Gill Raker Counts Research Articles

Anthropogenic hybridization between endangered migratory and commercially harvested stationary whitefish taxa (Coregonus spp.).

Natural hybridization plays a key role in the process of speciation. However, anthropogenic (human induced) hybridization of historically isolated taxa raises conservation issues. Due to weak barriers to gene flow and the presence of endangered taxa, the whitefish species complex is an excellent study system to investigate the consequences of hybridization in conservation. We focused on three naturally reproductively isolated whitefish taxa in Germany: the endangered, anadromous North Sea houting (NSH) and Baltic houting (BH), which were reintroduced after local extinction, and the commercially stocked European whitefish (EW). To evaluate the genetic integrity of each taxon, source and reintroduced populations of NSH and BH, and EW populations were characterized based on two mitochondrial and 17 microsatellite loci. Additionally, we investigated gill raker counts as an adaptive phenotypic trait. Even though clear genetic and phenotypic differentiation confirmed the houtings as separate evolutionarily significant units, admixture analyses revealed an extensive hybrid zone. Hybridizations were introgressive, positively correlated with genetic diversity, and were reflected in the gill raker counts. The BH distribution range showed higher heterogeneity and stronger admixture than the NSH range. Erroneous stocking with non-native genotypes best explained these patterns, which pose challenges for the conservation of the endangered NSH and BH.

Growth-related morphology of “Kunimasu” (Oncorhynchus kawamurae: family Salmonidae) from Lake Saiko, Yamanashi Prefecture, Japan

Biological characteristics of “Kunimasu” (Oncorhynchus kawamurae), poorly known even before the species was prematurely believed extinct, have now become apparent following the examination of 59 specimens from Lake Saiko, Yamanashi Prefecture, Japan and comparison with 58 examples of “Himemasu” (kokanee of Oncorhynchus nerka in Japan), also from Lake Saiko. Significant (p < 0.01) differences between Kunimasu and Himemasu from Lake Saiko occurred in counts of anal-fin rays, pectoral-fin rays, gill rakers (no overlap found) and pyloric caeca. Secondary sexual characters related to maturity level were also found in Kunimasu, the body being more compressed in pre-spawning and spawning males and females than in immature and maturing individuals. Furthermore, maturing male Kunimasu and Himemasu also differed in body shape. Body coloration of Kunimasu also differed according to level of maturity, the nuptial coloration in both sexes being olive-green when alive and black when fresh. Dark dots, found in ca. 40 % of Kunimasu individuals examined, were less distinct than in Himemasu. The spawning season of Kunimasu extended through winter and early spring in Lake Saiko, with spawning males and females remaining near the bottom, compared with non-spawning individuals which occupied the upper and middle profundal zones in the daytime.

Validation of Alburnus timarensis from the Lake Van basin, eastern Anatolia (Teleostei: Cyprinidae)

The Lake Van basin located in eastern Anatolia is inhabited by two species of Alburnus: Alburnus tarichi is a migratory species foraging in the lake and spawning in all tributaries, while A. timarensis is resident in streams and is known only from one tributary of the lake, the Karasu. It could be shown that A. timarensis is a valid species, which is rediagnosed here. Both species are syntopic during the spawning season, but are well distinguished by size, gill raker and lateral line scale counts.

Coexistence and origin of trophic ecotypes of pygmy whitefish,Prosopium coulterii, in a south‐westernAlaskan lake

