Catfish species are considered an important group in freshwater and brackish water environments. They constitute a significant proportion of the inland fisheries of several countries, and therefore, several catfish species have been reared. Several species are also significant for the aquarium industry and represent a substantial sector in the world aquarium trade (Teugels 1996).
Catfish species are broadly spread and occur on all continents. Among the different families of catfish, Ariidae and Plotosidae are the only marine taxa, while others are all freshwater fish (Roxo et al. 2014). The skeletal system of catfish is distinguished by joint-locking pectoral- and dorsal fin spines. The shared features of these fin spines among the different species of catfish may hint at their early phylogenetic origin (Fine et al. 1997; Sullivan et al. 2006; Lundberg et al. 2014).
The wahrindi,
The golden Nile catfish
From an anatomical point of view, the catfish spine embodies a link between the lepidotrichia and the spines of acanthopterygian fishes. The difference occurs in how these constituents are combined into a single assembly (Reed 1924). The lepidotrichia, which supports the growth of the spine, first looks like an expansion of the basement membrane as in the occurrence of soft rays designated by Harrison (Harrison 1893; Goodrich 1904).
The significance of the morphology of the dorsal spines of catfish species is apparent from identifying both extant and fossilised specimens, as most of the catfish fossils have dorsal spines, which are strong and fossilised well. Their shape has been used to differentiate families or genera (Gayet & Van Neer 1990; Greenwood 1959) but not species.
Consequently, the taxonomic value of variation in fin spine structure is essential for understanding the sonic behaviour of different catfish based on variances in their spine morphology. The taxonomic significance of spine morphology in catfish has long been known. The building of spines has been valuable for recognising and distinguishing between catfish species and even some higher groups (Gayet & Van Neer 1990; Rodiles-Hernández et al. 2010; Egge & Simon 2011).
The present study provides a standard morphological description for the dorsal fin spine of three catfish species collected from the Nile River and Lake Nasser in Egypt,
The specimens of
In all species, the dorsal spine is an elongate, compressed, tapered, slightly arched, osseous structure, bearing a series of retrorse dentations along the anterior and posterior surfaces and has a sharp sagittate tip. The retrorse, anterior dentations are most pronounced in the upper third of the spine and gradually alter in form until they appear as a series of distinct notches on the basal third of the spine. The anterolateral surfaces of the dorsal spine are marked by numerous short, irregular, shallow, anastomosing, longitudinal furrows. Located along the posterior margin of the spine, a shallow groove gradually deepens and broadens toward the base of the spine. Lying within this groove are posterior dentations, which, at about the level of the junctions of the basal and middle thirds of the spine, gradually increase in size and then abruptly terminate near the inferior margin of the distal opening of the central canal. The posterior surface of the sagittate tip, superior to the first posterior dentation, is flattened and set at an angle which contains the distal opening of the central canal of the spine. The rear spine gradually broadens to the basal third and then abruptly expands into the triangular-like articulation. The proximal opening of the central canal is located at the upper apex of the triangular base. Inserting a fine wire through the proximal opening of the central canal indicates that the canal extends throughout the entire spine length, and the wire can be removed from the distal opening. Immediately beneath the proximal opening of the central canal is a median foramen, which receives the ring-like articulation of the second interneural spine. The articulating portion of the dorsal spine’s base comprises three condyles, a large median, and a small lateral condyle on either side.
The median foramen is small and rounded in shape (Figs. 2, 3). In
The shape of the articular head is triangular in all species. It comprises three parts, two wings, usually rounded edges, and a broad middle section. In
In
The crest of the spine is usually provided with ornamentations. In
The ratio of the articular head’s width to the spine’s width at its base ranges from 1.10 in
The posterior surface of the median crest has no grooves, but small tubercles are present in small individuals of
In three species (
Regarding the effect of pollution on the morphology of the dorsal fin spine in the localities from which species were collected, no abnormalities were recorded in any species examined.
