A comparative ontogenetic study of the tetraodontiform caudal complex

Konstantinidis P. and Johnson, G. D. 2012. A comparative ontogenetic study of the tetraodontiform caudal complex. —Acta Zoologica (Stockholm) 93 : 98–114. Interpretation of the caudal complex of adult Tetraodontiformes has proven problematic because of the consolidation of the component elements. Here, we show that an ontogenetic approach offers considerable elucidation of the homology of the caudal complex, resulting in a new understanding of the grundplan of these fishes. The reductions of structures of the caudal complex are interpreted in a phylogenetic context. The caudal skeleton of larval triacanthodids resembles that of many adult percomorphs; however, during subsequent development epural 3 disappears, while epural 2 is reduced so that it can hardly be distinguished from the uroneural remnants. Juvenile triacanthids have an epural 2 that is lost in ontogeny, and the cartilaginous parhypural becomes integrated into the large hypural plate. In ostraciids and diodontids, the parhypural is absent throughout development. The hypural plates of adult balistids, monacanthids and tetraodontids have a conspicuous diastema between the dorsal and ventral portions. However, in early stages of the former two, the dorsal and ventral portions are continuous in cartilage proximally and remain fused in the adults. In tetraodontids, the two hypurals are separate from their initial appearance in cartilage and never fuse, raising the question of homology of the individual hypurals among the different families.     

Osteological development in the Japanese sardine,Sardinops melanostictus

The development of all osteological elements, except scales, of the Japanese sardine,Sardinops melanostictus, is described from newly-hatched larvae to adult fishes. Newly-hatched larvae lacked osteological elements. Part of the head skeleton began to develop in 53 hour old larvae (4.2 mm in notochord length [NL]). Larvae at the first-feeding stage (77 hours, 5.5 mm NL) possessed several elements of the head skeleton and pectoral fin supports. In a 10.5 mm NL specimen, part of the caudal and dorsal fin supports were apparent. The centra appeared in specimens 18–22.7 mm in standard length (SL). Gill rakers were first observed in the lower branchial arches at 13 mm NL and spine-like processes with spiny nodules from about 25 mm SL. The distance between the predorsal and first dorsal proximal radial relative to SL rapidly decreased with forward translocation of the dorsal fin and became constant beyond approximately 34 mm SL. At this stage, most basic osteological elements were established. Completion of the osteological structure was characterized by the disappearance of the dentary teeth at 60–70 mm SL. Based on the osteological development, ontogenetic intervals consisting of four periods and eight phases were recognized.     

The hemiramphid,Oxyporhamphus, is a flyingfish (exocoetidae)

Osteological and myological studies on the caudal complex of flying fishes (Exocoetidae) plusOxyporhamphus (of Hemiramphidae) revealed the following shared derived conditions: 1) neural spines of preural vertebrae broader than haemal spines; 2) spur present on posterior margin of preural vertebra 2;3) upper hypural plates steeply angled; 4) lower hypural plate extending strongly posteriorly; 5) lower hypural plate deeply surrounded by caudal fin rays; 6) flexor ventralis well developed, arising from neural spines; 7) flexor ventralis externus well developed; 8) adductor dorsalis well developed.Oxyporhamphus and exocoetids also share a lower jaw of adults not elongate and the premaxilla with a straight anterior margin. Therefore,Oxyporhamphus is transferred to the Exocoetidae, with which it shares a total of 10 derived conditions.     

Juvenile development of a flathead,Suggrundus meerdervoortii (Scorpaeniformes: Platycephalidae)

Juvenile development ofSuggrundus meerdervoortii was described, based on twelve specimens (12.9–43.8 mm SL) collected from off Yamagata Prefecture, Japan Sea. Two exterior openings in the lateral line scales were completed at ca. 35 mm SL, with the interopercular flap and iris lappet being visible at ca. 44 mm SL, these all being useful taxonomic characters. In juveniles and additional young and adult specimens (ca. 70–191 mm SL), the proportions of head length, snout length, orbital diameter, caudal peduncle depth and caudal fin length decreased with growth; interorbital width decreased rapidly until ca. 70 mm SL, but more or less stabilised thereafter (70–191 mm SL).     

