Lobe Of Caudal Fin Research Articles

Differential cropping of the caudal fin lobes of prey fishes by the piranha, Serrasalmus spilopleura Kner

Regression analysis of log10 upper and lower caudal lobe area (whole ‘uncropped’ caudals) against log10 standard length for ten prey species of the piranha showed significant differences in both slope and intercept for only one species (Astyanax fasciatus) although intercepts alone were significantly different for two others (A. bimaculatus and Poecilia vivipara). Caudal lobe — standard length regression statistics were used to generate estimates of caudal lobe loss in cropped prey species and these clearly demonstrated highly significant differential cropping incidences in several species and size categories. Particularly in the Astyanax species, the upper caudal lobe was subject to low cropping loss and the lower caudal lobe to high cropping loss. Differential cropping of caudal fin lobes suggests that piranha initiate their attack from below and behind prey fishes.

A natural hybrid between two tropical fishes: Semaprochilodus insignis x Semaprochilodus taeniurus (Teleostei, Characoidei, Prochilodontidae)

lnterespecific hybridization has become a rather widespread phenomenon among fish groups (Hubbs, 1955). The incidence of natural hybridization among freshwater fishes seems to be a function of environment, decreasing gradually from north temperate to tropical zones. It also appears to be in­ versely correlated with diversity and therefore, in the tropical highly diverse fish fauna of the Amazon region, only a low frequency of natural hybrids may be expected. However, it is probable that in this region some hybrids have already been studied and identified as distinct species while others are still to be discovered. This paper concerns ecological and morphological aspects of three Amazonian forms of the genus Semaprochilodus Fowler (Characoid, Prochilodontidae) and provides evidences on this respect. Semaprochi/odus insignis (jaraqui escama grossa) and S. taeniurus (jara­ qui escama fina) are two median size, sympatric species of high abundance in Central Amazonia. During their extensive and complex migrations (Ribeiro, 1983) a third cryptic species (jaraqui-acu) was found in a very low frequency (1 :880 individuaIs) mixed to individuaIs of both species but never in isolated schoo!s. ln the beginning of the annual floods schools of mature males and females of both species of jaraquis were captured in Rio Negro migrating downstream to spawn in the turbid waters of Rio Amazon. Mature males of jaraqui-acu were also found in these schools. Females of jaraqui-acu were never captured in the spawning area nor were they found in state of sexual maturation throughout the year. ln this pape r 54 individuaIs of S. insignis, 48 of S. taeniurus and 42 of jaraqui-acu were used for the morphological study of these three forms. All individuaIs were collected with non-selective beach seines from schools mi­ grating in Rio Negro. All measurements and counts were based in the last review of the genus Semaprochilodus (Mago Leccia, 1972). The amplitudes of variation and means of body proportions and counts are presented and they were analized by the method of overlap of means (Royce, 1957). The diffe­ rences between two means were tested in terms of common standard deviation of samples and the value of three standard deviations was taken as indicative of interspecific differences between two samples. This value corresponded to 13% of overlap between the samples and the percentage of characters distinct at this leveI constituted the interspecific differenciation degree. The following comparisons can be obtained from Table 1: The jaraqui-acu is neither so elongated as S. taeniurus nor so deep as S. insignis. ln this new form, its back is but little more elevated than in this first species but not sharply so as in the former. Post dorsal region not so straight so that upper profile is sinous and forms an obtuse angle at origin of dorsal which is intermediate as compared to both species. Lower profile more or .Iess evenly convexo Therefore, body shape is neither smooth and linear as in S. taeniurus nor rhomboid as in S. insignis. Dorsal, anal, pectoral and pelvic fins are inserted in an intermediate position in jaraqui-acu as com­ pared to S. insignis (behind) and S. taeniurus (in front). Body coloration is similar to that of S. insignis especially in the reddish pectoral and pelvic fins. The number of black bands in each lobe of caudal fin in jaraqui-acu (3-6) is intermediate between that of S. taeniurus (3-5) and S. insignis (3-7). All

Effects of Median-Fin Amputation on Fast-Start Performance of Rainbow Trout (Salmo Gairdneri)