Ecologically, morphologically and genetically distinct populations within single taxa often coexist in postglacial lakes and have provided important model systems with which to investigate ecological and evolutionary processes such as niche partitioning and ecological speciation. Within the Salmonidae, these species complexes have been well studied, particularly within the Coregonus clupeaformis-C. laveratus (lake and European whitefish, respectively) group, but the phenomenon has been less well documented in the other whitefish genera, Prosopium and Stenodus. Here, we examined the morphology, feeding biology and genetic structure of three putative forms of the pygmy whitefish, Prosopium coulterii (Eigenmann & Eigenmann, 1892), first reported from Chignik Lake, south-western Alaska, over 40 years ago. Field collections and morphological analyses resolved a shallow water (< 5 m depth) low gill raker count form (< 15 first arch gill rakers), a deepwater (> 30 m), low gill raker form and a deepwater, high gill raker count (> 15 gill rakers) form. The two low gill raker count forms fed almost exclusively on benthic invertebrates (mostly chironomids), while the deepwater, high gill raker count form fed almost exclusively on zooplankton; differences in diet were also reflected in differences both in δ(13) C and δ(15) N stable isotopes. All three forms were characterized by the same major mitochondrial DNA clade that has been associated with persistence in, and postglacial dispersal from, a Beringian glacial refugium. Analysis of variation at nine microsatellite DNA loci indicated low, but significant differentiation among forms, especially between the two low gill raker count forms and the high gill raker count form. The extent of differentiation along phenotypic (considerable) and genetic (subtle) axes among the Chignik Lake forms is similar to that found among distinct taxa of Prosopium found in pre-glacial Bear Lake (Utah-Idaho, USA) which is probably at least ten times older than Chignik Lake. Our analyses illustrate the potential for the postglacial differentiation in traits subject to divergent natural selection across variable environments.

Morphological variations in bluegill, Lepomis macrochirus, with particular emphasis on growth-related changes

Morphological variations in bluegill, Lepomis macrochirus, including growth-related changes, sexual dimorphism and morphological differences between populations in different habitats, were examined in samples from three reservoirs in Kagawa, Japan. Body measurements demonstrated frequent growth-related proportional changes, particularly in body depth, body width, caudal peduncle length and head length, which all showed relative increases, whereas first dorsal fin length, caudal fin length and orbital diameter became relatively shorter. Body weight increased relatively with growth, with relative growth coefficients of 3.339–3.454 for regressions between total length and body weight. Such body weight increases were likely due to the relative increases in body depth and width, and caudal peduncle depth. Although counts of fin spines, fin rays and gill rakers did not change with growth, those of scales tended to increase. Males were significantly larger than females in body depth, caudal peduncle length, head length and body weight. Sexual dimorphism was also apparent in body coloration during the breeding season. In addition, a number of morphological differences were observed between individuals from different habitats.

A new species of Upeneus (Perciformes: Mullidae) from southern Japan

A new species of goatfish, Upeneus itoui, is described on the basis of 67 specimens collected from southern Japan at depths of less than 40 m. Upeneus itoui is most similar to the western Indian Ocean species, U. pori. The caudal-fin color pattern in fresh and preserved specimens of the two species is identical. However, U. itoui differs from U. pori in having less head and body depths, wider barbels, and a lower count of gill rakers.

Two new sympatric Sarotherodon species (Pisces: Cichlidae) endemic to Lake Ejagham, Cameroon, west-central Africa, with comments on the Sarotherodon galilaeus species complex

Morphometric differentiation among 25 populations of the widespread Sarotherodon galilaeus species complex is investigated, and two new species are described from Lake Ejagham, Cameroon in west-central Africa. Sarotherodon lamprechti sp. nov. is characterized by a prognathous lower jaw, scales over the pectoral fin-base restricted at maximum to the basal third, and an elongate ventral keel on the lower pharyngeal jaw. Sarotherodon knauerae sp. nov. is characterized by the possession of an inflated second pharyngobranchial element of the upper pharyngeal jaw, and small size at maturation. It is further differentiated from its sympatric congener in having a shorter anal fin (12.0–14.6 % SL vs. 14.1–15.7 % SL), larger eyes (24.0–31.2 % HL vs. 20.4– 29.2 % HL), higher total gill raker count (24–30 vs. 20–25), and a terminal mouth. Molecular evidence for a sister group relationship for these two sympatric species is corroborated by the shared possession of a reduced number of teeth on the second pharyngobranchial element of the upper pharyngeal jaw.

A highly permeable species boundary between two anadromous fishes

Meristic identification, mitochondrial DNA and a suite of microsatellite markers were employed to estimate the incidence of hybridization in wild populations of anadromous Allis shad Alosa alosa and twaite shad Alosa fallax in southern Irish riverine and estuarine waters. It was shown that 16% of the fishes examined were misclassified using meristic count of gill rakers. Next, a significant proportion of fishes that were robustly assigned to a species using nuclear markers were shown to possess the mtDNA of the other. The genomes of A. alosa and A. fallax in Ireland are extensively introgressed, which suggests a complex history of hybridization between these species, which can only partially be explained by recent man-made habitat changes.

