Postflexion Larvae Research Articles

Notes on the morphology of the early stage of the rare bramid genus Eumegistus

The morphology of the early stage of Eumegistus was described from three specimens [E. brevorti: 23.0 mm in standard length (SL) juvenile; E. illustris: 5.8 mm SL postflexion larva, and 40.0 mm SL juvenile] recently rediscovered in museum collections. Larval and juvenile pigmentation patterns were reported for the first time for this genus. The 5.8 mm SL postflexion larva of E. illustris had pigmentation on the head and anterior half of the body, through to the middle of the dorsal fin base. In larvae and juveniles of both species, the outer side of the pelvic fin was pigmented. The two juveniles possessed several spines on the lachrymal and protruding rays in the middle of the caudal fin. Although it is known previously that the notochord flexion occurs at 5.0–6.0 mm SL in E. brevorti, the reexamined 5.0 mm SL specimen had the notochord completely flexed. Furthermore, we could not confirm whether the previously studied 4.0 mm SL specimen was E. brevorti because it was badly damaged.

Diel and tidal variations in larval fish exchange in the mouth region of the Gamtoos Estuary, South Africa

Diel and tidal variations in density of larval fishes were monitored over one neap and one spring tidal cycle in the mouth region of the warm temperate Gamtoos Estuary, South Africa. Data were collected over two 24h periods, using mixed method sampling with WP2 nets and a pushnet to sample both channel and margin waters. Larval fishes collected included 20 species from 12 families. Density varied with tide and diel state during the study period, with significantly higher catches recorded on the spring tide. Density of larval fishes peaked after the onset of darkness, predominantly associated with the nocturnal ebb tide. Large numbers of preflexion gobiid larvae were recorded on this tide state, this behaviour serving to facilitate movement out of the estuary for gobies that undergo a marine phase in their development. Spatial variations in larval fish distribution were also noted. Preflexion larvae were caught mainly in mid-channel waters, whilst postflexion larvae were more often encountered in the slower-flowing marginal waters. Data for a hydrodynamic model of tidal exchange of fish larvae in the estuary mouth region were collected concurrently with sampling and were used to model exchange of larval fishes over the neap and spring tidal cycle by extrapolating actual densities, using modelled tidal volume. Findings suggest that for some species, tidal exchange could escalate to millions of individuals over a single tidal cycle.

Larval development of Symphurus atramentatus (Cynoglossidae: Pleuronectiformes) from the Gulf of California

Symphurus atramentatus is described from larval to juvenile stages based on 30 specimens from the Gulf of California. Eleven larvae (preflexion, flexion, and postflexion) and three juveniles were cleared and stained to obtain the number of proximal dorsal-fin pterygiophores in each of the anterior first five interneural spaces and the number of hypural elements. Meristic features were nine precaudal vertebrae, 49–51 total vertebrae, 91–97 dorsal rays, 75–79 anal rays, 12 caudal rays, and four hypural elements. All specimens had a 1-3-3-2-2 ID pattern. The combination of these characterstics confirm that the specimens belong to Symphurus atramentatus. Pigmentation pattern of S. atramentatus from preflexion to postflexion stage consists of one dashed line of pigments on the base of the anal fin pterigiophores. In posflexion larvae, a dashed line of pigments appears on the base of the anal rays, on the dorsal margin of the body, on the lateral midline of the body, in the base of the first 15 dorsal rays, and on the base of the last 25 dorsal rays. In preflexion larvae, the ventral margin of the intestine had three or four blotches, which coalesce to form a continuous dotted line in postflexion larvae. Five elongated dorsal fin rays are present from preflexion to postflexion stages, which in the juvenile stage had a similar size with the rest of the adjacent rays.

