First record of morphological abnormality in embryos of Urotrygon rogersi (Jordan & Starks, 1895) (Myliobatiformes: Urotrygonidae) in the tropical Eastern Pacific/Primer registro de Anomalia morfologica en embriones de Urotrygon Rogersi (Jordan & Starks, 1895) (Myliobatiformes: Urotrygonidae) en el Pacifico Oriental tropical.
Reported morphological abnormalities for elasmobranchs correspond to occurrences of bicephalia (Castro-Aguirre & Torres-Villegas, 1979; Goto et al., 1981; Bornatowski & Abilhoa, 2009), albinism (Joseph, 1961; Talent, 1973; De Jesus-Roldan, 1990; Ben-Brahim et al., 1998; Clark, 2002; Ferreira & Goes, 2002; Rider et al., 2002; Saidi et al., 2006; Sandoval-Castillo et al., 2006; Bottaro et al., 2005, 2008), anophthalmy (Gomes et al., 1991; Ribeiro-Prado et al., 2008) and deformities in the axial skeleton (Springer, 1960; Bensam, 1965; Du Built, 1978; Mancini et al., 2006). However, the most common abnormalities in skates (Order Rajiformes) and rays (Order Myliobatiformes) is where the pectoral fins are not fused to the head. This type of abnormality had been recorded by different authors (i.e. Templeman, 1965; Honma & Sugihara, 1971; Lamilla et al., 1995; Rosa et al., 1996; Oldfield, 2005; Ribeiro-Prado et al., 2008; Escobar-Sanchez et al., 2009) for several species of the family Rajidae (i.e. Raja brachyura, R. asterias, R. clavata, R. radula, R. radiata, R. miraletus, Amblyraja radiate, Atlantoraja castelnaui, A. cyclophor, A. platana), Torpedinidae (Torpedo marmorata), Rhinobatidae (Rhynchobatus djiddensis), Gymnuridae (Gymnura poecilura), Potamotrygonidae (Potamotrygon motoro), Dasyatidae (Dasyatis longa, D. dipterura, D. akajei, Himantura uarnak, Pteroplatytrygon violacea) and this paper reported it for first time to family Urotrygonidae, specifically to Urotrygon rogersi in the Tropical Eastern Pacific, its known distribution area.
The pregnant females were caught by artisanal fishermen who use trawl gill net (2.75 inch mesh size) to catch shrimp. One of them was captured in December 2007 in El Tigre (3[degrees]52'N, 77[degrees]19'W), the and another one in April 2008 in El Bajo de Punta Soldado (3[degrees]47'N, 77[degrees]11'W), central Pacific coast of Colombia. The females were dissected and their embryos were photographed and preserved in 10% formalin. The species identification was based on characters described by McEachran & Di Sciara (1995) and Robertson & Allen (2008). These U. rogersi were distinguished from other species of the genus, for showing small denticles on snout along the margin of disc, the area behind scapular region at midline of disc; a row of thorns from nape along middle of the back and top of the tail to base of spine; denticles arranged in longitudinal rows on top of body cavity; a plain light brown to brown coloration without distinctive marks in the top and white below. Morphometric measurements of the females and embryos were taken to the nearest 0.1 mm according to McEachran & Di Sciara (1995).
A pregnant female was 29.0 cm total length (TL), 15.5 cm disc width (DW) and 151 g, with two male embryos in the left uterus. One of the males was well developed (12 cm TL, 7.5 cm DW, 8 g) (Fig. 1a), but the smaller one (9.5 cm TL, 6.0 cm DW, 5 g) presented abnormality in the disc. The left pectoral fin was neither well-formed nor fused in front of its head, its snout was not completely free, and only its right pectoral fin was projected forward on side; also the pelvic fins were rounded and not located at the same level; and the spiracles were very open (Fig.1b). In addition, its dorsum presented a fin-like projection or "dorsal fold" in the middle zone (Fig. 1c), and its mouth and nostrils were well developed.
The smaller pregnant female (23.2 cm TL, 12.5 cm DW and 65.44 g) had one abnormal developing male embryo of 6.2 cm TL, 3.7 cm DW and 0.9 g in the left uterus. This embryo also presented a left pectoral fin not fused in front of its head, its snout was not completely free, and only its right pectoral fin was projected forward on side (Fig. 2a). The nostrils and mouth were well developed, although the last one was slightly to one side, but apparently functional (Fig. 2b).
