Incipient speciation in allopatric Etheostoma rupestre (Percidae: Etheostomatinae) lineages, with the description of three new subspecies.

In recent years, new species descriptions for the North American darters have proliferated. Most species concepts accepted by contemporary ichthyologists require that a valid species be both monophyletic and diagnoseable, yet many lineages exhibit modal or range differences in morphological characteristics without individuals being diagnosable. Such scenarios present difficulties with regards to proper taxonomic recognition of divergent lineages and often prohibit appropriate conservation action. Following the example of recent authors, we provide meristic, geometric morphometric, and pigmentation data to support the recognition of three subspecies of Etheostoma rupestre, a species endemic to the Mobile Basin. These morphological data cohere with previous genetic work for E. rupestre. The nominate subspecies Etheostoma rupetsre rupestre (Tsais Rock Darter) is endemic to the Tombigbee River and Black Warrior River watersheds in Alabama and Mississippi and is characterized by having lower numbers of lateral blotches, lower range and mean of lateral line scales, lower modal number of scales above the lateral line, and lower degrees of nape squamation than other subspecies. Etheostoma rupestre piersoni (Shamrock Darter), ssp. nov., is endemic to the Cahaba and Alabama River Watersheds in Alabama and is characterized by intermediate counts of lateral blotches and higher scale counts and nape squamation than E. r. rupestre. Etheostoma rupestre uphapeense (Jade Darter), ssp. nov., is restricted to several small, disjunct populations in the Coosa and Tallapoosa watersheds in Alabama, Georgia, and Tennessee. Etheostoma r. uphapeense is characterized by having a higher mean number of lateral blotches than both other subspecies and higher scale counts than E. r. rupestre. While E. r. rupestre and E. r. piersoni are widespread and abundant within their respective ranges, E. r. uphapeense has a disjunct range and is often uncommon where it occurs. Etheostoma r. uphapeense should be monitored where it occurs to discern population trends.

Proteomic profile and morphological characteristics of skeletal muscle from the fast- and slow-growing yellow perch (Perca flavescens).

The objective of the present study was to compare skeletal muscle proteomic profiles, histochemical characteristics, and expression levels of myogenic regulatory factors (MRFs) between fast- versus slow-growing yellow perch Perca flavescens and identify the proteins/peptides that might play a crucial role in the muscle growth dynamic. Yellow perch were nursed in ponds for 6 weeks from larval stage and cultured in two meter diameter tanks thereafter. The fingerlings were graded to select the top 10% and bottom 10% fish which represented fast- and slow-growing groups (31 yellow perch per each group). Our statistical analyses showed 18 proteins that had different staining intensities between fast- and slow-growing yellow perch. From those proteins 10 showed higher expression in slow-growers, and 8 demonstrated higher expression in fast-growers. Fast-growing yellow perch with a greater body weight was influenced by both the muscle fiber hypertrophy and mosaic hyperplasia compared to slow-growing fish. These hyperplastic and hypertrophic growth in fast-grower were associated with not only metabolic enzymes, including creatine kinase, glycogen phosphorylase, and aldolase, but also myoD and myogenin as MRFs. Overall, the results of the present study contribute to the identification of different expression patterns of gene products in fast- and slow-growing fish associated with their muscle growth.

Muscle cellularity, growth performance and growth-related gene expression of juvenile climbing perch Anabas testudineus in response to different eggs incubation temperature.