Developmental morphology of the cyprinid fish Chela dadiburjori

Embryonic, larval, and juvenile development of an Indian cyprinid fish, Chela dadiburjori, is described from laboratory-reared specimens. The eggs, measuring 0.7–0.9 mm in diameter, were demersal, almost spherical in shape, transparent and unpigmented, with a pale yellow yolk and no oil globule. Hatching occurred 50–61 h after fertilization at ca. 27°C. The newly hatched larvae, measuring 2.4–2.6 mm in body length (BL), had melanophores on the body with 14–16 + 14–17 = 29–31 myomeres. Two dark transverse bands on the ventral body surface and one melanophore on the lower margin of the eye in newly hatched larvae were diagnostic. Additionally, a cement organ for adhering to objects was present on the forehead of yolk sac larvae <3.1 mm BL. The yolk was completely absorbed at 3.5 mm BL. Notochord flexion was initiated at 5.0 mm BL and finished at 6.0 mm BL. Aggregate numbers of all fin rays were completed at 9.2 mm BL. Squamation was initiated on the caudal peduncle at 8.0 mm BL and completed at 10 mm BL. The eggs of C. dadiburjori resembled those of the closely related species Devario malabaricus and Danio rerio. The larvae and juveniles of C. dadiburjori were also similar to those of the latter species in general morphology, especially the presence of body melanophores in newly hatched individuals and a distinctive lateral streak on the head during the period from yolk sac to postflexion larvae. However, early yolk sac larvae of C. dadiburjori were more similar to those of Devario malabaricus than Danio rerio in having a cement organ on the forehead. Larvae and juveniles of C. dadiburjori differed from those of the latter two species in pigmentation on the ventral body surface at hatching and around the mouth during the period from preflexion to early postflexion larvae and in having a dark lateral streak or band on the body in postflexion larvae and juveniles.

Ontogeny of tolerance to hypoxia and oxygen consumption of larval and juvenile red sea bream, Pagrus major

Changes in tolerance to hypoxic stress and oxygen consumption were studied in the red sea bream, Pagrus major, from its early life stage until 42 days post-hatch. In the experiments, metamorphosis was observed mainly from days 15 to 30, and the morphological shift from larva to juvenile was completed at around 9.5 mm total length (TL). During the larval stage, lethally low dissolved oxygen (DO) levels and mass-specific metabolic rates increased with growth from 2.6 to 5 mm TL ( P<0.01). Subsequently, the levels remained high and decreased until about 9.5 mm TL around the flexion stage and post flexion stage. Finally, beginning in the juvenile stage, lethal DO levels and mass-specific metabolic rates decreased as TL increased up to about 30 mm ( P<0.01). The relationship between lethal DO levels and mass-specific metabolic rates was significantly linear ( r=0.59, p<0.001, n=207) in fish larvae and juveniles. These results indicated that, around the stage of flexion and post flexion larvae in red sea bream, metabolic rates were highest during metamorphosis, and consequently hypoxia tolerance was lowest. It was presumed that the increasing metabolic rate during metamorphosis induced a decrease in the metabolic scope of activity and thereby induced the decrease of the tolerance to some environmental stressors in the background.

Uncisudis posteropelvis, a new species of barracudina (Aulopiformes: Paralepididae) from the western North Pacific Ocean

Six specimens (2 flexion larvae: 9.5–10.4 mm in notochord length; 4 postflexion larvae: 12.3–18.2 mm in standard length) collected from the western North Pacific are tentatively ascribed to the genus Uncisudis of the tribe Lestidiini of the subfamily Paralepidinae (Paralepididae) in sharing remarkably elongate and filamentous pelvic fin rays, their tips reaching the origin of the anal fin. They are described as Uncisudis posteropelvis sp. nov. in uniquely having the insertion of pelvic fins closer to the origin of anal fin than to the posterior end of dorsal fin base among lestidiine species. Addition to this character, the new species has remarkably elongate and filamentous dorsal fin rays, the short distance between anus and origin of anal fin (4.2–6.1% of standard length, SL), the posteriorly located pelvic fins (prepelvic length 69.4–71.5% SL), dorsal fin rays 10, anal fin rays 28–29, myomeres 41–42 + 38–40 = 80–81 (vertebrae 38 + 41 = 79), and peritoneal pigment spots 11–12. The occurrence of larvae differing in pigment pattern from the present new species suggests another undescribed species of Uncisudis in the western South Pacific.

Larvae of Arnoglossus elongatus (Pleuronectiformes: Bothidae) from northwestern Australia

Eleven postflexion larvae (9.1–23.9 mm standard length: SL) of a bothid, Arnoglossus elongatus, from northwestern Australian waters were described. These specimens were characterized by vertebral numbers of 11 − 12 + 32 − 34 = 43 − 45, slender body, remarkably elongated second dorsal fin ray, and presence of melanophores on and slightly above midlateral line of body, plus on dorsal wall of abdominal cavity and air bladder (specimens >12.6 mm SL), proximally on caudal fin rays (>16.5 mm SL), and on pterygiophore zones of dorsal fin and anal fin (>23.8 mm SL).

