the three morphological characters used in this study were significant increase. These results agree with the those of Lux (1960), Parker (1963), Burgner (1962), Stobo (1972), Al-Hassan and Abdullah (1992), Al-Hassan and Al-Shawafi (1997), Al-Hassan et al., (2000), Jawad et al. (2001a,b), and Jawad (2003). The no effect and increase criteria in the three fish body proportions of S. leptolepis are interesting features of the present study. Every other study has reported some shrinkage with fixatives and preservatives. In these cases it would appear that the fixation, preservation and freezing techniques used do not significantly alter the three morphological characters used in this study. Thus, changes could happen at a very slow rate and a much longer period of time in formaldehyde and ethanol of different concentrations and freezing is required before significant changes in body measurements can be detected (Figs. 1-14). The results are in agreement with the results of Billy (1982), Al-Hassan and Abdullah (1992), Al-Hassan and Al-Shawafi (1997), Al-Hassan et al., (2000), Jawad et al. (2001a,b), and Jawad (2003). The variation in the effect of different fixatives, preservatives and freezing condition could be explained on the basis that the different body regions of the fish body contain different chemical contents, thus behave differently when kept in different concentrations. The differences obtained might also be due to the genetic factors that rule the ratio of white to red muscles and the character of tissue water content (Leslie and Moore, 1986).

Live measurements could be calculated from the preserved fish by using the standard correlation factor (Sigler, 1949). This is a reliable practice as various authors have suggested (Parker, 1963; Stobo, 1972; Yeh and Hudson, 1975; Billy, 1982), it could be determined separately for each study, but not for the species in general (Yeh and Hudson, 1975). The determined correlation factor could be affected by several factors such as the original state of the fish; the time elapsed since preservation or fixation, and strength of the preservative or the fixative (Yeh and Hudson, 1975). Correlation factors are basically not reliable outside a specific study, as there is no standardization in fish fixation or preservation techniques. Rigor mortis might be the cause of the initial shrinkage when fish are killed and before they are placed in the fixative or preservative solutions. Thus, differences might appear between the different fixation and preservation techniques. In general, therefore, the standard correlation factor is not applicable, with the possible exception of using it to provide a preliminary rough study of specific approximations of the live state.

In conclusion, for S. longiceps, it could be stated that formaldehyde in different concentrations, as a fixative, causes no shrinkage or no effect criterion in the experimental cases. On the other hand, shrinkage is observed in the head length of fish kept in 10% formaldehyde mixed with distilled water only. No effect criterion has been observed in the total length of fish specimens fixed in formaldehyde 10% mixed with tap and distilled water and in the standard length of fishes fixed in formaldehyde 5% mixed with tap water. Except for the changes mentioned above, other fixative, preservative solutions and freezing technique showed incremental effects on the three body proportions used in this study.

 

Conclusions

The three body proportions of the two fish species, S. longiceps and S. leptolepis seemed to have been changed differently by the effects of the different concentrations of the fixative formaldehyde, the preservative, ethanol and the freezing technique. Increase in body proportions was the most common effect observed in the tests, although a number of shrinkage and no effect conditions were obtained as well.

 

Acknowledgements

Our sincere thank goes to the Ministry of Agriculture and Fisheries Wealth and the Directorate of Agriculture and Fisheries Development Fund for giving us the opportunity to work on the fish samples within the qualitative and quantitative distribution of marine organisms in the Sultanate of Oman and to provide the appropriate financial support.