When two equals three: developmental osteology and homology of the caudal skeleton in carangid fishes (Perciformes: Carangidae)

Ontogeny often provides the most compelling evidence for primary homology in evolutionary developmental studies and is critical to interpreting complex structures in a phylogenetic context. As an example of this, we document the ontogenetic development of the caudal skeleton of Caranx crysos by examining a series of cleared and stained larval and postlarval specimens. By studying ontogeny, we are able to more accurately identify some elements of the adult caudal skeleton than is possible when studying the adult stage alone. The presence of two epurals has been used as a synapomorphy of Caranginae (homoplastically present in the scomberoidine genera Scomberoides and Oligoplites). Here we find that three epurals (ep) are present in larvae and small postlarval juveniles (i.e.,<25 mm standard length [SL]) of C. crysos and other carangines, but ep2 never ossifies and does not develop beyond its initial presence. Ep2 was last observed in a 33.6 mm SL specimen as a small nodule of very lightly stained cartilage cells and eventually disappears completely. Therefore, the two epurals present in the adult are ep1 and ep3. In other carangines examined (e.g., Selene, Selar), the rudimentary ep2 ossifies and appears to fuse to the proximal tip of ep1. In these taxa, therefore, the two epurals of the adult appear to be ep1+2 and ep3. We found no indication of three epurals at any stage in the development of Oligoplites (developmental material of Scomberoides was unavailable). We discuss the osteology of the caudal skeleton of carangoid fishes generally and emphasize the power and importance of ontogeny in the identification of primary homology.     

Osteological development of the vertebral column and of the caudal complex in Dentex dentex

Osteological development of the vertebral column and caudal complex in common dentex was described under extensive larval rearing conditions. Generally, the cartilaginous bones developed prior to the membranous bones. The development of the axial skeleton began with the formation of the hypural 1, the neural arches 2 and 3, as well as the haemal arches 1–8 at 4·8, 4·9 and 5·0 mm total length ( L _T, measured in vivo ), respectively. By 7·5 mm L _T, all the cartilaginous elements were formed, except for the ventral ribs, which formed between the range of 8·4–18·0 mm L _T. The caudal lepidotrichia were the first membranous bones to appear (5·3 mm L _T) and attain their full meristic count (7·4 mm L _T), followed by the vertebral centra, which formed between 6·6 and 9·7 mm L _T. By 25·0 mm L _T, all the elements were fully ossified except for the ventral ribs. The developmental direction and order of all the elements were studied with respect to their formation and ossification. The results were discussed in the contexts of ichthyoplankton, ecology and aquaculture. Compared with other Sparidae species, common dentex followed a pattern of relatively rapid rate of osteological development.     

Age and growth in a newly-established invasive population of topmouth gudgeon

Specimens of invasive topmouth gudgeon, Pseudorasbora parva, from Šúr Pond (Bratislava, Slovakia) were examined to assess age and growth, and to determine whether this recently-established invasive population employs a less specialized ontogenetic trajectory than the specialized form typical of native and/or long-time established populations. Samples were collected in October 2004 (n=143). Standard length (SL) ranged from 18.16 mm to 67.57 mm (mean 32.56 mm), and eviscerated body weight ranged from 0.10 to 5.02 g (mean 0.63 g). Scale caudal diameter ranged from 0.52 to 2.42 mm (mean 1.08 mm). SL at which the scales started to form was estimated to be 1.58 mm. The population was represented with 5 age groups, from 0+ to 4+. Relative to other populations for which comparable data are available the recently-established population of topmouth gudgeon was found to mature at smaller size and at a younger age compared to native and/or long-time established populations (all specimens bigger than 25.0 mm SL, and 94% of specimens from the age group I were already mature).     

