The First Occurrence of Xanthochromic Fish, Diplodus sargus (Family: Sparidae) in the Eastern Mediterranean

A single specimen white seabream, Diplodus sargus (Linnaeus, 1758), was recorded on 11 November 2019 from the coast of Konacık (Arsuz) in the Iskenderun Bay (North-eastern Mediterranean, Turkey). This specimen was identified as a specimen of Diplodus sargus. Known as Xanthochromism, abnormal skin coloration is an unusually yellow pigmentation in fishes. It is often associated with the lack of usual red pigmentation and its replacement with yellow. The present paper reported the first occurrence of the xanthochromic specimen of Diplodus sargus from Turkey's Mediterranean coast.

The white seabream (Diplodus sargus) distribution includes the Mediterranean Sea, southwestern Black Sea, and the Eastern Atlantic Ocean from the Canary Islands and Madeira north to Brittany and also off Angola (Froese & Pauly, 2020;Golani et al., 2006).
Diplodus sargus is widespread and commercially important species and also locally abundant in appropriate habitats throughout the Mediterranean.Diplodus sargus have been recognized two geographic subspecies in the European region: Diplodus sargus sargus is occur in the Mediterranean and Diplodus sargus cadeneti in the northeastern Atlantic from the Bay of Biscay to Senegal, including the Azores, Madeira, and the Canary Islands (Summerer et al., 2001).However, Domingues et al. (2007) stated that considering species' genetic in the D. sargus species group, no genetic differences were found between D. sargus and D. cadenati.Recently, Fricke et al. (2016) has defined and reported a new sea bream species as Diplodus levantinus n. sp.from the Israel coast (southeastern Mediterranean) Sea for the whole Mediterranean.
Xanthochromism is an unusually yellow pigmentation in animal.It is usually associated with a lack of normal red pigmentation and replacing it with yellow.Although xanthanthism in fish is known as a genetically based condition that causes abnormal skin color from yellow to orangegold, these species are rare in the seas.(Golani et al., 2019).Up to date, xanthochromic fish samples have been rarely reported in the Mediterranean.
In this study, the first xanthochromic case was reported for white seabream, Diplodus sargus from Iskenderun Bay, in the eastern Mediterranean Sea, Turkey, and up to date, no similar occurrence has been reported for this species in its native distribution area.

Materials and Method
One individual of Diplodus sargus was captured by spear gun from Konacık coast (Arsuz), Iskenderun Bay (36º20′N-35º48′E) at a depth of 12 m on 11 December 2019 (Figure 1).After capture, fresh specimen was placed on crushed ice and transported to the laboratory for more detailed examination.This specimen was identified as a xanthochromic specimen of Diplodus sargus (Figure 2).Morphometric measurements were carried out to the nearest 0.1 mm by a caliper and meristic counts.The specimen was deposited in the collection of the Laboratory Fisheries Genetic and Ecology, Faculty of Marine Sciences and Technology, Iskenderun Technical University, Iskenderun-Hatay.All counts and measurements follow Bauchot & Hureau (1986).

Results
The xanthochromic specimen of D. sargus had the following features: Body oval and deep, more or less compressed, back elevated.Scales on cheeks and opercle.Terminal mouth slightly protusible, lips thin.Jaws are reaching back to the vertical of anterior of eye.Eight incisiform teeth in front of upper and lower jaws, followed by well-developed 3-4 rows molar teeth (Upper Jaw: 28; Lower Jaw: 20).Gill rakers 15 (6+9) on the first-gill arch.Dorsal fin with 12 spines and 12 rays.Anal fin with three spines and 13 rays.Pectoral fin long and reaching well behind the anus with 15 rays.Pelvic fin origin behind pectoral fin origin with one spine and five rays.A small orange spot at the upper base of the pectoral fin.Lateral line scales 67 to caudal base.Body light yellow and orange with 18 longitudinal fine yellow lines.The detailed morphometric and meristic characters of the specimen are given in Table 1.
Colour: Head gold yellowish.Body with 8 light yellow vertical bands.Premaxilla area surrounding the eye and upper margin of operculum light yellow and orange.The membrane of spinous dorsal fin and dorsal ray light yellowish and orange.Pectoral and anal fins light to bright orange.The upper part of caudal peduncle light gold yellow.Caudal fin forked and hind edges dark orange.

Morphometric
Xanthochromism is characterized by a loss or severe reduction of darker pigments allowing the remaining non-melanin pigments to be unusually dominant (Pattengill-Semmens, 1999).As in some fish species, abnormal coloration is observed on the skin, where the average color is replaced by yellow.This situation is widely due to a lack of dark pigment, which has yellow forms green.In this case, all skin pigments except yellow and orange are lost in the fish.Quigley et al. (2017) declared these color anomalies in fish are seen as albinism, partial albinism, xanthochroism, melanism, and leucism.However, they stated these situations could be stem from skin pathologies, diet, hormonal imbalances, interspecific hybrids, and particularly, from nonlethal genetic mutations.
To date, there are several studies of xanthochromic fish species in the Mediterranean waters.These species are reported from coastal waters of Turkey (Akyol & Şen, 2012;Tokaç et al., 2013;Ulutürk et al., 2015), Nature Park Lastovo archipelago, eastern Adriatic Sea (Stagličić et al., 2019) and Israel (Golani et al., 2019).Golani et al. (2019) reported in this study, xanthochromic two demersal species: Epinephelus marginatus from the Israeli coasts of the Mediterranean Sea and D. vulgaris from the Lipsi, Dodecanese, Aegean Sea (Greece).Besides stated, a might probably be a xanthism specimen of Mediterranean horse mackerel, Trachurus mediterraneus in the same study, the first recorded specimen of Trachurus declivis from the Eastern Mediterranean Sea.
Recently, xanthochromic thinlip grey mullet, Chelon ramada has been reported from Izmir Bay in the Aegean Sea, Turkey by Akalın & Tosunoglu (2020).Also, the same authors stated that a xanthochroic individual of D. sargus was identified in Greece from a photo shared on the social media platform.
Although xanthochroic pigmentary anomaly has been reported for a number of fish taxa; it is still considered particularly rare.According to Carson (2011) this natural phenomenon often it is seen on a single specimen or with low population frequencies.
Here we report the first record on xanthochromic of white seabream Diplodus sargus in the eastern Mediterranean Sea.We hope that the study will contribute to the literature as the first color abnormality encountered in fish species in this region.

Figure 1 .
Figure 1.The location where (•) Diplodus sargus is caught in the Eastern Mediterranean, Turkey