Phenotype‐environment correlations in a putative whitefish adaptive radiation

1. The adaptive radiation of fishes into benthic (littoral) and pelagic (lentic) morphs in post-glacial lakes has become an important model system for speciation. Although these systems are well studied, there is little evidence of the existence of morphs that have diverged to utilize resources in the remaining principal lake habitat, the profundal zone. 2. Here, we tested phenotype-environment correlations of three whitefish (Coregonus lavaretus) morphs that have radiated into littoral, pelagic and profundal niches in northern Scandinavian lakes. We hypothesized that morphs in such trimorphic systems would have a morphology adapted to one of the principal lake habitats (littoral, pelagic or profundal niches). Most whitefish populations in the study area are formed by a single (monomorphic) whitefish morph, and we further hypothesized that these populations should display intermediate morphotypes and niche utilization. We used a combination of traditional (stomach content, habitat use, gill raker counts) and more recently developed (stable isotopes, geometric morphometrics) techniques to evaluate phenotype-environment correlations in two lakes with trimorphic and two lakes with monomorphic whitefish. 3. Distinct phenotype-environment correlations were evident for each principal niche in whitefish morphs inhabiting trimorphic lakes. Monomorphic whitefish exploited multiple habitats, had intermediate morphology, displayed increased variance in gillraker-counts, and relied significantly on zooplankton, most likely due to relaxed resource competition. 4. We suggest that the ecological processes acting in the trimorphic lakes are similar to each other, and are driving the adaptive evolution of whitefish morphs, possibly leading to the formation of new species.

Patterns of morphological changes and hybridization between sympatric whitefish morphs (Coregonus spp.) in a Swiss lake: a role for eutrophication?

Whitefish, genus Coregonus, show exceptional levels of phenotypic diversity with sympatric morphs occurring in numerous postglacial lakes in the northern hemisphere. Here, we studied the effects of human-induced eutrophication on sympatric whitefish morphs in the Swiss lake, Lake Thun. In particular, we addressed the questions whether eutrophication (i) induced hybridization between two ecologically divergent summer-spawning morphs through a loss of environmental heterogeneity, and (ii) induced rapid adaptive morphological changes through changes in the food web structure. Genetic analysis based on 11 microsatellite loci of 282 spawners revealed that the pelagic and the benthic morph represent highly distinct gene pools occurring at different relative proportions on all seven known spawning sites. Gill raker counts, a highly heritable trait, showed nearly discrete distributions for the two morphs. Multilocus genotypes characteristic of the pelagic morph had more gill rakers than genotypes characteristic of benthic morph. Using Bayesian methods, we found indications of recent but limited introgressive hybridization. Comparisons with historical gill raker data yielded median evolutionary rates of 0.24 haldanes and median selection intensities of 0.27 for this trait in both morphs for 1948-2004 suggesting rapid evolution through directional selection at this trait. However, phenotypic plasticity as an alternative explanation for this phenotypic change cannot be discarded. We hypothesize that both the temporal shifts in mean gill raker counts and the recent hybridization reflect responses to changes in the trophic state of the lake induced by pollution in the 1960s, which created novel selection pressures with respect to feeding niches and spawning site preferences.

A new species of ladyfish, of the genus Elops (Elopiformes: Elopidae), from the western Atlantic Ocean

v This paper describes Elops smithi, n. sp., and designates a lectotype for E. saurus. These two species can be separated from the five other species of Elops by a combination of vertebrae and gillraker counts. Morphologically, they can be distinguished from each other only by myomere (larvae) or vertebrae (adults) counts. Elops smithi has 73–80 centra (total number of vertebrae), usually with 75–78 centra; E. saurus has 79–87 centra, usually with 81–85 centra. No other morphological character is known to separate E. smithi and E. saurus, but the sequence divergence in mtDNA cytochrome b (d = 0.023–0.029) between E. smithi and E. saurus is similar to or greater than that measured between recognized species of Elops in different ocean basins. Both species occur in the western Atlantic Ocean, principally allopatrically but with areas of sympatry, probably via larval dispersal of E. smithi by oceanographic currents.

