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 7

 

Standard length, on the other hand, showed significant increase during the first 15-17 weeks of the experiment for the following methods of fixation and preservation - 10% formaldehyde solution with tap water and distilled water, 5% formaldehyde solution with distilled water and freezing.

Steady increase was noticed for the same period in the case of use of formaldehyde 5% mixed with tap water and ethanol 70% mixed with tap water. Standard length seems not to have been effected by the different solutions and freezing between weeks 15 and 18 until the end of the experiments. The common feature of the standard length in the case of preservation with ethanol 70% mixed with distilled water was not affected by this preservative and thus, gave longer periods of no effects.

Head length showed mainly dramatic and significant increase in all preservatives and fixatives solutions used in this study. On the other hand, fish specimens kept under freezing condition only one period of significant increase and that was in week 10 of the experiment. In the fixative formaldehyde 10% mixed with tap water, head length a shrinkage period for week 2-12. No effect period for these body measurements is observed in week 10 and upward.

S. leptolepis, except for the preservative ethanol 70% mixed with distilled water, the effect of the different fixatives, preservatives and freezing on the total length is characterised by slight variation involving steady increase all the way through the experiments (Figures 8-14). On the other hand, dramatic shrinkage followed by significant increase is observed in the preservative ethanol 70% mixed with distilled water.

Similarly and as in total length, the standard length of the fish specimens used in this study showed the same effect for six experiments out of seven. The fixative formaldehyde mixed with tap water was the only solution in which the standard length showed a significant shrinkage in the second week of the experiment.

For the head length, this body measurement showed variable effect when put in the different fixatives, preservatives and freezing conditions especially in the first 5 weeks. Periods of significant increase were observed in the fixative formaldehyde 5% mixed with distilled water and the preservative ethanol 70% mixed with tap water. Dramatic shrinkage was noticed when fish specimens kept in the fixative formaldehyde 10% mixed with distilled water and in the preservative ethanol 70% mixed with distilled water. No change effect or slight increase is observed when freezing technique is applied. In the middle of the experiments and during the weeks 5-12, dramatic increase in head length is observed for the formaldehyde 10% mixed with tap water, formaldehyde 5% mixed with tap water, ethanol 70% mixed with distilled water and in freezing technique. The head length showed no effect sign usually after the 13th week of the experiment.

For S. longiceps, the statistical analyses showed significant difference between degrees of increase in total length occurring in all fixative, preservatives solutions and freezing condition (P<0.005) except between formaldehyde 10% mixed with distilled water and formaldehyde 5% mixed with distilled water where the test showed no significant difference (P>0.005). Similar significant increase (P<0.005) in the degrees of increase is noticed in standard length. On the other hand, the statistical tests showed mainly no significant difference (P>0.005) in head length occurring in all fixatives, preservatives and freezing condition except between the two fixatives formaldehyde 10% mixed with distilled water and formaldehyde 5% mixed with tap water.

For S. leptolepis, the degrees of increase in total length showed no significant difference between the different fixative and preservative solutions (P>0.005) except the fixatives formaldehyde 10% mixed with tap water and formaldehyde 10% mixed with distilled water, and between the two preservative solutions. The freezing condition tests were all significant (P<0.005) except between the fixative solutions formaldehyde 5% mixed with tap and distilled water which were not significant (P>0.005). Significant difference in degrees of effects in standard length is observed between all the fixative, preservative solutions and freezing condition (P<0.005) except between formaldehyde 10% mixed with distilled water and formaldehyde 5% mixed with tap water, between the two preservative solutions, and between the freezing condition and other solutions where not significant (P>0005). The difference in degrees of effects between the results of the seven experiments were significant (P<0.005).

The effect of different fixatives, preservatives and freezing condition on the morphology of fish in relation to size has been the subject of several works (Burger, 1962; Stobo, 1972; Al-Hassan and Abdullah, 1992; Al-Hassan and Al-Shawafi, 1997; Al-Hassan et al., 2000; Jawad, 2003; Jawad et al., 2001a,b ). However, the results showed variable agreement and disagreement with their findings.