Larval development and food habits of the marbled parrotfish, Leptoscarus vaigiensis , associated with drifting algae

The larval development and food habits of the marbled parrotfish, Leptoscarus vaigiensis (Scaridae) associated with drifting algae were studied. In this study, 628 L. vaigiensis of various developmental stages ranging from postflexion larvae (9.4 mm in standard length, SL) to adults (192.0 mm SL) were sampled from drifting algae at two fishing ports in Nakagusuku Bay of Okinawa Island. In 3969 fish comprising 65 taxa in 34 families of Teleostei collected with drifting algae, L. vaigiensis occupied 15.8% of samples and occurred generally throughout the whole year. A large number of L. vaigiensis were collected from July to October accompanied by an occurrence of drifting algae composed of Sargassum spp. Larvae and early juveniles ranging from 11.1 to 14.9 mm SL appeared sporadically throughout the year, and postflexion larvae ≪11 mm SL occurred from July to November. Their food shifted from planktonic copepods in postflexion larvae and juveniles ranging from 10.0 to 14.9 mm SL to seaweed in the juveniles ranging from 15.0 to 24.9 mm SL. Furthermore, adults and young over 25 mm SL fed almost exclusively on seaweed, with Sargassum spp. constituting the drifting algae. These facts indicate that drifting algae may have a role concerning food and habitat, and may act as a nursery for L. vaigiensis.

Feeding pattern and the visual light environment in myctophid fish larvae

The trophic spectrum and feeding pattern of two myctophid larvae, Benthosema glaciale and Myctophum punctatum, were analysed in relation to changes in daily light intensity. The larvae of both species live relatively deep, occurring in the first 100 m, though distribution of M. punctatum extends to 150 m depth. The present study, carried out in the western Mediterranean (Alboran Sea), indicated that the larvae of the two species exhibit different foraging strategies. Both started to feed at dawn, but while feeding of M. punctatum was high at dawn and dusk, the feeding of B. glaciale remained high throughout the day. The light intensity profiles taken during the day indicated that at the depths where the species dwelt, light intensity was enough to provoke a feeding response. The larvae of these species, in contrast to the majority of fish larvae, had an enhanced sensitivity due to their pure rod‐like retina, an adaptation for foraging at low light intensities. Both species showed an ontogenetic change in their diet: B. glaciale preflexion larvae fed mainly on copepod eggs and nauplii, while postflexion larvae consumed calanoid copepodites; M. punctatum larvae showed a more diversified diet, composed of larger prey items. The stalked and elongated eye of M. punctatum larvae would enable the detection of a greater range of prey in terms of shape and size. In addition, the retina of this species was characterized by a higher summation ratio and longer photoreceptors, indicating a preference for dimmer environments. This could explain the decreasing feeding activity of M. punctatum during the high light intensity of the middle daylight hours. As a clear relationship existed between feeding pattern and light intensity in these myctophid larvae, the visual characteristics of each species could help to explain the different strategies of foraging behaviour, therefore avoiding a possible overlap in their trophic niche.

Habitat use by larval fishes in a temperate South African surf zone

Larval fishes were sampled in the Kwaaihoek surf zone on the south east coast of South Africa. On six occasions between February and May 2002, larval fishes were collected in two habitat types identified in the inner surf zone using a modified beach-seine net. The surf zone habitats were classified as either sheltered trough areas or adjacent exposed surf areas. Temperature, depth and current measurements were taken at all sites. Trough habitats consisted of a depression in surf topography characterised by reduced current velocities and greater average depth than adjacent surf areas. In total, 325 larval fishes were collected. Of these, 229 were collected in trough and 96 in surf habitats. At least 22 families and 37 species were represented in the catch. Dominant families were the Mugilidae, Sparidae, Atherinidae, and Engraulidae. Dominant species included Liza tricuspidens and Liza richardsonii (Mugilidae), Rhabdosargus holubi and Sarpa salpa (Sparidae), Atherina breviceps (Atherinidae) and Engraulis japonicus (Engraulide). Mean CPUE of postflexion larvae of estuary-dependent species was significantly greater in trough areas. The proportion of postflexion larval fishes in trough habitat was significantly greater than that of preflexion stages, a result that was not apparent in surf habitat sampled. CPUE of postflexion larvae of estuary-dependent fishes was negatively correlated with current magnitude and positively correlated with habitat depth. Mean body length of larval fishes was significantly greater in trough than in surf habitats. These results provide evidence that the CPUE of postflexion larvae of estuary-dependent fishes is higher in trough habitat in the surf zone and this may be indicative of active habitat selection for areas of reduced current velocity/wave action. The implications of this behaviour for estuarine recruitment processes are discussed.

