Iranian Journal of Fisheries Sciences 19(2) 814-832 2020 DOI: 10.22092/ijfs.2018.120044. Use of otolithic morphometrics and ultrastructure for comparing between three goatfish species (family: Mullidae) from the northern Red Sea, Hurghada, Egypt Osman A.G.M.1*; Farrag M.M.1; Mehanna S.F.2; Osman Y.A.3 Received: December 2017 Accepted: July 2018 Abstract This work highlights the role of otolithic morphometrics, shape indices and ultrastructure in the identification of three Mullidae species from the Red Sea. Differences in otolithic measurements were detectable in all three-goatfish species. The statistical analysis of otolithic morphometric parameters showed that otolithic measurements are good indicators of fish size. For all three species, the correlation between fish length and different otolithic variables was statistically significant. The coefficient of determination (r2) ranged from 0.83 to 0.92 in the three species, being higher for M. vanicolensis in all cases. The otolith area of M. vanicolensis was most strongly related to fish length, with a high correlation between otolith area and fish length (r2=0.92) being observed in this species. The mean values of the six examined shape indices of the otoliths were considerably different among the three species, and the high degree of differentiation of these indices among species makes them useful for other researchers who wish to use otoliths in fish identification and classification. Remarkable variations in the morphological characteristics of fish otoliths were recorded among the studied species via scanning electron microscopy, including variations in the ornamentation of the ostium, cauda, and column of the otolith. These differences in otolithic characteristics and morphology might be useful for fisheries, biologists, archaeologists and geologists in discriminating Mulloidichthys flavolineatus, M. vanicolensis, and Parupeneus forsskali. This work contributes to the bioecological knowledge regarding commercially important fishes and provides key information for studying the trophic ecology of fish-eating species and fishery management. Keywords: Goatfish species, Otoliths, Morphometrics, Scanning electron microscope, Red Sea 1-Department of Zoology, Faculty of Science, Al-Azhar University (Assiut Branch), 71524 Assiut, Egypt. 2-National Institute of Oceanography and Fisheries, Suez, Egypt 3-National Institute of Oceanography and Fisheries, Hurghada, Egypt *Corresponding author's Email: [email protected] 815 Osman et al., Use of otolithic morphometrics and ultrastructure for… Introduction taxonomical and biological archives, as Family Mullidae (Goatfishes) is widely they reflect species’ growth and distributed globally, especially in the development. Most importantly for the Pacific and Indo-Pacific regions, current study, otolithic morphology is representing important food-chain species specific (Popper et al., 2005). components in coastal ecosystems Otolithic morphology ranges from (Pavlov et al., 2015). The family ellipsoidal to more complex shapes, consists of six genera and with protrusions and invaginations approximately 62 species (Nelson, (Campana, 2004), and has been used in 2006). Goatfishes are one of the most many studies for species identification economically and commercially (Tuset et al., 2006; Lord et al., 2012; important groups inhabiting the Bani et al., 2013; Sadighzadeh et al., northern Egyptian Red Sea sector 2014). However, for accurate species (Sabrah, 2015). Three common goatfish identification, a reference collection of genera are present along the Egyptian otoliths from known species must be Red Sea coast: Mulloidichthys, produced to generate sufficient Parupeneus and Upeneus (Kuronuma comparative material to produce and Abe, 1986). accurate descriptions of morphological Otoliths are calcareous structures characteristics. found in the inner ear of fishes To our knowledge, there is no (Campana, 2004). There are three pairs available information concerning the of otoliths (sagittae, asterisci and lapilli) identification of goatfish from the in the otic sacs (Popper and Lu, 2000), Egyptian Red Sea using otolithic and they function as mechanoreceptors morphometrics and∕or ultrastructure. that are involved in balance and hearing Therefore, this study had three (Popper et al., 2005). In most species, objectives: 1) to determine the the sagittal otoliths (the largest of the possibility of readily discriminating three otolith pairs) are most commonly common goatfish species based on the used to estimate age and growth, shape and ultrastructure of their movement and habitat, population otoliths; 2) to quantify otolith length, structure, and trophic ecology width, and height relationships with (Campana and Casselman, 1993; respect to fish