How was cited above, the morphological abnormalities more frequent in rays correspond to the pectoral fins non-adherent to the head which is produced in the early development and is known as "Batman" ray; in this abnormality, the rays present its snout free and its pectoral fins projected forward on each side. In the two found abnormal embryos, only the left pectoral fin was not fused to the head, its snout was not completely free, and only its right pectoral fin was projected forward on side. Those characteristics could be indicating an interruption on the early development; however, the fin-like projection on the disc in one of them could correspond to a malformation, which not presented its bigger and well-developed sib.
The causal factors of malformations could be parasitic infection, arthritis, injury, tumors, bad nutrition, congenital abnormality (Heupel et al., 1999), or unfavorable environmental conditions during embryonic development, such as pollution (Haaker, 1977; Rodriguez-Romero et al., 1990; Grady, 1992). Although in the case of U. rogersi, the cause of morphological deformities is uncertain, could be suggested, initially, that a bad nutrition and/or a congenital abnormality could be the causes of this malformation. The first reason can be considered by the presence of another well developed embryo (sib), which could have taken more feed from its mother, securing its development and better growing, supported that by the bigger length and weight. However, the second reason is supported by the presence of a fin-like projection or "dorsal fold" that is not present in these species, so corresponding to a congenital abnormality; this malformation had been recorded to Gymnura micrura in Brazilian waters (Silva-Nunes & Magalhaes-Piorski, 2009). On the same way, the other unique embryo appeared to have a faster embryonic grow than the average of that population, since with only 6.1 cm TL, it presented a light brown dorsum, while others embryos of similar size have a light pink dorsum (pers. obs.) indicating an earlier development state. However, this faster growth was not an advantage to this animal, since it was not a well-developed embryo. Taking this into consideration, it is suggested that the cause of the morphological deformities during embryonic development in these individuals could be a congenital abnormality and not caused by bad or poor nutrition.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
The unfavorable environmental conditions are discard, not only because the other embryo was well developed, but also because the areas where the pregnant females were captured are conserved zones, without contamination, industrial discharges, and at present one of them is in process of be declared natural reserve (INVEMAR et al., 2006).
Rosa et al. (1996) propose that this type of abnormality does not affect the survival of individuals of Potamotrygon motoro based on the capture of juveniles and adults alive with this malformation; while Escobar-Sanchez et al. (2009) suggest that specimens of Dasyatis longa may die before reaching the adulthood. Based on the degree of deformity in the disc of the analyzed embryos and since the mobility of U. rogersi is specially based on the undulation of pectoral fins (rather than the tail) (Wilga & Lauder, 2004), it is possible that these individuals had difficulties in swimming and escaping from potential predators (sharks), and secondly, its capabilities as a predator would be significantly limited, even with their well-formed mouths that will allow them to feed on their prey such as polychaetes, shrimps and crabs (Navia et al., 2009).
Finally, one record of similar abnormality was presented in a male embryo of Pteroplatrygon violacea captured in southeastern Brazil, which presented an incomplete fusion of the left pectoral fin and the body and also an asymmetry regarding the pectoral fins (Ribeiro-Prado et al., 2008); the authors proposed than the percentage of this abnormality is low for this specie (1.3%), even being the highest from other species of the same area. Although that authors proposed that the percentage of abnormalities estimated in several studies are not representative of the real number, because in all cases samples came from fisheries, where the capture total are uncertain, in this study, the samples were collected from monthly scientific surveys during three years, obtaining a low percentage of this abnormality to U. rogersi (0.31%), suggesting that in the study area this embryonic abnormality is not frequent. However, it is suggested to evaluate the presence of abnormalities in other sympatric species of the genera Dasyatis, Gymnura, Narcine and Rhinobatos, comparing them with abnormalities recorded in other areas of the world, and including radiographies and dissections to try to assess the causes of that abnormalities.
We thank Hernan Paredes and Florentino Cuero, fishermen of the localities of Juanchaco and La Bocana, respectively, who captured and donated us the female specimens; C. Mejia for the revision of the English. The samples were collected during the field phase of the research project "Biodiversity and life history of rays of the Pacific Coast of the Valle of Cauca, Colombia" developed for the SQUALUS Foundation, which is co-financed for PADI Foundation and the Initiative to threaded species (IEA).
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Received: 10 February 2010; Accepted: 26 December 2010
Paola A. Mejia-Falla (1), Andres F. Navia (1) & Luis A. Munoz (1)
(1) Colombian Foundation for Research and Conservation of Sharks, Skates and Rays SQUALUS Carrera 79 No. 6-37 Cali, Valle del Cauca, Colombia
Corresponding author: Paola A. Mejia-Falla (email@example.com)
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|Title Annotation:||Short Communication|
|Author:||Mejia-Falla, Paola A.; Navia, Andres F.; Munoz, Luis A.|
|Publication:||Latin American Journal of Aquatic Research|
|Date:||Mar 1, 2011|
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