Background

The razorbelly scad, Alepes kleinii (Bloch, 1793) is a reef associated, tropical marine fish species of the family Carangidae (Jack family).The dorsal surface of the Alepes kleinii is generally bluish grey to greenish grey, while ventral surface is lighter and more silvery in live specimens. In some specimens, dark vertical stripes are present above the lateral line and the presence of a large black spot on the upper operculum is also a key characteristic when identifying this species. The majority of the fins are transparent to pale in colour, with the caudal fin being predominantly yellowish. The razorbelly scad has predatory habits and generally preys upon small crustaceans, copepods, larval fish, lucifer shrimp, prawns, amphipods and fish eggs (Kalita & Jayabalan, 2000). It is widely dispersed throughout the Mediterranean Sea and Red Sea in the west (Adam, 1966), and most of the Indo-West Pacific region including the coast of Pakistan, south-eastern coast of India, Sri Lanka, Indonesia, Philippines, Taiwan, Papua New Guinea, Japan and northern Australia (Froese & Pauly, 2016). Although wide-ranging coast of Bangladesh is regarded as fisheries biodiversity hotspot (Chaklader et al., 2015; Hanif et al. 2015; Siddik et al. 2015; Chaklader et al. 2016; Siddik et al. 2016a; Siddik et al., 2017) but until this record, the razorbelly scad has previously been unreported in Bangladesh.

Therefore, this present study reports the occurrence of Alepes kleinii in the southwestern coastal waters of Bangladesh. This will represent the first record of a new species of the Carangidae family in this region, adding to the increasing list of carangid fishes inhabiting the fringes of coastal Bangladesh.

Methods

During a 3 month survey of the diversity of fish species in the coastal Baleswar River (22° 08′ 57” N, 89° 54′ 59″ E), Bishkhali River (21° 51′ 50” N, 90° 05′ 23″ E) and Burishwar River (21° 54′ 42” N, 90° 22′ 14″ E) from January to March, 2016 of southern Bangladesh, a total of 29 specimens of Alepes kleinii were collected by artisanal fishermen using gillnets. The fish were sourced from local markets within close vicinity of the aforementioned rivers. A typical sample of collected Alepes kleinii and its global distributed areas including Bangladesh are shown in Fig. 1 and Fig. 2, respectively. The captured specimens were preserved and transported to the laboratory for identification, morphometric measurements and meristic counts were conducted following standard methods. All morphometric measurements were recorded in centimeters (cm) taken with digital calipers and the weight of the fish samples were recorded to the nearest 0.01 g using digital electronic weighing balance (Shimadzu, EB-430DW, Japan).The length-weight relationship was calculated using the formula proposed by Ricker (1975) as:

$$ W={aL}^b $$
Fig. 1
figure 1

Razorbelly scad Alepes kleinii (Bloch, 1793) collected from the southern coast of Bangladesh

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Fig. 2
figure 2

Global distribution of Razorbelly scad, Alepes kleinii (Bloch, 1793) including newly report in Bangladesh

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Where, W is the weight of fish and L is the total length of specimen, a and b are the regression parameters of length weight relationship.

Results

A total of 29 specimens of Alepes kleinii were collected from fishermen’s catches for a period of three months from January to March, 2016 and identified as Alepes kleinii by a combination of characteristics using FishBase. Parameters used for identification included body colour (above and below lateral line), dark vertical strip, colour of caudal fin, black spot on operculum, number of dorsal fin, ventral spine, shape of caudal lobe, number of fin rays, strongly arched lateral line. The total length of collected specimens ranged from 8.6 to 15.8 cm and body weights varied between 9.61 to 51.47 g. All morphometric measurements and meristic counts recorded from the specimens are presented in Table 1. The results of length weight relationship are presented in Fig. 3.

Table 1 Morphometric measurements and meristic counts of razorbelly scad, Alepes kleinii (Bloch, 1793) collected from the southern coast of Bangladesh (n = 29)
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Fig. 3
figure 3

Length-weight relationships of razorbelly scad, Alepes kleinii (Bloch, 1793) collected from southern coast, Bangladesh

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Systematics

Order: Perciformes (Bleeker, 1859).

Family: Carangidae (Rafinesque, 1815).

Genus: Alepes (Swainson, 1839).

Alepes kleinii (Bloch, 1793).

Common name: Razorbelly scad (English), Macarela bandoneada (Spanish).

Discussion

The minimum and maximum fork length (FL) of 29 recorded individuals was 7.5 cm and 13.5 cm respectively, although Alepes kleinii can grow to a maximum 16 cm in length (FL) (Smith-Vaniz, 1984).The regression parameter b of length weight relationship for Alepes kleinii (b = 2.81), was found to be within the expected normal range of 2.5 < b < 3.5, as compared with the Bayesian LWRs predictions approach in FishBase (Froese, 2006; Siddik et al. 2016b; Islam et al. 2017; Hanif et al. 2017a). This indicates that this species will grow more in weight than in length and the coastal waters of Bangladesh are conducive for supporting the growth and development of this species.

Species distribution is influenced by a large number of environmental factors such as the geological history of the area, environmental stability, ecosystem productivity, habitat heterogeneity and suitability, and competition and predation (Legalle et al. 2008; Alshawy et al. 2016). Several vectors including patterns of water circulation, currents, and sea warming may provide suitable conditions for the expansion of its distribution range (Gurlek et al. 2016). Although, it is not exact whether the Alepes kleinii is endemic to the coastal Bangladesh region, or a recent migrant into these waters, despite the nearest reported findings being Sri Lanka (Robins et al. 1991) and South-East India (Kapoor et al. 2002). The authors agree with the proposition of Mahapatro et al. (2017), that fish always seek better environmental conditions can lead to alterations in geographical distribution. Furthermore, frequent climatic changes and human interventions have worked altogether to distribute species in new areas far from their natural habitat (Hanif et al. 2017b). Since the species have extended distribution throughout the Indo-West Pacific region, there is a possibility of climate changes led to a rise in the sea surface areas could have caused the fish dispersed from their native range to the coast of Bangladesh.

Conclusion

According to the information collected through independent web-based search, the occurrence of razorbelly scad, Alepes kleinii is novel in the coastal region of Bangladesh. As the Alepes kleinii is within the same family as 37 other carangid species inhabiting southern Bangladesh, this particular fish has the potential to increase its range and adapt to the unique fisheries hotspot of southern coastal Bangladesh.