Effect of parasitic isopods in the marine fish Carangids malabaricus off Parangipettai coastal waters

The effect of parasitic isopods on the fish Carangids malabaricus was studied. The reduction in gill raker count and gill surface area was observed as a function of infestation. The maximum reduction in respiratory surface area was observed in the first gill arch and the minimum in the third gill arch. Infested fish had extremely pale gills, indicating severe anaemia. Gill rakers were seriously lost, apical edges damaged and out off gill lamellae heavily destroyed. Some secondary gill lamellae were fused or thickened. Between the gill lamellae, callus-like thickening was observed. The histopathological symptoms owing to isopod parasites (Joryma tartoor) were categorised as gross lesions and histopathological anomalies noticed in the present study.

The Alabama Bass, Micropterus henshalli (Teleostei: Centrarchidae), from the Mobile River basin

The Alabama Bass, Micropterus henshalli, was diagnosed as a subspecies of Micropterus punctulatus from the Mobile River basin, Alabama, Georgia, and Mississippi, USA, by Hubbs and Bailey (1940). The species has been introduced in the Chattahoochee River, as has the Spotted Bass, Micropterus punctulatus. Micropterus henshalli differs from M. punctulatus, with which it has been aligned, by having higher scales counts, a narrower head, smaller scale width, higher gill raker count, and a smaller tooth patch. It also has a narrower and more elongate body shape than does M. punctulatus. The Alabama Bass is relatively common in streams and rivers throughout the Mobile River basin.

Review of the waspfish genus Liocranium (Scorpaeniformes: Tetrarogidae), with restoration of L. pleurostigma (Weber)

A taxonomic review of the waspfish genus Liocranium Ogilby, 1903 (Tetrarogidae) resulted in two species of the genus being regarded as valid: L. praepositum Ogilby, 1903 (type species of the genus) and L. pleurostigma (Weber, 1913) (previously regarded as a junior synonym of L. praepositum). Liocranium pleurostigma is distinguished from L. praepositum by colour pattern, gill-raker counts and several morphometrics, including upper-jaw length, depth of the posterior margin of the maxilla, length of the longest anal-fin soft ray, and position of the spine tip of the depressed pelvic fin. Lectotypes of the two nominal species are herein designated. Liocranium pleurostigma is distributed off the northwestern coast of Australia (east to Torres Strait), New Guinea and the Philippines, whereas L. praepositum occurs off the northeastern coast of Australia (north to about Hinchinbrook Island). Comments on the biogeography of Liocranium are also provided.

Threatened fishes of the world: Anabarilius alburnops (Regan, 1914), a member of the family Cyprinidae (Pisces: Teleostei)

Common name: Silvery white fish (English). Figure from Chu and Chen (1989). Local name: Xiao Bai Yu (Chinese). Conservation status: Endangered – China Red Data Book of Endangered Animals, Pisces (Yue and Chen 1998); Anabarilius alburnops is one of the critically endangered fishes in Lake Dianchi (24°28′– 25°28′ N, 102°30′–103°00′ E, 1,886 m above sea level), Yunnan, China. Identification: Lateral line curved markedly downward above pectoral fin; lateral line scales 76–81. Gill raker count is 43–50 (Regan 1914; Chu and Chen 1989; Chen 1998). Distribution: Endemic to Lake Dianchi and probably found in Songhuaba reservoir in Yunnan Province. Abundance: This species was very common in Lake Dianchi prior to the mid-twentieth century. The population started to decline throughout the lake during the 1970s (Yue and Chen 1998), and is now very rare in the lake. No specimens had been collected from the lake until three individuals were observed in DaYu village (24°50′ 36.06′′ N, 102°45′59.86′′ E), Chenggong County in August 1999. Habitat and ecology: Anabarilius alburnops lives in the middle and upper layers of the water column and feeds on various food items; mainly aquatic insects, plankton and plants (Chu and Chen 1989; Chen 1998; Yue and Chen 1998). Reproduction: It becomes sexually mature after one winter; eggs are adhesive (Yue and Chen 1998). Threats: Its loss from the lake is thought to be due to introduced fish species, deterioration of water quality, loss of macrophytes (in part due to grass carp), and over-fishing; as well as loss of breeding sites due to siltation and blocked access. Conservation recommendations: Destructive fishing practices should be strictly prohibited (Yue and Chen 1998). The conservation status of A. alburnops can be improved through effective habitat protection, increased public awareness, and long-term monitoring and surveys. Environ Biol Fish (2008) 83:505–506 DOI 10.1007/s10641-008-9373-3