Early development of fin-supports ani fin-rays in the milkfishChanos chanos

Development of fin-supports and fin-rays was observed in larval and juvenileChanos chanos, Chondrification of the caudal complex started at 4.70 mm SL. Ossification of the caudal elements started at 7.80 mm SL and was nearly completed at about 30 mm SL. Cartilaginous fusion of caudal elements, which occurs in hypurals of higher teleostean fishes but is not seen in lower teleosts, was observed between the neural arch of the preural centrum 1 and that of the ural centrum 1 via a small cartilage bridging the distal tips of the two arches. Caudal finrays began to develop at 6.60 mm SL, and an adult complement of principal rays was attained at 7.35 mm SL. Dorsal and anal pterygiophore elements were first evident at 6.70 mm and 6.65 mm SL, respectively. All proximal radiais were formed at 8.15 mm SL in both fins. Formation of dorsal and anal fin-rays started simultaneously at 8.60 mm SL, and adult fin-ray complements were attained at 10,00 mm and 10.70 mm SL, respectively. In the pectoral fin, the cleithrum, coraco-scapular cartilage and blade-like cartilage (fin plate) had already been formed at 4.65 mm SL. The mesocoracoid was observed to originate from the coraco-scapular cartilage and become detached from it in the course of ossification. Pectoral fin-ray formation started at 13.80 mm SL and was completed in number of rays at 20.00 mm SL. In the pelvic fin, the basipterygium was first evident at 13.00 mm SL. Pelvic fin-rays appeared at 13.80 mm SL and attained their adult count at 17.15 mm SL.     

Annual reproductive cycle and sexual dimorphism in the dragonet,repomucenus valenciennei, in tokyo bay, japan

The annual reproductive cycle of the dragonet,Repomucenus valenciennei, from Tokyo Bay, Japan, was studied by analysis of seasonal trends in gonadosomatic indices and histological observations of gonads. Sexual dimorphism in the growth of several body parts relative to standard length (SL) and changes in color pattern of the first dorsal fin with growth were also investigated. The spawning season lasted from spring (April [1991] or February [1992]) to autumn (October) with two spawning peaks, in spring and autumn. In spring, only one-year-old (age 1+) fish spawned, age 0+ females not spawning until autumn, at which time they had reached age 1+. Likewise, histological observations of males indicated that testes had reached full maturity by 80 mm SL (age 1+). The minimum mature size of females was estimated as 60 mm SL. In males 45–80 mm SL, the first spine of the first dorsal fin, last ray of the second dorsal fin, last ray of the anal fin, and caudal fin ray showed strongly positive allometry, indicating rapid growth of these structures relative to SL. Subsequently, their growth returned to an isometric pattern in males>80 mm SL. In females, on the other hand, the same body parts showed slightly positive allometry throughout their growth. The color pattern on the first dorsal fin also changed in males 45–80 mm SL.     

大黄鱼仔稚鱼脊柱、胸鳍及尾鳍骨骼系统的发育观察

研究采用二重染色法对3-28日龄人工培育的大黄鱼Larimichthys crocea(Richardson)仔稚鱼的部分骨骼系统的发育进行观察。结果显示,仔鱼的脊索从6日龄(平均全长MTL3.9mm)开始分节,8-10日龄髓弓、脉弓先后开始发育,14日龄(MTL7.5mm)脊椎骨、髓棘、脉棘均已形成,至28日龄(MTL19.5mm)已发生骨化;大黄鱼仔鱼孵化时,胸鳍的上匙骨、匙骨、后匙骨、支鳍骨原基已形成,27日龄(MTL19.0mm)稚鱼具5块支鳍骨,鳍条发育完整;尾鳍发育以8日龄仔鱼脊索后端腹部2块尾下骨的形成开始,至14日龄仔鱼尾鳍已初具雏形,尾杆骨、尾上骨和尾下骨均发育完全,21日龄稚鱼尾下骨排列成弧状,第三与第四块尾下骨之间的缝隙增大,把尾鳍鳍条分为上下两部分,鳍条分节明显,28日龄稚鱼尾鳍尾杆骨及鳍条发生钙化。       

Histochemical study of jaw muscle fibers in the American alligator (Alligator mississippiensis)