length; and 3) to identify Rooker et al., 2008). Otoliths are often characteristics and ultrastructural collected in routine fisheries features allowing otoliths from common investigations for age determination as Mullidae species to be distinguished well as from predator stomachs from each other. (Nielsen and Andersen, 2001), allowing precise information on the Materials and methods length, weight, age, and quantity of Sampling individual fish prey to be obtained in Three goatfish species (Family: many cases. Furthermore, otoliths are Mullidae) were collected (n=275) from generally considered to serve as the northern part of the Red Sea Iranian Journal of Fisheries Sciences 19(2) 2020 816 Province at Hurghada (latitudes 27° 10' total length (TL) was measured to the N–27° 33' N and longitudes 33° 70' E– nearest millimeter and weight (W) to 33° 85' E) (Fig. 1) using artisanal the nearest gram. The sagittal otoliths fishing gear (gill net and trammel net) (Fig. 2) of the fish were removed, from September 2015 to August 2016. washed and dried and then stored in These species included Mulloidichthys plastic vials until being examined and flavolineatus (n=152), Mulloidichthys photographed. vanicolensis (n=21), and Parupeneus forsskali (n=102). For all individuals, Figure 1: Map showing the study area at Hurghada, Egypt. Figure 2: Proximal view of the left sagitta of common goatfish species from the Red Sea, Egypt. 817 Osman et al., Use of otolithic morphometrics and ultrastructure for… Morphometric and shape analysis of (otolith variables=aTLb), followed by otoliths log transformation to estimate a and b For morphometric analysis, the otoliths via simple linear regression, in which a from the left side of the fish were is the angular coefficient characterizing oriented with the inner side (sulcus the otolith’s growth rate and b is a acusticus) upwards and the rostrum to constant specific to the species. the right, for digitization using a To describe otolith shape, six stereomicroscope linked to a digital dimensionless shape factors (aspect camera (Optica 2.1) (Fig. 2). Then, ratio (AS), compactness (CO), form otolith length (OL, mm), otolith width factor (FF), rectangularity (RE), (OWid, mm), otolith area (OA, mm2), roundness (RO), and ellipticity (EL) and otolith perimeter (OP, mm) were were obtained by combining size measured using ImageJ software. parameters (Russ, 1990; Tuset et al., Otolith weight (OW, mg) was measured 2003b; Pinkerton, 2015) (Table 1). using an AS220 kL-1 model balance. The relationships between fish total length (TL) and otolith variables were estimated using the power equation Table 1: Otoliths shape indices. Index Formula Aspect ratio (AS) (OWid / OL) Compactness (CO) (OP2 / OA) Form factor (FF) 4 π OA / Op2 Rectangularity (RE) OA / (L * l) Roundness (RO) 4 OA / π L2 Ellipticity (EL) (OL - OWid) / (OL + OWid) OL, otolith length, OWid-otolith width, OA- otolith area, OP- otolith perimeter. Scanning electron microscopy mode and on a Stereo Scan Cambridge The otoliths were physically cleaned by Mark 2A (15 KV) at the Assiut carefully removing any adhering tissue University Electron Microscope Center, and debris without damaging the scale Assiut, Egypt. The morphological surface. Then, they were immersed in a descriptions of the otoliths were based solution of sodium hypochlorite for on the terminology proposed by Tuset several minutes to soften adhering et al., (2008) (Fig. 2). tissues for further cleaning. For scanning electron microscopy (SEM) Statistical analysis examination, the otoliths were fixed on A Kolmogorov-Smirnov test was used a specimen holder using sticker tape to check the normality of the data and coated with a 30-nm layer of gold. distributions and variance homogeneity. Electron micrographs were produced on Statistical description of the weight, a GAOL, GSMS 400 LV scanning length and otolith size of goatfish from electron microscope in back-scattering the Red Sea was conducted using SPSS. Iranian Journal of Fisheries Sciences 19(2) 2020 818 A paired sample t-test was employed to descriptive statistics (minimum, compare the left and right otoliths maximum, mean, standard error and (SPSS, Version 18). Summaries of the standard deviation) and paired-t tests descriptive statistics for the otolith are shown in Table 2. An insignificant shape indices of common species of difference (p>0.05) in the weight, family Mullidae were performed using length, width, area, and perimeter of the SPSS. A power equation was applied to otoliths was observed between the left estimate the interaction between fish and right sagittal pairs for each goatfish length and otolithic measurements. species (Table 2). Therefore, the left otoliths were selected for the recording Results of other measurements