Although indigenous climbing perch (Anabas testudineusis) is a highly valuable species, slow growth pattern during the culture period impeding its commercial success in aquaculture. In many fish species, it has been demonstrated that incubation temperature of eggs influenced the muscle development and growth rates, which persisted throughout the subsequent larval and juvenile phases. Therefore, this study aimed to investigate whether different incubation temperature of eggs prior to hatching can stimulate the muscle development, growth, and growth-related gene expression of the slow-growing indigenous species of climbing perch. The fertilized eggs of A. testudineus from an artificial breeding program were incubated under control temperature of 24 °C (IT24), 26 °C (IT26), 28 °C (IT28), and 30 °C (IT30) in 10L glass aquaria with four replicated units for each temperature treatment. After hatching, the larvae from each incubated temperature were separately reared at ambient temperature for 10 days in aquarium, 20 days in hapas, and the next 42 days in cages, totaling 72 days post-hatching (dph). The hatching rates were found significantly (P < 0.05) higher in IT28 compared to the other incubation temperature treatments. After 72 dph, the growth performances (%length gained, %weight gained and SGR) were found to be significantly highest (P < 0.05) in the IT28, followed by the treatments IT30, IT26, and IT24, respectively. Survival rate (73 ± 1.257%) was also found to be highest in the same treatment. The rate of new muscle fiber formation was identified to be significantly highest (P < 0.05) in IT28 followed by the IT26, IT30 and IT24, respectively. The relative mRNA expression level of GHRH, IGF1, IGF2 and PRL was also significantly highest in the IT28 (P < 0.05) compared to other treatments. Results from the present study clearly suggested that 28 °C is the optimum eggs incubation temperature of the native strain of A. testudineus for its highest growth performances in captive breeding condition.

Fish size effect on sagittal otolith outer shape variability in round goby Neogobius melanostomus (Pallas 1814).

Round goby Neogobius melanostomus (Pallas 1814) has become a significant component in the diet of piscivorous fish from the Pomeranian Bay (Bornholm Basin, Baltic Sea). Proper identification of fish species in the diet of predators is significant in biological studies of fish and other aquatic animal species, and, with regard to N. melanostomus, it is important to the knowledge of trophic web structures in areas this species has invaded. A total of 142 individuals of N. melanostomus, measuring 16-174 mm standard length, were examined. Seventy-two fishes were caught during monitoring surveys in fishing grounds, whereas 70 were found in the stomachs of European perch Perca fluviatilis, pike-perch Sander lucioperca and Baltic cod Gadus morhua. The objective of the present study was to analyse the sagittal otoliths to identify variations in outer shape with increases in fish length; expand and correct descriptions of the sagitta, lapillus and asteriscus otoliths; and evaluate the relationships among otolith dimensions and fish standard length. The otoliths were described morphologically. The analysis of the outer shape of sagittal otoliths using Fourier analysis and multivariate statistics exhibited great phenotypic variability that was associated with fish length, including within pairs in individuals and/or among individuals in length classes. In addition, the asterisci and lapilli of N. melanostomus from selected specimens, which were described for the first time with regard to fish length, were found to be less variable compared to sagittal otoliths. This study presents the first analysis of intrapopulation phenotypic plasticity of N. melanostomus sagittal otolith morphology as it is linked to fish size.

Differences in morphological growth trajectories between greenside darter Etheostoma blennioides populations from two distinct drainages.

The greenside darter Etheostoma blennioides is a small-bodied benthic stream fish that occurs in multiple drainages of the eastern USA. Previous studies have revealed some morphological differentiations among greensides from isolated drainage systems but growth relationships among functional morphological characteristics have not been examined within and between populations. Specifically, we tested for differences in functional morphology and allometric distinctions in morphological growth trajectories between greenside populations from two drainages, the Osage River and White River. Morphological differences between individuals of the two drainages included more dorso-ventrally compressed bodies, longer snouts and larger jaw features in White River darters. Furthermore, body depth, snout length and jaw width grow at significantly different trajectories in individuals of the two drainages. Individuals of the White River drainage (generally a higher gradient stream system) become comparatively more streamlined and develop proportionately larger feeding related traits during growth. These results suggest that individuals of both drainages share a similar morphology during early life but deviate during continued development and this may be partially due to environmentally induced plastic response. This study represents a novel approach for comparing morphological development among fish populations and presents environmental factors (e.g., stream gradient and elevation) that potentially influence functional characteristics.

Comparative transcriptome analysis reveals potential evolutionary differences in adaptation of temperature and body shape among four Percidae species.

