The current study compared the premaxillary, dentary, neurocranium, otolith, vertebral and caudal bone for differentiating five ariid catfishes.
Premaxillary bone of ariid catfishes
It is a paired bone; the tooth is present only in the premaxillary bone so it is also called a toothed bone (Fig 2).
Arius arius
Feather shaped narrow sized bone, the caudal process is narrow with a blunt edge, Pair of premaxillary connected through the U shape bridge.
Osteogeneiosus militaries
The caudal process is short and sharp, the Pair of premaxillary connected through T shaped bridge and also a gap between two sides very less compared to
Arius arius
Nemapteryx caelata
Caudal process is long and sharp, the premaxillary process also extended up to the edge of caudal process, it looks like a small spatula, Pair of premaxillary connected through the large hump like continued step, Ascending and Articular process parallel to each other.
Plicofollis layardi
Fan feather shaped broader sized bone, Premaxillary process is short and broad, the Pair of premaxillary connected through cup or U shape bridge.
Netuma thalassina
Saw shaped, it also a short and sharp but lower side of the caudal process having minute innumerable blades. Pair of premaxillary connected through the small hump, the premaxillary process connected elevated structure.
Dentary bone of ariid catfishes
A pair of dentary forms the anterior part of the lower jaw (Fig 3).
Arius arius
A pair of dentaries forms the frontal part of the lower jaw. The size of the dentary bone is long and broad. The origin of the coronoid process and ventral process are the same, but the coronoid starts narrow it ends with a broad edge. The mental foramen is absent. meckelian fossa is broad. The length of the sensory canal is large.
Osteogeneiosus militaries
The size of the dentary bone is short and narrow. There are 3 numbers of mental foramen present. The length of the sensory canal is short. The coronoid process starts narrow it ends with a broad edge, but compared to
Arius arius it is large, it formed the V shape.
Nemapteryx caelata
The size of the dentary bone is very long and broad. The mental foramen is absent. The length of the sensory canal is large.
Netuma thalassina
It is too sharp and narrow. There are 2 numbers of mental foramen present. The sensory canal is not clearly visible. Meckalian fossa short and straight. Mental foramen is absent.
Plicofollis layardi
The size of the dentary bone is short and broad. Only one mental foramen present.
Neurocranium bone of ariid catfishes
The neurocranium comprises four parts constituting the major portion of the skull. Namely, they are the olfactory region, orbital region, Otic region and Occipital region (Fig 1-4) and (Table 1-7).
The vertebral column of the Ariid catfishes
The number of vertebral bones present in the vertebral column is one of the significant osteological key characters to discriminate the catfish species (Fig 1 and 6).
Arius arius
There are forty-two numbers of vertebral bones present in the vertebral column of
Arius arius among which 1
st six ventral side bones are reduced. In the mid portion, six vertebral bones are bifurcated.
Plicofollis layardi
There are fifty-two numbers of vertebral bones present in the vertebral column of
Plicofollis layardi among which the 6
th to 10
th ventral side bones are reduced. In the mid portion, dorsal side of the vertebral bone elongated, the ventral side was reduced and also the seven bones vertebral bones are bifurcated.
Netuma thalassina
There are forty-five numbers of vertebral bones present in the vertebral column of
Netuma thalassina among which 1
st 5 bone ventral side bones are reduced. Posterior side eight numbers of vertebral bones are equally reduced. Nine numbers of vertebral bones are bifurcated in the mid portion of vertebral column.
Osteogenus military
There are forty-seven numbers of vertebral bones present in the vertebral columun of
Osteogenus militaris among which only one ventral side bones are reduced. In the mid portion, five or six vertebral bones are bifurcated.
Nemapteryx caelata
There are fifty numbers of vertebral bones present in the vertebral columun of
Nemapteryx cealata. No reduced bone. In the mid portion, five numbers of vertebral bones are bifurcated.
Caudal bone of the ariid catfishes
The caudal bone comprises of uroneural, hypural, parlendural or parhypural or preural flange, neural spine and hemal spine. Among these uroneural, hypural and parlendural bones were mainly used as the primary character of differentiating the ariid catfishes (Fig 1-6).
Arius arius
The
Arius arius has three hypural bones, third hypural bones are shorter than the others. Parelandural bones are shortened and narrowed. Uroneural bones are Paired bones, they are connected to the hypural bones, size is large and somewhat broader bone.
Netuma thalassina
The
Netuma thalassina has three hypural bones, among these first and second bones are broader. Parelandural bones are narrowed. Uroneural are thin and shorter bone.
Nemapteryx caelata
The
Nemapteryx cealata has three hypural bones, third hypural bones are broader than the others. Parelandural bones are broader compared to others except for
Osteogeneiosus militaris. Uronerural are thick and larger bones.