ABSTRACT Fast-start performance of eight groups of rainbow trout with various fin-rays removed was measured to test the hydromechanical theory (Weihs, 1973) that large fins are required for acceleration. A trend towards decreasing performance was found for the following sequence of fin-ray amputations: control (pelvic rays amputated); dorsal fin; anal fin; dorsal lobe of caudal fin and ventral lobe of caudal fin; ventral lobe of caudal fin and anal fin; dorsal and ventral lobes of caudal fin; both caudal-fin lobes and anal fin. The series represents progressive reduction in fin and body area, as well as reduction in these areas where lateral movements are largest. Effects of fin amputation on performance were statistically significant (P > 0·05) in comparison with controls only for the last three groups lacking the caudal fin. The results confirm the hydromechanical theory, and lead to the conclusion that mechanically optimum lateral body profiles for faststart and for steady (cruising and sprint) performance are mutually exclusive. This mechanical restriction can be circumvented only in bony fish, with the evolution of flexible, collapsible fins that permit major variation in lateral body profile.

Effects of Partial Caudal-Fin Amputation on the Kinematics and Metabolic Rate of Underyearling Sockeye Salmon (Oncorhynchus Nerka) At Steady Swimming Speeds

ABSTRACT Propulsive wavelength, tail-beat frequency, trailing-edge amplitude, critical swimming speed and oxygen consumption rates have been measured for sockeye salmon in which the trailing edge depth and caudal-fin area were variously reduced by partial caudal-fin amputation. The swimming mode was sub-carangiform. The 45 min critical swimming speed for intact fish was 61·6 cm/sec (3·0 l/sec). The critical speed was not significantly reduced by removal of either the epaxial or hypaxial caudal-fin lobes, but was reduced significantly (P < 0·05) to 51·8 cm/sec (2·5 l/sec) when both lobes were removed. The mean length of the propulsive wave was 1·00 body length, and was not affected by the caudal-fin surgery. Both tail-beat frequency and amplitude increased with speed, their product linearly so. Normalization of data in relation to the physiological maximum at the critical swimming speed showed no relative changes in frequency and amplitude. No significant differences were observed in standard or active metabolic rates. General equations describing thrust (Lighthill, 1969) and drag were compared. It was shown that the drag on the caudal fin was markedly increased by lateral propulsive movements as suggested by Bone ‘s boundary-layer thinning hypothesis (Lighthill, 1971). Drag coefficients for the caudal fin were one to two orders of magnitude higher than would be expected in the absence of lateral movements. It is considered that the principal function of the caudal fin is in manoeuvre and acceleration.

South American Cyprinodont Fishes Allied to Cynolebias with the Description of a New Species of Austrofundulus from Venezuela

Austrofundulus dolichopterus is described as a new species of annual cyprinodont and was recently discovered in temporary ponds in the states of Guarico, Cojedes, and Apure, Venezuela. It is placed in Austrofundulus on the basis of caudal fin shape and color pattern. It differs from other species of this genus by lacking caudal fin scales, in having elongate streamers on the caudal fin, elongate dorsal and anal fins, and a dorsal fin slightly in advance of the anal fin. In an attempt to determine its closest relatives, characters defining the South American cyprinodont genus Cynolebias and its allies were reevaluated. It was found that Cynolebias, Pterolebias, Cynopoecilus, Rachovia, Austrofundulus, Leptolebias, and Simpsonichthys cannot be separated on the basis of characters currently in use such as the relative positions of the dorsal and anal fins, caudal peduncle and fin shape, distribution of scales on the caudal fin, sexual dimorphism in the number of dorsal and anal fin rays, and variations in the presence or the juxtaposition of the two pelvic fins. Despite these findings, we do not believe it wise to synonymize any of these genera until reevaluation of all neotropical cyprinodont genera can be accomplished. When sufficient material becomes available for a more complete study, some of the genera here tentatively recognized may prove to be valid on the basis of other characters. For example, northern South American annual fishes tend to have pointed upper and lower caudal fin lobes and have scales distributed over the caudal fin. Southern species have a rounded or simple pointed caudal fin and lack scales on the caudal fin. Further study may show these differences to be of generic significance.