Considering the divergent temperature habitats and morphological traits of four Percidae species: yellow perch (Perca flavescens), Eurasian perch (Perca fluviatilis), pike perch (Sander lucioperca), and ruffe (Gymnocephalus cernua), we stepped into the transcriptome level to discover genes and mechanisms that drive adaptation to different temperature environments and evolution in body shape. Based on 93,566 to 181,246 annotated unigenes of the four species, we identified 1,117 one-to-one orthologous genes and subsequently constructed the phylogenetic trees that are consistent with previous studies. Together with the tree, the ratios of nonsynonymous to synonymous substitutions presented decreased evolutionary rates from the D. rerio branch to the sub-branch clustered by P. flavescens and P. fluviatilis. The specific 93 fast-evolving genes and 57 positively selected genes in P. flavescens, compared with 22 shared fast-evolving genes among P. fluviatilis, G. cernua, and S. lucioperca, showed an intrinsic foundation that ensure its adaptation to the warmer Great Lakes and farther south, especially in functional terms like "Cul4-RING E3 ubiquitin ligase complex." Meanwhile, the specific 78 fast-evolving genes and 41 positively selected genes in S. lucioperca drew a clear picture of how it evolved to a large and elongated body with camera-type eyes and muscle strength so that it could occupy the highest position in the food web. Overall, our results uncover genetic basis that support evolutionary adaptation of temperature and body shape in four Percid species, and could furthermore assist studies on environmental adaptation in fishes.

Photoreceptors and eyes of pikeperch Sander lucioperca, pike Esox lucius, perch Perca fluviatilis and roach Rutilus rutilus from a clear and a brown lake.

The photoreceptors and eyes of four fish species commonly cohabiting Fennoscandian lakes with different light transmission properties were compared: pikeperch Sander lucioperca, pike Esox lucius, perch Perca fluviatilis and roach Rutilus rutilus. Each species was represented by individuals from a clear (greenish) and a humic (dark brown) lake in southern Finland: Lake Vesijärvi (LV; peak transmission around 570 nm) and Lake Tuusulanjärvi (LT; peak transmission around 630 nm). In the autumn, all species had almost purely A2-based visual pigments. Rod absorption spectra peaked at c.526 nm (S. lucioperca), c. 533 nm (E. lucius) and c. 540 nm (P. fluviatilis and R. rutilus), with no differences between the lakes. Esox lucius rods had remarkably long outer segments, 1.5-2.8-fold longer than those of the other species. All species possessed middle-wavelength-sensitive (MWS) and long-wavelength-sensitive (LWS) cone pigments in single, twin or double cones. Rutilus rutilus also had two types of short-wavelength sensitive (SWS) cones: UV-sensitive [SWS1] and blue-sensitive (SWS2) cones, although in the samples from LT no UV cones were found. No other within-species differences in photoreceptor cell complements, absorption spectra or morphologies were found between the lakes. However, E. lucius eyes had a significantly lower focal ratio in LT compared with LV, enhancing sensitivity at the expense of acuity in the dark-brown lake. Comparing species, S. lucioperca was estimated to have the highest visual sensitivity, at least two times higher than similar-sized E. lucius, thanks to the large relative size of the eye (pupil) and the presence of a reflecting tapetum behind the retina. High absolute sensitivity will give a competitive edge also in terms of short reaction times and long visual range.

Agonistic character displacement of genetically based male colour patterns across darters.

Agonistic character displacement (ACD) occurs when selection to avoid maladaptive interspecific aggression leads to the evolution of agonistic signals and/or associated behavioural biases in sympatry. Here, we test for a pattern consistent with ACD in male colour pattern in darters (Percidae: Etheostoma). Male colour pattern has been shown to function in male-male competition rather than female mating preferences in several darter species. Additionally, males bias their aggression towards conspecific over heterospecific males in sympatry but not in allopatry, consistent with divergent ACD in male behavioural biases. We use a common garden approach to show that differences in male colour pattern among four closely related darter species are genetically based. Additionally, we demonstrate that some aspects of male colour pattern exhibit enhanced differences in sympatric compared to allopatric populations of two darter species, consistent with ACD. However, other male colour traits are more similar between species in sympatry compared with allopatry, indicating that not all signal components are under strong divergent selection in sympatry. This study provides evidence that interspecific male-male aggressive interactions alone can promote elaborate male signal evolution both between and within species. We discuss the implications this has for male-driven ACD and cascade ACD.

Variation in flexural stiffness of the lepidotrichia within and among the soft fins of yellow perch under different preservation techniques.

