LOW-COST COMPUTER-ASSISTED IMAGE-ANALYSIS FOR FISHERIES RESEARCH

An image analysis system based on the Macintosh personal computer and public domain software (NIH image, version 1.57) allows capture of dig itized images for data analysis. Three techniques for image capture an d aquisition of linear and area measurements from digitized images wer e tested: (1) estimation of egg size, (2) estimation of number of eggs or fry, and (3) measurement of fish length. For estimation of egg siz e, egg samples were taken by catheterization from two female channel c atfish Ictalurus punctatus. Egg diameters measured manually (1.82 +/- 0.27 and 2.59 +/- 0.19 mm) were not significantly different (P = 0.08 and 0.20) from the diameters estimated with image analysis (1.92 +/- 0 .21 and 2.63 +/- 0.17 mm). For egg counting, channel catfish eggs were hand-stripped into Hanks' balanced salt solution and divided into sev en 15-mL aliquots. The number of eggs was determined manually and imag es were captured for analysis. The number of eggs determined manually (436 +/- 41) was not significantly different (P = 0.80) from the numbe r estimated with image analysis (430 +/- 43). Also, total lengths were measured manually on 50 fingerling channel catfish and 50 fingerlings of the hybrid channel catfish x black bullhead Ameiurus melas. An ima ge of each fish was also recorded for measurement by image analysis. R eplicate sets of measurements were made by three individuals with diff erent levels of experience with the computer system. The mean (+/-SD) of total lengths measured manually for the channel catfish fingerlings (242 +/- 33 mm) was not significantly different (P = 0.37) from the l engths determined by image analysis (237 +/- 33, 235 +/- 33, and 231 /- 34 mm). The mean of total lengths measured manually for the hybrids (157 +/- 39 mm) was not significantly different (P = 0.98) from the l engths measured by image analysis (158 +/- 40, 157 +/- 39, and 155 +/- 39 mm). The availability of public domain software and inexpensive or commonly available input devices make image analysis more accessible to researchers.