The ontogenetic development of caudal vertebrae and associated skeletal elements of salmonids provides information about sequence of ossification and origin of bones that can be considered as a model for other teleosts. The ossification of elements forming the caudal skeleton follows the same sequence, independent of size and age at first appearance. Dermal bones like principal caudal rays ossify earlier than chondral bones; among dermal bones, the middle principal caudal rays ossify before the ventral and dorsal ones. Among chondral bones, the ventral hypural 1 and parhypural ossify first, followed by hypural 2 and by the ventral spine of preural centrum 2. The ossification of the dorsal chondral elements starts later than that of ventral ones. Three elements participate in the formation of a caudal vertebra: paired basidorsal and basiventral arcocentra, chordacentrum, and autocentrum; appearance of cartilaginous arcocentra precedes that of the mineralized basiventral chordacentrum, and that of the perichordal ossification of the autocentrum. Each ural centrum is mainly formed by arcocentral and chordacentrum. The autocentrum is irregularly present or absent. Some ural centra are formed only by a chordacentrum. This pattern of vertebral formation characterizes basal teleosts and primitive extant teleosts such as elopomorphs, osteoglossomorphs, and salmonids. The diural caudal skeleton is redefined as having two independent ural chordacentra plus their arcocentra, or two ural chordacentra plus their autocentra and arococentra, or only two ural chordacentra. A polyural caudal skeleton is identified by more than two ural centra, variably formed as given for the diural condition. The two ural centra of primitive teleosts may result from early fusion of ural centra 1 and 2 and of ural centra 3 and 4, or 3, 4, and 5 (e.g., elopomorphs), respectively. The two centra may corespond to ural centrum 2 and 4 only (e.g., salmonids). Additionally, ural centra 1 and 3 may be lost during the evolution of teleosts. Additional ural centra form late in ontogeny in advanced salmonids, resulting in a secondary polyural caudal skeleton. The hypural, which is a haemal spine of a ural centrum, results by growth and ossification of a single basiventral ural arococentrum and its haemal spine. The proximal part of the hypural always includes part of the ventral ural arcocentrum. The uroneural is a modification of a ural neural arch, which is demonstrated by a cartilaginous precursor. The stegural of salmonids and esocids originates from only one paired cartilaginous dorsal arcocentrum that grows anteriorly by a perichondral basal ossification and an anterodorsal membranous ossification. The true epurals of teleosts are detached neural spines of preural and ural neural arches as shown by developmental series; they are homologous to the neural spines of anterior vertebrae. Free epurals without any indication of connection with the dorsal arococentra are considered herein as an advanced state of the epural. Caudal distal radials originate from the cartilaginous distal portion of neural and haemal spines of preural and ural (epurals and hypurals) vertebrae. Therefore, they result from distal growth of the cartilaginous spines and hypurals. Cartilaginous plates that support rays are the result of modifications of the plates of connective tissue at the posterior end of hypurals (e.g., between hypurals 2 and 3 in salmonids) and first preural haemal spines, or from the distal growth of cartilaginous spines (e.g., epural plates in Thymallus). Among salmonids, conditions of the caudal skeleton such as the progressive loss of cartilaginous portions of the arcocentra, the progressive fusion between the perichondral ossification of arcocentra and autocentra, the broadening of the neural spines, the enlargement and interdigitation of the stegural, and other features provide evidence that Prosopium and Thymallus are the most primitive, and that Oncorhynchus and Salmo are the most advanced salmonids respectively. This interpretation supports the current hypothesis of phylogenetic relationships of salmonids. © 1992 Wiley-Liss, Inc.     

Schistura sexnubes, a new diminutive river loach from the upper Mekong basin,Yunnan Province,China (Teleostei：Cypriniformes：Nemacheilidae)

An ichthyofaunistic survey of Mekong tributaries in Lincang Prefecture, Yunnan Province, China yielded a new species of nemacheilid loach, herein described as Schistura sexnubes species nova. The new species is readily distinguishable from its congeners by the following combination of characters: 8+8 branched caudal fin rays, an incomplete lateral line, a dissociated caudal bar, a shallow caudal peduncle depth (7.6%-9.6% SL; respectively caudal peduncle 1.76-1.95 times longer than deep), a diminutive size of less than 50 mm SL, and no sexual dimorphism. A dorsocephalic pattern consisting of a black, forward directed V-shaped formation located between the nares, and a white, ovoid blotch on the upper operculum serves as an autapomorphy.     