Although the ray-finned fishes are named for their bony, segmented lepidotrichia (fin rays), we are only beginning to understand the morphological and functional diversity of this key vertebrate structure. Fin rays support the fin web, and their material properties help define the function of the entire fin. Many earlier studies of fin ray morphology and function have focused on isolated rays, or on rays from only one or two fins. At the same time, relatively little is known about how different preservation techniques affect the material properties of many vertebrate structures, including fin rays. Here, we use three-point bending tests to examine intra- and inter-fin variation in the flexural stiffness of fin rays from yellow perch, Perca flavescens. We sampled fin rays from individuals that were assigned to one of three preservation treatments: fresh, frozen, and preserved with formalin. The flexural stiffness of the fin rays varied within and among fins. Pelvic-fin rays were the stiffest, and pectoral fin rays the least stiff. The fin rays of the dorsal, anal, and caudal fins all had similar stiffness values, which were intermediate relative to those from the paired fins. The flexural stiffness of the fin rays was higher in rays that were at the leading edge of the fin. This variation in flexural stiffness was associated with variation in joint density and the relative length of the unsegmented proximal base of the fin rays. There was no significant difference in flexural stiffness between fresh and frozen specimens. In specimens preserved with formalin, there is a small but significant effect on stiffness in smaller fin rays.

Spawning-stock characteristics and migration of a lake-bound population of the endangered Macquarie perch Macquaria australasica.

The intrapopulation variability in the size and age structure of the spawning stock and migration of the threatened Macquarie perch Macquaria australasica in Lake Dartmouth was investigated between 2008 and 2016. Sampling centred on the core reproductive period (October-December) when mature fish migrate from the lake into riverine habitat to spawn. Spawning fish were predominantly large, spanning a broad age structure, with a high proportion of fish (25%) aged 15-30 years. The overall median size of spawning fish did not change for males or females during the 9 year study period. The size of the smaller mature male fish did change in some years suggesting a small proportion of male M. australasica matured at age 1+ and 2+. Acoustic telemetry employed over 3 years showed that M. australasica were most likely to be in the spawning reach from October to mid-December, migrated to this reach annually and moved large distances throughout the lake all year, with no evidence for any spatial structuring. Mature fish sometimes occupied the spawning reach for several months after the core reproductive period, which increased their vulnerability to recreational fishing. Males tagged in the lake were seldom recorded in the spawning reach, presumably because a high proportion had not yet entered the spawning stock despite their size suggesting maturity. Maintaining a broad age and size-structure of the spawning stock of long-lived iteroparous fish species is crucial for recruitment stability and population persistence. Overexploitation of the spawning stock has probably contributed to previous population declines in the lake as well as the collapse of other M. australasica populations in south-eastern Australia.

Chemicals released by predation increase the growth rate of yellow perch, Perca flavescens.

Water-soluble factors associated with walleye Sander vitreus predation on either yellow perch Perca flavescens or fathead minnows Pimephales promelas markedly increased the growth rate of P. flavescens. The findings suggest that P. flavescens possess an inducible growth-promoting mechanism regulated by water-born chemicals. It may be possible to increase the growth rate of farm-raised P. flavescens by manipulating this system.

Fossil climbing perch and associated plant megafossils indicate a warm and wet central Tibet during the late Oligocene.

Understanding the Tibetan Plateau's palaeogeography and palaeoenvironment is critical for reconstructing Asia's climatic history; however, aspects of the plateau's uplift history remain unclear. Here, we report a fossil biota that sheds new light on these issues. It comprises a fossil climbing perch (Anabantidae) and a diverse subtropical fossil flora from the Chattian (late Oligocene) of central Tibet. The fish, Eoanabas thibetana gen. et sp. nov., is inferred to be closely related to extant climbing perches from tropical lowlands in south Asia and sub-Saharan Africa. It has osteological correlates of a labyrinth organ, which in extant climbing perches gives them the ability to breathe air to survive warm, oxygen-poor stagnant waters or overland excursion under moist condition. This indicates that Eoanabas likewise lived in a warm and humid environment as suggested by the co-existing plant assemblage including palms and golden rain trees among others. As a palaeoaltimeter, this fossil biota suggests an elevation of ca. 1,000 m. These inferences conflict with conclusions of a high and dry Tibet claimed by some recent and influential palaeoaltimetry studies. Our discovery prompts critical re-evaluation of prevailing uplift models of the plateau and their temporal relationships with the Cenozoic climatic changes.