Description of Larval Cynoglossus Zanzibarensis (Teleostei: Cynoglossidae) from the Tsitsikamma Coast, South Africa

The early development and the temporal distribution of Cynoglossus zanzibarensis larvae are described, based on specimens collected along the Tsitsikamma coast, South Africa. The yolk sac is evident in larvae of up to 3.4 mm body length (BL). There are 46–57 (6−9 + 37−50) myomeres and the gut extends to 37, 36 and 31% BL in preflexion, flexion and postflexion larvae respectively. Flexion is initiated by 5.6 mm BL and is complete in all larvae >7.8 mm BL. Two elongate dorsal fin rays are visible by 3.5 mm BL, and a single medial pelvic fin bud appears by 6.2 mm BL. Eye migration is initiated in larvae >7.0 mm BL and complete by 11.6 mm BL. Pigment is concentrated over the ventral and lateral gut area, as well as along the dorsal and ventral trunk and tail surfaces. Lateral tail pigment becomes heavier in postflexion larvae. The larvae of C. zanzibarensis are compared with previously described tonguefish species, including the congeneric C. capensis, which has fewer dorsal and anal fin rays (D103–110, A81–88 compared with D116–124, A92–103), 2–4 elongate dorsal rays compared with 2 and a larger size at flexion (9.9 mm BL compared with 6.6 mm BL).

Do the characteristics of the ichthyoplankton in an artificial and a natural entrance channel of a large estuary differ?

The Peel-Harvey Estuary in south-western Australia became so eutrophic in the 1970s and 1980s that a radical approach was adopted in order to increase tidal exchange between this estuary and the ocean and thereby flush greater volumes of nutrients out to sea. This involved constructing a deep artificial (Dawesville) channel between the estuary and the ocean, at a location ca. 15 km south of the shallower and natural (Mandurah) channel. Samples of fish larvae were collected monthly throughout 1997 to determine whether the characteristics of the ichthyoplankton on flood and ebb tides differed within and between channels and whether they underwent the same types of intra-annual changes in the two channels. In both channels, the number of species and concentration of larvae were both significantly greater on flood than ebb tides and the species composition differed significantly between tides. The concentrations of larvae were at their greatest, by far, between early spring and early autumn. Flood and ebb tides in both channels were dominated by the goby Favonigobius lateralis, which was transported out on ebb tides as preflexion larvae and subsequently brought back on flood tides as postflexion larvae. The larvae of Hyperlophus vittatus, Pseudorhombus jenynsii and Rhabdosargus sarba, which spawn outside the estuary, were far more abundant on flood than ebb tides, whereas the reverse pertained with Atherinosoma elongata, Apogon rueppellii and Pseudogobius olorum, which spawn within the estuary. In contrast to the situation with the diversity and concentration of larvae, the species composition on both flood and ebb tides differed significantly between channels. However, the latter differences were small and mainly due to relatively greater numbers of larval F. lateralis on ebb tides in the Mandurah Channel and the very occasional occurrence of reef species on flood tides in the Dawesville Channel. During the year, the species composition underwent cyclical changes on both tides and in both channels, due to out of phase sequential monthly changes in the concentrations of certain species.

Larval and juvenile development of the medusafish, Icichthys lockingtoni (Perciformes: Centrolophidae), from the Northwest Pacific, and a comparison with Northeast Pacific larval and juvenile forms

Larval and juvenile development of Icichthys lockingtoni are described and illustrated based on specimens collected off northeastern Japan. Some osteological characters are detailed, and comparisons are made with previous descriptions from the Northeast Pacific. Postflexion larvae (11.7–15.4 mm BL) had small preopercular spines; juveniles (19.5–42.2 mm BL) had weakly serrated outer margins of the preopercle, interopercle, and subopercle. In late juveniles (about 40 mm BL), the second and third epurals fused, the epurals thereafter comprising two elements.