Reproduction and early development of a freshwater pipefish <Emphasis Type="Italic">Microphis leiaspis</Emphasis> in Okinawa-jima Island,Japan

We investigated the size at maturation, breeding season, and morphological development of larvae and juveniles of a freshwater pipefish Microphis leiaspis, which belongs to Gastrophori, collected from three rivers on the northern part of Okinawa-jima Island, Japan. The minimum size of brooding males was 105–123 mm in standard length (SL). The smallest mature female was estimated to be ca. 130 mm SL from the analysis of gonadosomatic index (GSI) and histological observations of gonads. The breeding season was estimated to be from June to December according to monthly changes in female GSI, histological observations of gonads, and monthly changes in the occurrence of brooding males. The number of eggs in the male brood pouch ranged from 75 to 241 (mean ± SD: 152 ± 52, n = 22). The male releases newly hatched larvae in freshwater areas. After newborns grow in the sea, they return to freshwater areas of the rivers and attain maturity. Microphis leiaspis was conformed to have an amphidromous life history. Notochord length of the released larvae was 6.1 mm, with a well-developed finfold. Larvae attained 11.1 mm SL, formation of the caudal and dorsal fin rays was complete, and the caudal fin became lozenge shaped at 30 days after the release, and juveniles reached 36.0 mm SL at 63 days after release. In the period between 30 and 63 days after the release, formation of all fins except the pectoral fins was completed, and caudal fin rays were extended and sector shaped with deep slits between each fin ray. The morphology of the released larvae of M. leiaspis is similar to that of Gastrophori species, and the morphology of juveniles similar to other species of Microphis.     

Juveniles of Kyphosus vaigiensis (Quoy and Gaimard 1825) with reference to a senior synonym of Cantharus lineolatus Valenciennes 1830

The juveniles of Kyphosus vaigiensis (Quoy and Gaimard 1825), collected from the Indian Ocean and Japanese waters, are described with some ontogenetic morphological changes based on six specimens having 14 dorsal and 13 anal fin soft rays, 56–62 scales in a longitudinal row along the midbody, and 30–32 gill-rakers on the first gill-arch. The juveniles of K. vaigiensis smaller than ca. 42 mm in standard length (SL) have the proximal parts of the dorsal and anal fin soft-rayed portions covered with small scales, and the single outer row of the upper jaw teeth consisting of incisor-like and conically pointed teeth, the former with polycuspid tips differing from the specimens greater than ca. 68 mm SL. The holotype of Cantharus lineolatus Valenciennes 1830, 41.5 mm SL, was included here in the juveniles as K. vaigiensis. Therefore, K. vaigiensis is recognized as a senior synonym of C. lineolatus.     

Larvae and juveniles of the plunderfishes <Emphasis Type="Italic">Artedidraco shackletoni</Emphasis> and <Emphasis Type="Italic">A.</Emphasis><Emphasis Type="Italic">skottsbergi</Emphasis> (Notothenioidei,Artedidraconidae) from the Indian sector of the Southern Ocean

Early life stages of Artedidraco skottsbergi and A. shackletoni were collected off Adélie Land. The morphology and pigmentation pattern of nine larvae and juveniles of A. skottsbergi between 17.2 and 21.4 mm in standard length (SL), and of two juveniles of A. shackletoni measuring 25.1 mm SL were described. A. skottsbergi was characterized by a heavily pigmented body, except for the caudal peduncle, with distinctively dense pigmentation on the ventrolateral half of the body and caudal section (17.2–17.9 mm SL). Furthermore, they had no pigmentation on the pectoral fin base until they attained 21.4 mm SL. Juvenile A. shackletoni had a heavily pigmented body except for the ventral side of the abdomen and the anal fin base. The proximal part of the dorsal fin and most of the anal fin were covered with melanophores. Although knowledge of larval and juvenile Artedidraco species is limited, the distribution of melanophores on the fins, pectoral fin base and caudal peduncle at each developmental stage may be useful for species identification.     

Larval and juvenile Polymetme elongata (Stomiiformes: Phosichthyidae) collected from Suruga Bay and offshore waters, Japan

Two larvae [17.4 mm standard length: SL (postflexion stage)] and 26.1 mm SL (transformation stage)] and a juvenile (31.7 mm SL) of a phosichthyid, Polymetme elongata, from Suruga Bay and offshore waters, central Japan, are described. These specimens had an elongate body with relatively short preanal length (53–63% SL), long anal fin base (2.6–3.4 times dorsal fin base length), and anal fin origin below dorsal fin base, and were further characterized by a blackish flap on each eye and internal clusters of melanophores (e.g., along caudal myosepta around midlateral line and on ventral margin of caudal peduncle). The short preanal length and larval melanophore pattern were very similar to those of another phosichthyid, Yarrella blackfordi, from the Atlantic Ocean.     