Feeding range of age 1+ year Eurasian perch Perca fluviatilis in the Baltic Sea.

Using the widespread Eurasian perch Perca fluviatilis as a model organism, feeding ranges were investigated using stable-isotope ratios (δ15 N and δ13 C) and body condition. Differences were found between closely located sampling sites in a littoral area without obvious migration barriers, indicating that individual fish had small feeding ranges. Body condition differences between sampled stations were consistent over 4 years. Such sedentary behaviour is important to consider in, e.g. fisheries management and environmental monitoring, as local catch regulations may be meaningful or geographic stability in sampling locations may reduce noise in data.

Three new species of Plagioporus Stafford, 1904 from darters (Perciformes: Percidae), with a redescription of Plagioporus boleosomi (Pearse, 1924) Peters, 1957.

A form of Plagioporus Stafford, 1904 is described from the intestine of three North American species of darters (Perciformes: Percidae) from River West Twin, Wisconsin, USA, that we consider to be conspecific with Plagioporus boleosomi (Pearse, 1924) Peters, 1957 based on similarities in the sucker ratio, extent of the forebody, shape and position of the testes, vitellarium distribution and terminal genitalia. Three new species of Plagioporus are described from the intestine of darters as follows: Plagioporus fonti n. sp. from Percina nigrofasciata Agassiz in Florida, USA, Plagioporus limus n. sp. from Etheostoma squamosum Distler in Arkansas, USA and Plagioporus aliffi n. sp. from Etheostoma blennioides newmanni Miller in Arkansas, USA. Morphologically Plagioporus fonti n. sp., Plagioporus limus n. sp. and Plagioporus aliffi n. sp. are most similar to one another and to P. boleosomi, Plagioporus lepomis Dobrovolny, 1939 and 'P. etheostomae', a nomen nudum for a species described from Etheostoma blennioides Rafinesque in Kentucky, USA, all of which are collectively distinguished from congeners in having a combination of confluent vitellarium in the post-testicular space and absence of vitelline follicles with their entire length distributed in the forebody. Plagioporus fonti n. sp., P. limus n. sp. and P. aliffi n. sp. are respectively distinguished from one another and their closest congeners in having the anterior extent of the vitellarium in the anterior half of forebody to slightly anterior to the ventral sucker as opposed to one approximately at the level of the posterior margin of the ventral sucker, possession of an excretory vesicle reaching the anterior testis as opposed to one only reaching the posterior testis and having a longer than wide oral sucker and a wider than long ventral sucker. A Bayesian inference (BI) analysis of partial 28S rDNA sequences was conducted using the three new species and 24 sequences of opecoelids retrieved from GenBank, including ten species of Plagioporus. Plagioporus aliffi n. sp., Plagioporus fonti n. sp. and P. boleosomi comprised a moderately supported sister group to a clade containing all species of Plagioporus except Plagioporus limus n. sp. and Plagioporus shawi (Mcintosh, 1939) Margolis, 1970. Plagioporus limus and in turn P. shawi were resolved as sister to all other congeners with high and moderate support, respectively.

The accumulation of reproductive isolation in early stages of divergence supports a role for sexual selection.

Models of speciation by sexual selection propose that male-female coevolution leads to the rapid evolution of behavioural reproductive isolation. Here, we compare the strength of behavioural isolation to ecological isolation, gametic incompatibility and hybrid inviability in a group of dichromatic stream fishes. In addition, we examine whether any of these individual barriers, or a combined measure of total isolation, is predicted by body shape differences, male colour differences, environmental differences or genetic distance. Behavioural isolation reaches the highest values of any barrier and is significantly greater than ecological isolation. No individual reproductive barrier is associated with any of the predictor variables. However, marginally significant relationships between male colour and body shape differences with ecological and behavioural isolation are discussed. Differences in male colour and body shape predict total reproductive isolation between species; hierarchical partitioning of these two variables' effects suggests a stronger role for male colour differences. Together, these results suggest an important role for divergent sexual selection in darter speciation but raise new questions about the mechanisms of sexual selection at play and the role of male nuptial ornaments.