Aspects of anadromous Allis shad (Alosa alosa Linnaeus) and Twaite shad (Alosa fallax Lacépède) biology in four Irish Special Areas of Conservation (SACs): status, spawning indications and implications for conservation designation

Four Special Areas of Conservation (SACs) have been designated in the Republic of Ireland for Twaite shad, Alosa fallax (Lacepede), based on recent historical information on spawning activity—the estuarine reaches of the Rivers Munster Blackwater, Suir, Barrow–Nore and Slaney. The spawning status of some of these populations is considered to have declined substantially in recent years, and no known spawning areas of Allis shad, Alosa alosa (L.), are known for Ireland. Data are presented confirming the presence of both Allis shad and Twaite shad in all four SACs. The majority of the material has come as by-catch from estuarine commercial salmon netsmen. Angling is the principal source of material from the R. Barrow. Examination of scale and gonad material of Allis shad indicates some degree of readiness for spawning as well as spawning having taken place. Gonadosomatic index (GSI) data from the R. Barrow for Twaite shad in the May spawning period (2000–2002) had mean GSIs of 13.7–15% with maxima in the range of 21–28%. GSI values of 18% and 22% have been recorded in the July period for individual Allis shad from the upper estuaries of the R. Slaney and R. Suir, respectively, with both fish displaying gonad maturity stage V or VI (after Pina, 2000). Low GSI values have been recorded from other Allis shad in the June–July period displaying gonad condition varying from stage III (immature) to stage VIII (spent). These findings point to a possibility that Allis shad do engage in spawning activity, whether mono-specifically or with Twaite shad. The possibility of the latter is supported by gill raker count data presented. These show clearly defined value ranges for Twaite and for Allis as well as a series of fish with intermediate counts. The apparently low population levels of Twaite shad within the SACs identify a need to examine what measures might be undertaken to ensure the favourable conservation status of this species.

Southernmost occurrence of the slender tuna, Allothunnus fallai, off Tierra del Fuego, South Atlantic Ocean

The slender tuna, Allothunnus fallai Serventy 1948, is an epipelagic scombrid with a circumglobal distribution in the Southern Ocean from about 20–50 S (Warashina and Hisada 1972; Collette and Nauen 1983), south to 54 S in the South Pacific (Yatsu 1995), with three exceptions from the North Pacific (Schaefer and Childers 1999). Recently, an adult male, 784-mm fork length (Fig. 1) was taken further south in the South Atlantic, at 53 250S, 64 230W off Tierra del Fuego, Argentina. It was caught while trawling at 167 m on March 12, 2007 by the fishing vessel Tai An. The surface water temperature was 8 C and the salinity 33.59 parts per thousand (ppt). The specimen has been deposited in the fish collection of the Instituto Nacional de Investigacion y Desarrollo Pesquero under number INIDEP 801. Measurements and counts (Table 1) follow the methods of Collette and Chao (1975) and Schaefer and Childers (1999). External characters agree with descriptions given by previous authors (Serventy 1948; Collette and Chao 1975; Collette and Nauen 1983; Schaefer and Childers 1999). The elongate and rounded shape of the body and the lack of body markings (Fig. 1) are characteristic of this species. Fin-ray and especially, gill-raker counts of 74 confirm the identification. Slender tuna make seasonal migrations from subantarctic and transitional waters to subtropical waters, coupled to seasonal geographic shifts in biomass of epipelagic subantarctic zooplankton (Yatsu 1995). Slender tuna appear to spawn in subtropical waters and in the Peru Current, from approximately 20–30 S, October–December at sea-surface temperatures of 17–25 C (Watanabe et al. 1966; Yatsu 1995). Juveniles are principally encountered between 20 and 35 S at surface temperatures ranging from 19 to 24 C. With increasing size, they gradually move into higher latitudes where water temperatures are lower. Distributions of three species of scombrids are concentrated in the Southern Ocean (Warashina and Hisada 1972; Collette and Nauen 1983; Collette et al. 2001): A. fallai; the butterfly mackerel, Gasterochisma melampus Richardson 1845; and the southern bluefin tuna, Thunnus maccoyii (Castelnau 1872). All species of the tribe Thunnini, except for Allothunnus Serventy 1948, have counter-current heat exchanger systems that allow them to retain body heat generated by muscular contractions thus keeping their bodies warmer than the surrounding sea temperature (Graham and Dickson 2000). Gasterochisma Richardson, 1845 has a layer of fat under the scales and has a brain heater that may be involved in keeping them warm. Recently Sepulveda et al. (2007) showed that Allothunnus also has a heater, extraocular muscles that differ from other tunas and serve as a heater organ that can raise cranial temperatures about 4.8 C above ambient sea temperature. Also, the small central vascular plexus of Allothunnus may be capable of conserving metabolic heat generated by continuous swimming to elevate red muscle temperatures (Graham and Dickson 2000) but body temperatures of Allothunnus are as yet unreported. B. B. Collette (&) National Marine Fisheries Systematics Laboratory, Smithsonian Institution, National Museum of Natural History, P.O. Box 37012, Washington, DC 20013-7012, USA e-mail: collettb@si.edu

