Myomere Counts Research Articles

Descriptive morphology of the eggs, larvae, and juveniles of two cyprinid fishes belonging to the Zacco temminckii species' group

Embryonic, larval, and juvenile development of two cyprinid species belonging to the Zacco temminckii species' group, Z. temminckii (Temminck and Schlegel) and Zacco sp. (type A), are described and compared with each other from laboratory-reared and wild specimens. The eggs of both species were closely similar except in diameter [1.92–2.20 mm in Z. temminckii vs. 1.60–1.75 mm in Z. sp. (type A)], being demersal, almost spherical in shape, transparent and unpigmented, with a pale yellow yolk, and no oil globule. Hatching occurred 40–53 h after fertilization in Z. temminckii and after 47–60 h in Z. sp. (type A). The newly hatched larvae of both species [4.9–5.3 mm in body length (BL) in Z. temminckii and 3.5–4.8 mm BL in Z. sp. (type A)] also resembled each other, having a large transparent pear-shaped yolk and lacking body pigmentation. Myomere counts of Z. temminckii and Z. sp. (type A) larvae and juveniles were 24–27 + 14–17 = 41–42 and 23–27 + 14–17 = 40–41, respectively. The yolk was completely absorbed at 8.3 mm BL in Z. temminckii and at 6.6 mm BL in Z. sp. (type A). Notochord flexion was initiated and completed at 7.8 mm BL and 8.2 mm BL in Z. temminckii and at 6.3 mm BL and 6.6 mm BL in Z. sp. (type A), respectively. Aggregate numbers of all fin rays were completed at 17 mm BL in Z. temminckii and 13 mm BL in Z. sp. (type A). Although the morphology of larvae and juveniles of both species was very similar, differences in body length of each developmental stage, the duration and process of disappearance of the adipose finfold, the anal fin ray counts, and pigmentation on the lateral body surface were clearly recognized.

The Distribution and Ecology of Ariosoma Balearicum (Congridae) Leptocephali in the Western North Atlantic

A total of 4589 leptocephali of the congrid eel, Ariosoma balearicum, were examined from 17 cruises in the western North Atlantic Ocean. Myomere counts made on 915 of these indicated there were two ranges of number of myomeres that appear to be associated with separate spawning populations. Those with the higher range (high count: 128–137) were consistently 70–100 mm in length in the Sargasso Sea from February to April and 20–80 mm in length in the northern Sargasso Sea and Gulf Stream from September to October. Those with the lower range (low count: 120–130) were rare in the northern and eastern Sargasso Sea where they had consistently greater lengths than high count leptocephali and were most abundant in the Florida Current and Providence Channel. The geographic distributions of size and myomere ranges in relation to hydrography provide strong support for the hypothesis that high count eels found along the South Atlantic Bight (SAB) migrate across the Florida Current to spawn in the northwest Sargasso Sea. This migratory pattern is similar to those of Anguilla rostrata and Conger oceanicus, which use the southern Sargasso Sea for development as larvae. However, the distribution of high count leptocephali suggests that they use the entire Sargasso Sea gyre as a development area as larvae before crossing the Florida Current and recruiting to the SAB. The low count eels inhabiting the Bahamas appear to spawn near the banks and their abundance in the Providence Channel and southwest Sargasso Sea suggests most are retained close to the Bahamas. These two distinct styles of spawning, distribution and recruitment of larvae are hypothesized to be related to the different hydrographic regimes of the two juvenile habitats and the resulting constraints on growth and recruitment of larvae. Vertebral and myomere counts reported from other areas suggest there are distinct populations in other regions of the North Atlantic Ocean.

Examining Similarities and Differences between Congeners: Do Larval Gizzard Shad and Threadfin Shad Act as Ecologically Equivalent Units?

Abstract Although adult gizzard shad and threadfin shad differ both morphologically and ecologically, their larvae appear quite similar, and myomere counts are required to distinguish them. Because little previous work has distinguished between the larvae of these species, little is known about how their larvae interact with each other or with other members of the aquatic community. In two Alabama impoundments, larval gizzard shad appeared in the limnetic zone before larval threadfin shad, after which they co-occurred for up to 6 weeks. The relationship between mouth gape and fish length was positive and similar for both species. Diets of larvae in both lakes were similar between species, consisting primarily of small prey (i.e., zooplankton eggs, rotifers, and copepod nauplii) in eutrophic Weiss Lake and larger crustacean zooplankton (calanoid and cyclopoid copepods, copepod nauplii, and Diaphanosoma spp.) in mesotrophic Lake Martin. For both species, prey types became more diverse with fish length, and ...