The general morphology of the spine of the dorsal fin of the three catfish species examined in this study agrees with the description given by Alexander (1966). Most catfish have large spines in their dorsal fin. Similar spines occur in quite a variety of other fish, for instance,
Some spine-bearing catfish are too large, when adult, to be in danger of predation by other fish, but the spines must protect them while young. Some catfish have evolved poison glands associated with their spines (Bhimachar 1944; Norman & Greenwood 1963; Fine & Ladich 2003; Bosher et al. 2006).
The size and type of ornamentations found on the surface of the dorsal fin spine are variable due to the size of the fish and the species.
Changes in the surface morphology and structure of the spine were noticed in individuals from both the families examined, Claroteidae and Mochokidae. Considerable variations were also seen in the morphology of the dorsal fin spine within a small range of fish size for different individuals of the three species. The rapid growth of the dorsal spine prepares it as a weapon essential for the fish’s survival (Alexander 1966). The Claroteidae and Mochokidae are considered venomous (Fine & Ladich 2003), and both individuals depend on the spines of their dorsal and pectoral fins to be used as weapons. Therefore, they need rapid growth of these spines in a short time, but there are also growth changes in the dorsal fin spines of these species. The present results showed that the growth period of the dorsal spine for
The shape of the dorsal fin spine differs between
Features of the dorsal-fin spine of
Characters | 200 – 400 mm TL, n = 10 | 401 – 600 mm TL, n = 10 |
---|---|---|
Median foramen, shape and size | Small, rounded, with dorsal edge | Large, rounded, with course ridges dorsally |
Shape of the articular head | Triangular in shape, with the middle part has rounded lower edge, higher than the wings which have rounded edges and well-separated from the middle part. | Triangular in shape, with middle part broad, rounded and larger than wings. Rounded wings, well-separated from the middle part |
Presence or absence of striations on the lateral sides of the spine, their shape and size | Presence of a shallow striations traversing over most of the length of the spine and diminish towards the tip. | Deep and irregular striations diminish towards the tip of the spine |
Ornamentations on crest | Presence of an irregular ridges along the length of the crest | Presence of an irregular dentations getting larger towards the tip of the spine and irregularly separated |
Ratio of width of the articular head/width of the spine at its base | 1.82 | 2.65 |
Ratio of the width of the median foramen/width of the articular head | 0.15 | 0.05 |
Average angle made by the lateral border of each wing of the articular head with the corresponding lateral border in ventral view | 114° | 137.7° |
Posterior surface of the median crest | Presence of an irregular pores along the length of the median crest. | Presence of curved down dentations getting larger towards the tip of the spine |
Posterior blocking processes | Well-developed, broad, with curved posterior edge directed posteriorly | Well-developed, with straight edge directed posteriorly |
Features of the dorsal-fin spine of
Characters | 100 – 200 mm TL, n = 10 | 201 – 300 mm TL, n = 10 | 301 – 400 mm TL, n = 10 |
---|---|---|---|
Median foramen, shape and size | Small, rounded, with no edges | Large, rounded, with high edges | Large, oval, with high edges |
Shape of the articular head | Triangular in shape. The middle part is narrow and levelled with the wings, which are separated from the middle part by shallow grooves | Triangular in shape, with middle part is levelled with the wings. No grooves | Triangular in shape. Broad middle part, with edges and deep grooves separating it from the wings. The middle part is higher than the wings |
Presence or absence of striations on the lateral sides of the spine, their shape and size | No striations are present on the sides of the spine | Deep striations present towards the posterior edge of the spine and shallow anteriorly. Diminish towards the tip of the spine. | |
Ornamentations on crest | Smooth, no ornamentations | Mainly smooth, with slight irregularities in the surface near the head | Presence of a few tubercles irregularly arranged near the articular head and smooth on the remaining surface of the crest. They are variable in size. |
Ratio of width of the articular head/width of the spine at its base | 1.46 | 2.0 | 1.74 |