The Oarfish,Regalecus glesne(Teleostei: Regalecidae), in the Western Caribbean

In two consecutive years, 2005 and 2006, specimens of Regalecus have been observed or collected on the reef at the southern end of Cozumel Island, Mexican Caribbean, between February and May. A single specimen has been preserved. Although a large part of the body is missing, the fish was identified as Regalecus glesne Ascanius, 1772, on the basis of the total gill-raker count on the first arch (35), the number of prolonged, cephalic dorsal-fin rays (9) and the relative length of the prolonged pelvic- fin ray (more than twice the head length). The mutilation of the specimen is probably not the result of autotomy, because the exposed vertebra is broken and the gut is sectioned; the shape of the cut suggests that a shark bit off the rear half of the body. While R. glesne has been recorded several times in Florida, Bermuda, and even the northern coast of Cuba, these are the first documented records of Regalecus in the Caribbean Sea proper. The strong seasonality of the records of R. glesne in the region (always between February and July) suggests that the fish may come closer to the coast attracted by seasonal upwelling.

Larval development in the lutjanid subfamily Lutjaninae (Pisces): the genus Macolor

Larval development of the Indo-west Pacific lutjanine lutjanid Macolor niger is described based on pelagic larvae (4.8-10 mm) from western Pacific plankton hauls, settlement-stage larvae (17-19 mm) from Great Barrier Reef light-trap catches and Solomon Island reef-crest net catches, and settled juveniles (26-32 mm) from the western Pacific. The larvae possess all the characteristics of lutjanids (24 myomeres; elongate dorsal spine 2 and pelvic spine; pelvic ray 1 longer than spine; postcleithral spine; extensive, large, smooth head spines; and fin-ray counts of DX,14-15, AIII,10-11, P 1 17-18), and corroborate the inclusion of Macolor in the Lutjanidae. The larvae have long, weakly serrate, robust fin spines, with the serrations largely disappearing by settlement at 17-19 mm. Unique meristic values (in particular fin-ray and gill-raker counts) and distinctive colour pattern at settlement confirm the identification. Settled juvenile M. macularis (17-20 mm) from the western Pacific are similar to M. niger, but are slightly deeper bodied, with much longer elements in the pelvic fin and spiny dorsal fin. Distinctive meristics and pigment patterns separate the two species.

Astyanax cocibolca, a new characid (Pisces: Ostariophysi) from Lake Nicaragua, Central America

Astyanax cocibolca, a small filter-feeding species is a new characid species endemic to Lake Nicaragua. It is distinguished from the syntopic Astyanax aeneus by its high gill raker count, slender body, upturned snout, long maxillary bones, conical outer premaxillary teeth, lower number of scales above lateral line, more intense black lateral band, smaller size, and trophic niche partitioning. At present the new species utilizes the open-water habitat at least as a nursery where young can feed on the rich plankton population. Adults feed on copepoda, cladocera, fruits, seeds and algae. The bulk of the adult population presumably resides inshore.