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

 Dawood S. Al-Mamry1, Laith A. Jawad1,2 and Juma M. Al-Mamry1


1 Marine Science and Fisheries Centre, Ministry of Fisheries Wealth, P. O. Box 427, Postal Code 100, Muscat, Sultanate of Oman

2 Corresponding author: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Abstract

The fixative, formaldehyde, the preservative, ethanol and the freezing technique were chosen to show their effect on three morphological characters of two fish species, Sardinella longiceps (Family: Clupeidae) and Selaroides leptolepis (Family: Carangidae) collected from Oman Sea, Sultanate of Oman. The results showed a variable effect of fixatives, preservatives and 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

Keywords: fixation, preservation, freezing, morphology, clupeidae, Muscat, Oman

 

 

 

Introduction

Various methods including fixation, preservation and freezing technique are used to preserve fish specimens so that they are available for further studies, e.g. biosystematics work. Formaldehyde, ethanol and freezing are the standard ichthyological material and method in this aspect.

Body proportions of preserved fish showed variable degrees of change after a standard period of fixation, preservation and freezing. Most authors have reported a decrease in length (Lux, 1960; Parker, 1963; Stobo, 1972; Engel, 1974; Sayers, 1987), but Billy (1982), Al-Hassan and Abdullah (1992), Al-Hassan and Al-Shawafi (1997), Al-Hassan et al. (1999, 2000) and Jawad (2003) reported either slight or significant increase in the body proportions of the fish species they have studied.

So far, no report has been published on the effect of fixatives, preservatives and freezing on body proportion of fishes of Oman. Thus, a practical evaluation of the effect of formaldehyde, ethanol and freezing on certain body measurements in two fish species obtained from Omani waters was carried out.

The aim of the work at hand is primarily to document the artificial morphological changes which may hamper identification and accurate taxonomic description.



Twenty one specimens of each of the species S. longiceps and S. leptolepis were obtained from the Gulf of Oman (Sea of Oman or Arabian Sea) at the City of Muscat, Sultanate of Oman. Fish of similar size and age were chosen to obviate size and age effects (standard length (SL) range 109-116 and 116-129 mm for S. longiceps and S. leptolepis respectively, estimated to be two years old). Measurements were taken within an hour of capture. Specimens were divided in seven lots of 3 fish to be used for formaldehyde, ethanol and freezing experiments. Fixative solutions were prepared as follows: two lots of 5% formaldehyde, two lots of 10% formaldehyde. Preservative solutions were prepared as follows: two lots of 70% ethanol. Each pair of the fixatives and preservatives being mixed with tap and distilled water. The seventh lot was used for the freezing experiment, for which a one cubic metre commercial deep freeze unit was used. Body dimensions chosen were total length (TL), standard length (SL) and head length (HL) (widely used by taxonomists and fisheries biologists), giving a total of 21 experimental variables. Each specimen was measured weekly over a twenty-week period. Duncan's multiple test was applied to examine the effect of different fixatives, preservatives and freezing on body proportions (Harraway, 1997).