Ratio of the width of the median foramen/ width of the articular head | 0.15 | 0.13 | 0.14 |
Average angle made by the lateral border of each wing of the articular head with the corresponding lateral border in ventral view | 119° | 101.5° | 109° |
Posterior surface of the median crest | No grooves. Tubercles are small | Presence of shallow grooves and tubercles getting larger towards the tip of the spine | Presence of deep grooves, tubercles getting larger towards the tip of the spine |
Posterior blocking processes | Poorly developed directed posteriorly | Well-developed, pointed directed laterally | Broad, well-developed, posteriorly directed. |
Features of the dorsal-fin spine of
Characters | 200 – 250 mm TL, n = 10 | 251 – 300 mm TL, n = 10 | 301 – 350 mm TL, n = 10 | 351 – 400 mm TL, n = 10 |
---|---|---|---|---|
Median foramen, shape and size | Small, rounded, with high edges at dorsal side | Large, elongated dorsal ventrally, with ridges at the dorsal side | Small, rounded, with low edges | Large, rounded, with high edges |
Shape of the articular head | Triangular in shape. The middle part broad and wider than the wings. Rounded edged wings, with notch at their lateral base | Triangular in shape. The middle part with rounded edges and shorter than the wings. The left wing with triangular left head and rounded right head. | Triangular in shape. The middle part broad. The wings with rounded edges. Presence of deep groove separating middle part and the wings. | Triangular in shape. The middle part broad levelled with wings. Presence of a deep groove separating wings and the middle part. |
Presence or absence of striations on the lateral sides of the spine, their shape and size | Presence of a shallow striations diminish towards the tip of the spine | Presence of a deep striations at the lateral sides decrease in number towards the tip of the spine. | Presence of a deep curved striations decrease in number towards the tip of the spine. | |
Ornamentations on crest | Presence of a small sized tubercles confined to the anterior base of the spine | Smooth, with longitudinal keel traversing over the length of the spine | Smooth, with slight irregularities near the articular head. | Irregular surface, with no tubercles. |
Ratio of width of the articular head/width of the spine at its base | 1.7 | 1.14 | 1.9 | 2.3 |
Ratio of the width of the median foramen/width of the articular head | 0.1 | 0.08 | 0.29 | 0.27 |
Average angle made by the lateral border of each wing of the articular head with the corresponding lateral border in ventral view | 134° | 122° | 127.5° | 138° |
Posterior surface of the median crest | Presence of a shallow groove, with curved dentations getting larger towards the tip of the spine | Presence of a deep groove, with long and curved dentations getting longer towards the tip of the spine. Regularly spaced. | Presence of a deep groove, with large and dentations curved downward. Large dentations located near the tip of the spine. | |
Posterior blocking processes | Broad, not produced directed posteriorly | Broad, not produced, with wavy edge directed posteriorly. | Broad, not produced and directed posteriorly. |
In the dorsal spine growth of the species
Wide variations in the morphology of the dorsal spines of claroteid and mochokid individuals were investigated. These differences are represented in the following set of characters: the shape and size of the median foramen, the shape of the articular head, the shape of the ornamentations on the crest, the ratio of the width of the articular head to the width of the spine at its base, the ratio of the width of the median foramen to the width of the articular head, the average angle made by the lateral border of each wing of the articular head with the corresponding lateral border in ventral view, and the shape of the posterior surface of the median crest. Gayet & Van Neer (1990) also observed such differences in the morphology of the dorsal spine of some African silurid fish species and Pinton et al. (2006) on some species of the genus
During the present work, it was possible to distinguish two groups of characters of the dorsal fins spines features: (1) exclusive characters that clearly define a taxonomic group (genus or species); (2) characters that are shared by several genera, but that may be useful to define certain species within a genus. These features are, therefore, valid for the taxonomic identification of the catfish species investigated, but they need to be checked for indicating any phylogenetic signals.