Pug-Headedness Anomaly in a Wild and Isolated Population of Native Mediterranean Trout Salmo trutta L., 1758 Complex (Osteichthyes: Salmonidae)

Abstract

Skeletal anomalies are commonplace among farmed fish. The pug-headedness anomaly is an osteological condition that results in the deformation of the maxilla, pre-maxilla, and infraorbital bones. Here, we report the first record of pug-headedness in an isolated population of the critically endangered native Mediterranean trout Salmo trutta L., 1758 complex from Sardinia, Italy. Fin clips were collected for the molecular analyses (D-loop, LDH-C1* locus. and 11 microsatellites). A jaw index (JI) was used to classify jaw deformities. Ratios between the values of morphometric measurements of the head and body length were calculated and plotted against values of body length to identify the ratios that best discriminated between malformed and normal trout. Haplotypes belonging to the AD lineage and the genotype LDH-C1*100/100 were observed in all samples, suggesting high genetic integrity of the population. The analysis of 11 microsatellites revealed that observed heterozygosity was similar to the expected one, suggesting the absence of inbreeding or outbreeding depression. The frequency of occurrence of pug-headedness was 12.5% (two out of 16). One specimen had a strongly blunted forehead and an abnormally short upper jaw, while another had a slightly anomaly asymmetrical jaw. Although sample size was limited, variation in environmental factors during larval development seemed to be the most likely factors to trigger the deformities.

Pugheadedness in Fishes

“…Exophthalmia (protrusion of the eyeballs from the skull, or 'pop eye') can be associated with the deformity (e.g. Sutton 1913;Gudger 1930;1937;Mansueti 1960;Isaacson 1965;Chew 1973;Shariff et al 1986;Palmas et al 2020), but is not always markedly obvious or present (e.g. Gudger 1930;Goodwin and Vaughn 1968;Bortone 1971Bortone , 1972Franks 1975;Pickett 1979).…”

“…In rainbow trout Oncorhynchus mykiss there is evidence for vertebral deformities being partially caused by inbreeding (Aulstad and Kittelsen 1971); however, inbreeding was excluded as a factor causing vertebral deformity in Atlantic cod Gadus morhua (Gjerde et al 2005). Inbreeding was also rejected in a study of pugheaded Mediterranean trout Salmo cettii from a Sardinian stream, based on expected heterozygosity estimates (Palmas et al 2020). Hybridization can occasionally cause relatively high incidence of pugheadedness, along with other skull and jaw deformities, as seen in white bass Morone chrysops × striped bass M. saxatilis hybrids and their backcrosses in Hickey et al (1977).…”

First record of pugheadedness in Crenicichla cf. missioneira Lucena & Kullander, 1992 (Cichliformes: Cichlidae)

“…Conversely, Hickey (1972) observed that some specimens had the same efficiency in capturing prey, due to an enhancement in the binocular vision caused by the lifting of the eyes. In salmonids, despite the deformity, the authors found no relevant differences between normal and deformed trout, suggesting that the deformed specimen was robust and healthy (Palmas et al, 2020). Gudger and Miller (1929) mentioned two opposing scenarios: a pugheaded trout that struggled to capture the bait due to a lack of premaxilla, but a capture of an adult with a significant weight, revealing that the lack of food acquisition was not a factor to consider.…”

Changes in Dendritic Spine Morphology and Density of Granule Cells in the Olfactory Bulb of Anguilla anguilla (L., 1758): A Possible Way to Understand Orientation and Migratory Behavior

“…Eels were collected between November 2019 and January 2021 from the Pramaera River (Central-Eastern Sardinia, Italy). The Pramaera River is a typical Mediterranean small watercourse characterised by biseasonal climatic features, with hot arid summers, rainy autumn/winter seasons along with extreme precipitation events, determined irregular flow, and strong seasonal hydrological fluctuations [ 72 , 73 , 74 , 75 ]. The river showed well-oxygenated waters (dissolved oxygen = 9.40 ± 12.35 mg L −1 ), good conductivity (1324.16 ± 1564.71 µS cm −1 ), and typically Mediterranean average water temperatures (16.01 ± 5.32 °C).…”