Larvae of two pleuronectiforms, Poecilopsetta plinthus (Poecilopsettidae) and Parabothus coarctatus (Bothidae), from southern Japan

Pelagic larvae of two pleuronectiforms, Poecilopsetta plinthus (Poecilopsettidae) and Parabothus coarctatus (Bothidae), are described and illustrated based on specimens collected off Tosa Bay, southern Japan. Postflexion larvae (8.2–11.9 mm BL) of Poecilopsetta plinthus are characteristic in having a series of melanophore patches along the dorsal and anal fin bases and the inner margins of the pterygiophore zones, and linear myoseptal pigmentation also along the inner margins of the latter. Preflexion and flexion larvae (5.0–6.3 mm BL) of Parabothus coarctatus are distinctive in having the dorsal fin origin located level with the dorsal margin of the eye and seven elongated rays in the anterior part of that fin.

Jaw development and malformation in cultured striped trumpeter Latris lineata

Intensive culture of striped trumpeter ( Latris lineata) has resulted in a high incidence of jaw malformation in juveniles. In this study, cranial and jaw development in striped trumpeter was described in cultured larvae reared in greenwater on rotifers and Artemia. Jaw malformation was only evident in post-flexion larvae greater than the standard length of 10 mm and was characterised by an open jaw in which the maxilla and premaxilla were aligned dorso-ventrally, and the anterior hyoid arch elements were in an abnormal ventral position. X-radiography of the heads of juvenile and adult cultured striped trumpeter revealed ventro-lateral distortion of the jaw elements in comparison with wild-caught fish. The possible role of physical environmental factors and nutrition during culture are discussed in relation to jaw malformation in this and other species.

Description of a postflexion larva specimen of Liopropoma japonicum from off Izu Peninsula, Japan

Description of a postflexion larva specimen of Liopropoma japonicum from off Izu Peninsula, Japan

The Surf Zone Ichthyoplankton Adjacent to an Intermittently Open Estuary, with Evidence of Recruitment during Marine Overwash Events

The composition, structure and seasonality of ichthyoplankton in the surf zone adjacent to the mouth of the intermittently open East Kleinemonde Estuary (33°32′S, 27°03′E) were investigated over a period of 2 years. Altogether 451 fishes, representing at least 21 taxa from 14 families, were collected. The assemblage was dominated by postflexion larvae of euryhaline marine species that are dependent on estuaries as nursery areas. The sparid Rhabdosargus holubi was the most abundant taxon and constituted more than 77% of the total catch. A distinct modal size class was identified forR. holubi , while the mean individual size of this and other abundant taxa was comparable to the observed recruitment size range reported from a wide variety of estuarine nursery habitats in southern Africa. Periodic regression analyses revealed significant peaks in abundance of larval R. holubi during late winter (August), at down and dusk, at new and full moon (spring tides), and on the flood stage of the tidal cycle. Evidence for estuarine immigration during marine overwash events (surging rough seas that enter the estuary) is provided by (1) the stranding of postflexion larvae in the region of the closed estuary mouth following these events, and (2) back extrapolation from length modes within the estuary to coincide with such an event. The advantages and disadvantages of such a recruitment strategy are discussed.

Food and feeding ecology of Brazilian sardine (Sardinella brasiliensis) larvae from the southeastern Brazilian Bight

