Do body and fin form affect the abilities of fish to stabilize swimming during maneuvers through vertical and horizontal tubes?

Goldfish, Carassius auratus, silver dollar, Metynnis hypsauchen, and angelf ish, Pterophyllum scalare were induced to swim through narrow vertical and horizontal tubes ranging in length from 0 to 20 cm (approximately 0 to 3 ti mes total fish length, FL). The ability to stabilize the body while negotia ting these confined spaces was quantified as (1) the minimum width of verti cal (w(v)) and horizontal (w(h)) tubes traversed, where width is the smalle r cross-sectional dimension of the tube, (2) the ratio w(v)/w(h), and (3) t ransit speed through the tubes. Tube width was expressed as relative width, obtained by dividing tube width by fish length. Minimum relative widths tr aversed increased from 0.15 to 0.19 in the order silver dollar < angelfish < goldfish for vertical tubes and from 0.17 to 0.18 in the order goldfish = silver dollar < angelfish for horizontal tubes. w(v)/w(h) increased from 0 .91 to 1.10 in the order silver dollar = angelfish < goldfish. Minimum tube widths generally increased with tube length for vertical tubes. Although s ignificant differences in relative minimum widths among species were found, these were small. In contrast, for horizontal tubes, there was no signific ant effect of tube length on minimum tube width for any species. Large diff erences were found in transit speed. Transit speed generally decreased as t he tube length increased. The slope of the relationship between transit spe ed and tube length varied among species generally increasing from - 0.41 to - 1.16 for horizontal tubes in the order goldfish < silver dollar < angelf ish and from - 0.42 to - 1.07 in the order silver dollar < goldfish < angel fish for vertical tubes. As a result, goldfish usually took longest to trav erse tubes of zero length but the shortest time to traverse the longest tub es. In contrast, angelfish traversed short tubes in the least time and long tubes in the greatest time. Deeper bodied angelfish swam slowly and traver sed tubes with difficulty because they required experience during each tria l to replace median and paired fin with body and caudal fin swimming. Accor ding to our data, goldfish were best able to swim in confined spaces.