Ontogeny of the Darter Subgenus Doration with Comments on Intrasubgeneric Relationships

The darter subgenus Doration has been considered a monophyletic group within the Boleosoma complex. Previous workers combined Etheostoma stigmaeum, the speckled darter, and Etheostomajessiae, the blueside darter, and recognized a single species with several subspecies. Recognition of E. stigmaeum and E. jessiae as distinct species is warranted based on early life-history characters. Etheostoma stigmaeum can be distinguished from E. jessiae by postanal melanophore pattern, precocious ontogenetic development, position of melanophores, and length at which fin elements develop. Etheostoma stigmaeum possesses radiating melanophores at every postanal myoseptum, whereas E. jessiae has several distinct melanophores at the future anal-fin insertion; E. stigmaeum develops fin elements at smaller sizes than E. jessiae. Early lifehistory attributes of Doration are egg-burying, possession of a single, midventral vitelline vein, elevated (18) preanal myomere counts, and absence of pigmentation from the dorsal and lateral body. Larval and early-juvenile apomorphies of Doration include the following: possession of small egg diameters (1.3-1.7 mm); pointed snout; oval-spherical eye shape; small head length/TL; moderate predorsal length/ TL; small pectoral-fin length/TL; narrow shoulder depth/TL; narrow midpostanal depth/TL; laterally compressed, rectangular yolksac; precocious notochord flexion; five predorsal myomeres; 18 presoft dorsal myomeres; 10 preoperculomandibular pores; and presence of midlateral pigmentation.

Larval development of laboratory-reared carpenter,Argyrozona argyrozona(Pisces: Sparidae)

The larval development of the sparid Argyrozona argyrozona is described and illustrated from 16 individuals, representative of a batch reared in the laboratory from artificially spawned eggs. A general account of development is given as well as detailed descriptions of pigmentation, fin development, head spination, myomere counts and morphometries. The general developmental pattern is similar to other sparids but is unique in regard to preopercular spination, premaxillary and medio-lateral pigmentation and morphometries.

Emigrating larvae of koaro,Galaxias brevipinnisGünther (Teleostei: Galaxiidae), from the Otira River, New Zealand

Abstract Fish larvae were collected in stream benthic invertebrate drift nets from the Otira River, near Arthur's Pass, New Zealand during a study of benthic drift. They are identified as probably those of koaro (Galaxias brevipinnis Gunther) on the basis of estimates of myomere counts (indicating Galaxiidae or Retropinnidae); by a process of elimination of likely species on the basis of distance up stream, elevation, and habitat characteristics; and by determining fish species in the Otira River tributaries upstream of the sampling location. This comprises the first likely record of emigrating larvae of koaro, a species known to be diadromous by the return migrations from the sea of whitebait juveniles during spring. A newly hatched larva of koaro is described and figured.

Life History of the Savannah Darter, Etheostoma fricksium, in the Savannah River Drainage, South Carolina

Etheostomafricksium is endemic to the Savannah, Broad, Combahee, and Edisto river drainages on the Coastal Plain in South Carolina and Georgia. In Tinker Creek, South Carolina, a third-order blackwater stream, E. fricksium was most common in medium to moderately fast current over sandy substrates in association with woody debris, undercut banks, or eel grass. Males and females matured at 1 yr. Nuptial males had bright red-orange and green lateral bars and small tubercles on anal fin rays. Mean clutch size was 26, and there was indirect evidence of multiple clutch production. Spawning was from Feb.-May at water temperatures of 11-23 C. Aquarium-held spawning adults buried eggs in sand and fine gravel. Eggs (mean diameter = 1.7 mm) hatched in 6-11 days at 22 C. Larvae had large melanophores on top of the head and two rows of melanophores on the dorsum; modal myomere counts were 16 preanal, 22 postanal, and 38 total. Early growth was rapid, and males grew faster than females. The largest male and female were 55 and 50 mm SL, respectively. Females outlived males, attaining a maximum age of 49 mo and outnumbered males 1.5:1. Chironomid larvae numerically dominated the diet of all size classes but were replaced by heptageniid (Stenonema) nymphs as the volumetrically dominant food item in larger darters. Life histories were compared between E. fricksium and other species of Belophlox to identify variable traits that may help to resolve their phylogenetic relationships.