Results from depth integrated and vertically stratified plankton samples collected in the southeastern Brazilian Bight were used to study the feeding behavior of Brazilian sardine (Sardinella brasiliensis) larvae. Sampling of the ichthyoplankton was carried out with 60 cm Bongo nets in the Bight during the spawning seasons of 1991/92 and 1992/93. The sampling of microzooplankton was carried out in the coastal region off Ubatuba, using the closing-type plankton net, in December 1995. The feeding study was based on a total of 901 captured larvae. Gut content analysis of the sardine larvae showed a diurnal pattern of food intake. Copepod nauplii dominated the diet of the preflexion and flexion larvae, but they were the second in abundance for the postflexion larvae which fed preferentially on copepodites and adults of Oncaea spp. Averaged feeding incidence of the 901 larvae was 37.6%, but it increased to 58.5% for day-caught larvae. Seventy percent of the food particles were found in the mid-gut and food eaten showed a natural increase in digestion from fore-gut to hind-gut. Vertical distribution of microzooplankton revealed that copepod nauplii were present in densities of 10-20 ind. L-1, mainly in the upper mixed layer (0-20 m depth), but higher densities of copepodite and adult of Oncaea, Oithona and Paracalamis were found within and beneath the thermocline. These results show that Brazilian sardine larvae can successfully adapt their diet, feeding on the most abundant food particles in the upper mixed layer of the survey area.

Early life history of kitsune-mebaru, Sebastes vulpes (Scorpaenidae), in the Sea of Japan

The larval and juvenile stages of kitsune-mebaru,Sebastes vulpes, based on 50 wild specimens collected in, the Sea of Japan, are described and illustrated, and some ecological aspects of the early life history (feeding, horizonal distribution and habitat shift) included. Preflexion larvae became extruded between 3.9–4.6 mm body length (BL) and notochord flexion occurred between 4.7–7.1 mm BL. Transformation from postflexion larvae to pelagic juventiles occurred between 13–17 mm BL. Compared with other rockfish species,S. vulpes is deep-bodied, throughout both larval and, juvenile stages. Larval and juvenileS. vulpes inhabit mainly coastal water surface layer (usually on the continental shelf), but do not occur offshore region (northwest of Oki Islands). Although someS. vulpes juveniles are associated with drifting seaweed, such clumps are not indispensable habitats for any stages. Surface-to-benthie migration of juveniles occurs at about 25 mm BL. Preflexion and flexion larvae feed mainly on copepod nauplii, and postflexion, transforming larvae and pelagic juveniles mainly on calanoid copepodites (Parracalanus parvus).

Explaining advection: do larval bay anchovy (Anchoa mitchilli) show selective tidal-stream transport?

Schultz, E. T., Cowen, R. K., Lwiza, K. M. M., and Gospodarek, A. M. 2000. Explaining advection: do larval bay anchovy (Anchoa mitchilli) show selective tidalstream transport? – ICES Journal of Marine Science, 57: 360–371. Bay anchovy (Anchoa mitchilli) have been reported in several systems to display net up-estuary larval movements, against the mean flow. However, the means by which such transport occurs is poorly understood. We address how estuarine circulation and larval behaviors serve to transport larvae of the bay anchovy. In two successive summer seasons, we conducted multiple near-synoptic samples of larval distributions and water column structure along a 45-km section of the middle Hudson River estuary. The analysis focuses on patterns in the vertical distribution of larvae that may help explain transport, and the along-river distribution of different ontogenetic stages. The prediction that post-flexion larvae induce selective tidal-stream transport (STST) by vertically migrating in conjunction with tidal or diel cycles was tested via harmonic regression. Larval concentrations and average larval depths often varied with tidal stage. Maximum concentrations tended to occur at times of slack water, and larvae were often closer to the surface during slack tides as well. These patterns may be the result of tidal movements of horizontal abundance gradients, rather than vertical migrations. The prediction that larval transport is facilitated by a preference for deep water was addressed via analysis of variance, testing for depth effects on time-averaged concentration estimates. At some sites, larvae were most concentrated at intermediate depths, which would promote retention (no net horizontal movement) or slow up-river transport. However, in 1996, larvae were found most concentrated at the surface at two sites, suggesting down-river advection. With respect to along-river distribution, we tested the prediction that ontogenetic stages differed in their distribution in a manner consistent with up-river transport. In 1995, pre-flexion larvae were distributed further up river than eggs, and post-flexion larvae were slightly up river of pre-flexion larvae. Along-river distributions were perturbed in 1996 by a storm that caused high run-off and forced larvae down river. Following this event, along-river position did not vary with ontogenetic stage. The study design that combined analysis of larval depth distribution and along-river distribution enabled us to make and test predictions regarding transport processes. A portion of our depth distribution data implied stasis or weak up-river advection, and we found evidence that this was the case. 2000 International Council for the Exploration of the Sea