Plicofollis layardi
The
Plicofollis layardi has four hypural bones, third and four hypural bones are larger than the others. Parelandural bones are thin and medium sized. Uroneural are thin and larger bones.
Osteogeneiosus militaris
The
Osteogeneiosus militaris has three hypural bones, third hypural bones are broader than the others. There is no demarcation between the first and second hypural bones. Parelandural bones are large and broader. Uroneural are large and broader bones except for
Nemapteryx cealata.
Otolith morphology study of ariid catfishes
Generally, ariid catfishes otoliths are circular, thick and bulbous in shape. All five different catfish species of otolith have similarities because they were from the same family but had enough differences to be distinguished from each other. The shape of the otolith is also used to differentiate catfishes from other groups of fishes. It has been divided into 4 regions they are distal, dorsal, proximal and ventral among these regions distal and ventral portions are used for otolith morphological identification (Fig 6).
Arius arius
The distal portion is long and straight. The ventral portion is V-shaped.
Netuma thalassina
The distal portion is short and straight. The ventral portion is broad and U shaped.
Plicofollis layardi
The distal portion is long and slanting. The ventral portion is broad and circular shaped.
Nemapteryx caelata
The distal portion is larger in size and its end portion is hook-shaped. The ventral is half-moon shaped.
Osteogeneiosus militaris
The distal portion is large in size. The ventral portion is bowl-shaped.
Catfish head skeleton one of the key character used for identification of marine catfishes
(Arratia, 2003).
Tilak (1965) described the Lateral ethmoid of
A.
bilineatus species are backside bulged which was helpful for eye protection. The head shield of
A.
dussumieri is generally the more rugose, having a broader, more granulated supraoccipital process than does
A.
bilineatus (Tilak, 1965).
Kailola (1986) explained the count of free vertebrae in
A.
thalassinus and
A.
bilineatus is an important discriminating feature of the identification of species.
Al-Hassan et al., (1988) enlightened that there are differences in the spines and neurocranium of Ariid catfish species. They also found that the snout of
A.
thalassinusis significantly sharper than that of the other Gulf catfish which is clearly viewed ventrally.
Rodrigues et al., 2020 discovered that sequence of thoracic and caudal bone similar in all the order of siluriform, in which the differences were found in only the vertebral bone number in the vertebral column of the catfishes. The vertebral column plays a major role in swimming and propulsion
(Laerm 1976;
Lindsey 1978;
Weihs 1989). Vertebral counts also aid in the identification of closely related taxa such as species of clupeids
(Houde et al., 1974). The intraspecific variation in vertebral counts must be known when using this character to separate closely related taxa
(Berry and Richards 1973).
Weitzman (1962) also explained the total number of vertebrae varies according to the fish species which may be lower or higher than certain taxa.
Licar-Rodrigues et al., (2020) demonstrated descriptions of the osteology of
S.
couma, which assisted to the area of taxonomy in fish.
Bemvenuti (2005) explicated that
Odontesthes bonariensis species having high number of precaudal bone than tail region.
Serra and Langeani (2006) highlights the occurrence of hypural in the caudal fin that vary and such variation is detected in the caudal fin of
S.
couma. A high number of hypural bones is often taken as a primitive character (
i.
e., seven in Elops and salmonids); reduction is advanced (
i.
e., four in pleuronectids). The hypural bones may be variously fused, ultimately into a single plate in adults of some species,
e.
g., Coryphaena
(Potthoff 1980). When fusion of hypural bones occurs, it may be observed in ontogeny in some fishes (
e.
g.,
Thunnus atlanticus,
Potthoff 1975; Coryphaena,
Potthoff 1980) but not in others (
e.
g.,
Ophichthus gomesi,
Leiby (1979);
Microgadus proximus,
Matarese et al., (1981). Uroneurals, paired bones generally occurring dorso laterally to the ultimate vertebra, are often the first bones to ossify in the caudal complex. According to
Patterson (1968), they are modified ural neural arches.
Javadzadeh et al., (2014) studied the otolith of
A.
dussumieri and
A.
thalassinus, different species from the same family can have similarities in appearance but have enough differences to be distinguished from each other. The otolith of sea catfish
Bagre panamensis is a large, compressed, thick circle with a well-developed rostrum
(Maldonado-Coyac et al., 2021). The shapes of an otolith morphology from four species of catfishes are basically having similarities in their presence
(Chen et al., 2010). The Goat fishes otolith morphology can be used to distinguish species and genera
(Echreshavi et al., 2021).
However, the present study supports earlier osteological studies and describe a additional key characters for catfish identification. Ariid catfish species identified by using various osteological key characteristics such as premaxillary, dentary, neurocranium, otolith, vertebral and caudal bone. Each bone structure varies with different fish species which will help to contribute to osteology as one of the important taxonomic tools for discriminating the ariid catfishes.