Spatial and Temporal Heterogeneity of Larval Shad in a Large Impoundment

Factors that affect recruitment of threadfin shad Dorosoma petenense and gizzard shad D. cepedianum, two important prey species in southern reservoirs, are not well understood. Larval shad typically have not been identified to species, though interactions between shad larvae likely affect their recruitment and that of their predators. Using myomere counts to identify larval shad to species, we quantified spatial and temporal variation in species distributions in West Point Reservoir, Alabama–Georgia. We sampled larvae every 3–4 d at three distances from shore (inshore and 25 and 50 m offshore) at each of three sites. Larval threadfin shad migrated offshore in all three sites, whereas larval gizzard shad were evenly distributed across distances from shore. Because of these movement differences, larval gizzard shad and larval threadfin shad may encounter different habitat-specific predation rates, climatic effects, and food availability. In addition, larval gizzard shad were present before larval threadfin shad and grew beyond the size vulnerable to our capture techniques before threadfin shad abundance peaked. If zooplankton densities are reduced by young-of-year shad, as documented in other systems, later-hatched threadfin shad would encounter fewer zooplankton than were available to the earlier larval gizzard shad. Threadfin shad would have reduced growth and greater vulnerability to predation and starvation.

Morphological variation among widely dispersed larval populations of anadromous southern hemisphere lampreys (Geotriidae and Mordaciidae)

Larvae of all three southern hemisphere anadromous parasitic lampreys were collected from rivers in Australia, New Zealand and South America. Body intervals were measured, trunk myomeres counted and the frequency of pigmentation in different body regions recorded. Morphometric data were subjected to multiple group principal components analysis (MGPCA) which took into account changes during growth. The components (together with myomere counts) and the pigmentation data were both subjected to discriminant analysis. Ordination and rank correlation tests revealed no evidence for either latitudinal clines or a continuum of circumpolar change amongst larval lamprey populations. Clustering of population centroids clearly distinguished between Mordacia lapicida (Gray) from Chile and M. mordax (Richardson) from south-eastern Australia. Populations of Geotria australis Gray divided into groups representing three geographical regions, namely Argentina, Chile and Australasia (Western Australia, Tasmania and New Zealand). Ammocoetes from Argentina were the most divergent, possessing a more posterior cloaca, taller dorsal fins, a greater gap between dorsal fins, and distinctive pigmentation on the head and caudal fin. Within the Australasian group, Western Australian and New Zealand populations clustered closer than either did with those from Tasmania. The cluster analyses for larval populations of G. australis suggest that, during their marine trophic phase, the adults of this species originating from Argentinian and Chilean rivers follow different migratory routes, whereas those from Western Australia, New Zealand and, to a lesser extent, Tasmania intermix.

Early Development of the Blue Sucker, Cycleptus elongatus

Cycleptus elongatus, a large-river catostomid of the southeastern and central United States, was artifically spawned from broodstock taken from the Alabama River in Alabama. Larvae were reared to the juvenile stage. Posthatching ontogeny of larvae of Cycleptus is similar to that reported for other catostomids. Distinguishing characteristics for protolarval blue suckers are preanal and total myomere counts, pigment pattern, dorsal origin of the median fin fold, ratio of eye diameter to head length, and sizes at particular stages of development. The blue sucker in later phases of development is distinguishable from other catostomids by numbers of preanal and total myomeres and length of dorsal fin.

Contributions of Developmental Characters to a Phylogeny of Catostomid Fishes, with Comments on Heterochrony

Characteristics of larval stages were examined to develop a hypothesis of evolutionary relationships among living catostomid fishes for comparison with adult-based hypotheses. The final set of 30 characters included morphometric measures, myomere counts, relative timing of developmental events and presence of distinctive pigmentation. In all, 17 species representing all but 2 of 11 extant genera were included. Hypotheses were constructed using cladistic principles with character polarity established by cyprinid outgroup comparison. The best estimate of phylogeny based on the observed character states was similar to adult-based concepts of relationships. Subfamilies and tribes sorted well, but developmental characters did not demonstrate monophyly of these taxa. Ictiobines were most primitive. The catostomine tribe Erimyzontini was not recognized; Erimyzon was allied with the ictiobines and Minytrema with Moxostoma.