A description of the smallest Triodon on record (Teleostei: Tetraodontiformes: Triodontidae)

The smallest known specimen (20mm standard length: SL) of Triodon macropterus Lesson is described and illustrated. It is easily distinguished from superficially similar tetraodontid and diodontid larvae or early juveniles of comparable size by the following characters: separate premaxillae in conjunction with the fused dentaries; the presence of multicuspid spinoid scales; the jet-black mark in front of the soft dorsal fin; the developing pelvis, which is visible through the distended skin of the belly; and the presence of a number of procurrent caudal fin rays. The small Triodon differs from the adult in possessing a huge head that measures 45% SL (vs. 28.5–32.7% in adult), the absence of the characteristic dewlap with the conspicuous lateral ocellus, and the structure of the scales and nostrils.     

Description of juvenile development ofArtediellus neyelovi (cottidae) from off Usujiri, southern Hokkaido, Japan

Juveniles ofArtediellus neyelovi are described on the basis of 24 specimens (8.3–23.6 mm SL) from Hokkaido, Japan. All medial and paired fins were completely developed in all specimens. The smallest specimen (8.3 mm SL) had a slender elongated suborbital stay similar to that of adults. Specimens 8.3–10.1 mm SL had 4 preopercular spines, cirri absent on the head and body, except a very small supraorbital cirrus, and sensory canals comprising open grooves restricted to the head surface. Specimens 14.1–20.0 mm SL had complete cephalic sensory canals, and the 2nd and 3rd preopercular spines reduced. Specimens 20.8–23.6 mm SL had a nearly complete lateral line canal and exhibited most specific diagnostic characters except some cephalic cirri. The anterior 3 neural arches on both sides were separate at 8.3 mm SL, but had become fused (except for the anteriormost) at 14.3 mm SL. The anteriormost arch was not fused in an adult, 71.3 mm SL. Some juveniles had very reduced bony plates under the skin anterodorsally on the body, which were not present in adults.     

Juveniles of two sillaginids,Sillago aeolus andS. sihama,occurring in a surf zone in the Philippines

Sillaginid juveniles collected from the surf zone at Tigbauan, Iloilo, Philippines, between May 1986 and September 1987 were identified asSillago aeolus (n=702, 8.9–26.0 mm SL) andS. sihama (n=3414, 8.6–22.9 mm SL), based on the numbers of dorsal and anal soft fin rays and vertebrae. The two species were easily distinguishable by the pattern of melanophores distributed on the caudal fin base,S. aeolus having a triangular-shaped cluster, whereas the melanophores formed a vertical line inS. sihama. The ratios of pre-anal and caudal peduncle lengths to SL also differed between the species, both being higher inS. aeolus. The occurrence ofS. aeolus was limited to the dry season, from January to March. On the other hand,S. sihama occurred year-round, although a peak was observed in the dry season, from November to April.     

Redescription of a rare deepwater cardinalfish, Epigonus ctenolepis Mochizuki and Shirakihara 1983, and comparison with related species (Perciformes: Epigonidae)

A rare epigonid fish, Epigonus ctenolepis Mochizuki and Shirakihara 1983, is redescribed in detail on the basis of two type specimens (90.0??8.0?mm standard length, SL) and an additional specimen (128.8?mm SL) collected from Suruga Bay, Japan, and compared with related species of Epigonus. The species is characterized by the following combination of characters: first dorsal-fin rays VII, second dorsal-fin rays I, 9??0, vertebrae 10?+?15, pored lateral-line scales 52??3 (hypural end 48??9?+?caudal fin 4), pyloric caeca 9??1, total gill rakers 24??5, presence of a pungent opercular spine, lateral-line scales ctenoid, absence of a maxillary mustache-like process, and absence of a rib on the last abdominal vertebra. A key to the Epigonus species characterized by a pungent opercular spine is provided.