Geographic and Temporal Variation in Numbers of Myomeres in Fish Larvae from the Lower Mississippi River

There was statistically significant geographic and temporal variation in numbers of myomeres in larval freshwater drum Aplodinotus grunniens, river carpsucker Carpiodes carpio, and bluegill Lepomis macrochirus collected throughout the 1978 spawning season from the Mississippi River at Eudora, Arkansas, and St. Francisville, Louisiana. The mean number of total myomeres in each species usually was higher at St. Francisville than 400 river kilometers north at Eudora. Freshwater drum larvae at Eudora had fewest myomeres during periods of warmer water temperatures; freshwater drums at St. Francisville, and river carpsuckers and bluegills at both locations, had either stable or fluctuating myomere counts as the season progressed. Such variation in diagnostic characters should be accounted for when local or regional keys are constructed for fish larvae.

Identification of Catostomid Larvae in Pyramid Lake and the Truckee River, Nevada

Abstract As adults, mountain suckers Catostomus platyrhynchus inhabit the Truckee River, Tahoe suckers Catostomus tahoensis both the river and Pyramid Lake, and the endangered cui-ui Chasmistes cujus the lake only, except during the spawning season. All spawn in the river and under certain conditions the latter two species also spawn in the lake. Diagnostic characters useful in identifying most larvae and early juveniles include differences in pigmentation, size at the onset of specific developmental events, and gut and mouth morphologies. Fin-ray counts, myomere counts, and morphometric characters are very similar and of little diagnostic value. Based on these criteria, larvae of the cui-ui were identified in Pyramid Lake collections, and larvae and juveniles of the mountain and Tahoe suckers were identified in both lake and river collections.

On the geographic distribution and migration of I- and II-group eel larvae as studied during the 1979 Sargasso Sea Expedition

During the 1979 Sargasso Sea Expedition, 423 larvae ofAnguilla anguilla and 5 larvae ofA. rostrata were caught on three Atlantic transects and two cruises in the Sargasso Sea. Results of the identification of the larvae by myomere counts, and limits of the occurrence of I- and II-group larvae are presented. Four standard fishing depths are compared. A range shallower than 25 m was found to be the optimal fishing depth by night for both larval length groups. The geographic distribution of length group I was observed in central and eastern North Atlantic. Available data indicate a migration of these larvae in a north easterly direction. Length measurements of the II-group larvae taken from catches on the European continental slope during the same expedition support this assumption.

Larval stages of the lake chub, Couesius plumbeus

Three collections of Couesius plumbeus eggs were laboratory reared. Larvae were described with emphasis on external morphology. They were characterized by (1) 25 to 30 preanal myomeres, (2) a diagonal row of melanophores across the surface of the breast, and (3) a concentration of melanophores on the distal hypaxial portion of the caudal peduncle. Larval characteristics were compared with those of its breeding associate Rhinichthys cataractae and other sympatic cyprinids which have similarly high preanal myomere counts.

Egg and Larva Development of Brook Silversides from the Peace River, Florida

Abstract Brook silverside (Labidesthes sicculus) eggs, larvae, and juveniles were collected with a plankton net from the Peace River, Florida. Eggs had two or three attachment filaments (mode = 2) and a mean diameter of 1.2 mm. Oil globules were present in the yolk, and decreased from a mean of 22 after fertilization to one by the late embryo stage. Recently hatched protolarvae ranged from 4.7 to 5.6 mm total length and had six to seven and 28 to 31 postanal myomeres. The ratio of preanal length to total length increased as the anus migrated posteriorly during the metalarval phase; preanal myomere counts increased while postanal counts decreased. Pectoral anlages were present at hatching. By 8.0 mm, the base of the second dorsal and anal fins began to develop, and fin ray anlages were present in the caudal fin. Pelvic fin anlages appeared by 10.3 mm and all median fin rays were visible by 11.3 mm. The first dorsal fin developed between 11.3 and 15.5 mm. Metalarvae transformed into juveniles between 15.5 a...

Larval Development of Creek Chub and Fallfish from Two Susquehanna River Tributaries

Abstract Eggs of the creek chub (Semotilus atromaculatus) hatched 6 days after fertilization at a mean temperature of 18.3° C. Total length (TL) of newly hatched larvae ranged from 6.0 to 6.2 mm (average, 6.1 mm) and standard length from 5.8 to 6.0 mm (average, 5.9 mm). The newly hatched larvae were unpigmented, had pectoral fin buds, straight urostyles, and incomplete mouths. Transformation to the postlarval phase occurred by 9.2 mm TL and to the late postlarval phase by 14.2 mm TL. Eggs of the fallfish (Semotilus corporalis) were collected from a nest and the exact time of fertilization was not known. The eggs hatched about 24 h after collection. Total length of newly hatched larvae ranged from 6.8 to 7.5 mm (average, 7.1 mm) and standard length from 6.6 to 73 mm (average, 6.9 mm). The newly hatched larvae were unpigmented, had pectoral fin buds, straight urostyles, and incomplete mouths. Transformation to the postlarval phase occurred by 9.7 mm TL and to the late postlarval phase by 14.8 mm TL. Characteristics useful in distinguishing between creek chub and fallfish are prolarval size, preanal myomere counts, and lateral pigmentation patterns.

Ovigerous Leptocephali of the Nettastomatid Eel Genus Facciolella

Larvae of Facciolella have a slender body, elongate snout and olfactory organ, short straight gut and inconspicuous pigmentation. F. physonema occurs in the east Atlantic and F. gilberti in the east Pacific. Leptocephalus saurencheloides (Red Sea) is referred to Facciolella. Larval studies indicate a further species in the west Pacific, distinguished by its very high myomere count. Ova develop at the larval stage in F. physonema and in the west Pacific species. Each ovary contains about 2,000 ova of 0.045 mm mean diameter at the onset of metamorphosis. The sexually advanced condition of Facciolella leptocephali suggests that postmetamorphic life may be transient, accounting for the west Pacific species and F. saurencheloides being unknown as adults.

Identification of Golden Shiner, Notemigonus crysoleucas, Spotfin Shiner, Notropis spilopterus, and Fathead Minnow, Pimephales promelas, Larvae

The various proportional length measurements and myomere counts for each larval phase of the cyprinid fishes golden shiner, Notemigonus crysoleucas, spotfin shiner, Notropis spilopterus, and fathead minnow, Pimephales promelas, are generally quite similar and typical of the family. Mean snout to vent lengths for protolarvae and mesolarvae ranged from 58 to 60% of total length and decreased to 54 to 59% for metalarvae. Mean total myomere counts for all phases overlapped among the species and ranged from 34 to 37.Identification of protolarvae and mesolarvae depends largely on melanophore distribution and patterns, while fin ray counts and position are applicable to metalarvae. Later protolarvae and mesolarvae of Notemigonus crysoleucas exhibit a distinctive midventral line of pigment anterior to the vent, while metalarvae are readily distinguished by an anal ray count of over 10 and pelvic fins well anterior to the dorsal fin origin. The later protolarvae, mesolarvae, and metalarvae of Notropis spilopterus are distinguished by a lack of melanophores on the ventral surface of the gill covers.These and other distinguishing features discussed are not necessarily unique to the cyprmids studied. Unless potentially similar species (undescribed or inadequately described) in a study area can be eliminated, identifications based on these characters should be considered tentative. Key words: Notemigonus crysoleucas, Notropis spilopterus, Pimephales promelas, Cyprinidae, fish, larvae, development, identification, taxonomy

Larval Development of Spotted Sucker (Minytrema melanops)

Abstract Larval stages of spotted sucker, Minytrema melanops, were described using diagnostic characters. Suitable criteria for the identification of larval spotted sucker are fin ray counts, myomere counts, and pigmentation. Eggs reared in the laboratory at 16.1–20.0 C hatched between 108 and 156 h after fertilization. Newly hatched larvae averaged 6.0 mm in total length. The prolarval phase was complete 8 days after hatching at an average size of 10.5 mm. The juvenile phase was reached between 7 and 9 weeks at lengths of 20 to 23 mm. Five- to 6-day-old larvae, averaging 10.0-mm total length, initiated vertical movements in the culture tanks and, within a few hours, became totally free-swimming; these movements were associated with the air bladder beginning to fill. Larvae 7 to 8 days old formed a compact, integrated school when exposed to direct light but dispersed in a darkened vat. Postlarvae 15.0-mm total length and smaller fed at the surface and in the midregion of the culture vats. Postlarvae great...