Warming alters the body shape of European perch Perca fluviatilis.

The consequences of elevated temperature on body shape were investigated by comparing European perch Perca fluviatilis from the Forsmark area of the Baltic Sea to P. fluviatilis from a nearby Biotest enclosure. The Biotest is a man-made enclosure within the Baltic Sea that has received warm water from a nuclear power plant since 1980, resulting in temperatures that are elevated 5-10 °C relative to the surrounding Baltic Sea. Sampled fish ranged from young-of-the-year to 14 years. Geometric morphometrics and multivariate statistical analysis revealed significant morphological differences between individuals of P. fluviatilis from these two habitats. Most importantly, relative shape changed with size, with small individuals of P. fluviatilis from Biotest being characterized by a deeper body shape and a larger caudal peduncle than the smaller Baltic individuals. In large specimens, smaller differences were found with Biotest individuals being more slender than Baltic individuals. These results show that, in order to have a full understanding of the biological effects of elevated temperatures, studies that cover the entire size range of organisms will be important. Apart from the direct influence of temperature on growth rate and body shape, other ecological factors affected by temperature are discussed as possible contributors to the observed differences between the two populations.

Evolution of the premaxillary fraenum and substratum in snubnose darters and allies (Percidae: Etheostoma).

Darters (Percidae: Etheostomatinae), a species-rich group of North American freshwater fishes, vary in the presence of a premaxillary fraenum, a strip of skin that connects the premaxillary bones to the snout, and it is hypothesized that this trait is a trophic adaptation to particular substrata. Ancestral state reconstructions and analyses of phylogenetic associations between presence of the premaxillary fraenum and preferred stream substratum were conducted in a clade of closely related darters (snubnose darters and allies) that vary in morphology and habitat preferences. The most recent common ancestor of this clade was inferred to possess a fraenum and to inhabit rocky substrata, consistent with previous hypotheses, but a significant correlation between fraenum presence and substratum type across the phylogeny was not found.

Rapid evolution of parasite resistance in a warmer environment: insights from a large scale field experiment.

Global climate change is expected to have major effects on host-parasite dynamics, with potentially enormous consequences for entire ecosystems. To develop an accurate prognostic framework, theoretical models must be supported by empirical research. We investigated potential changes in host-parasite dynamics between a fish parasite, the eyefluke Diplostomum baeri, and an intermediate host, the European perch Perca fluviatilis, in a large-scale semi-enclosed area in the Baltic Sea, the Biotest Lake, which since 1980 receives heated water from a nuclear power plant. Two sample screenings, in two consecutive years, showed that fish from the warmer Biotest Lake were now less parasitized than fish from the Baltic Sea. These results are contrasting previous screenings performed six years after the temperature change, which showed the inverse situation. An experimental infection, by which perch from both populations were exposed to D. baeri from the Baltic Sea, revealed that perch from the Baltic Sea were successfully infected, while Biotest fish were not. These findings suggest that the elevated temperature may have resulted, among other outcomes, in an extremely rapid evolutionary change through which fish from the experimental Biotest Lake have gained resistance to the parasite. Our results confirm the need to account for both rapid evolutionary adaptation and biotic interactions in predictive models, and highlight the importance of empirical research in order to validate future projections.

Transmission electron microscopy of the gastrointestinal tract of Nile perch Lates niloticus / Uso de microscopía electrónica de transmisión para visualizar el tracto gastrointestinal de la perca del Nilo Lates niloticus

The ultrastructure of the gastrointestinal tract of Nile perch was described using Transmission Electron Microscopy standard procedures. Investigations revealed the presence of mucous cells, blood vessels and oil droplets plus several nerve cells and muscle bundles in the oral cavity. Further observations revealed columnar epithelial cells in the oesophagus, with a ragged surface, high electron dense cytoplasm, intercellular spaces, mitochondria and mucus granules. The lamina propria of the oesophagus was composed of loose connective tissue, blood vessels, nerve cells and several leucocytes, while the muscularis externa was composed of striated muscle bundles with the a Z line, A band and I band. The stomach was characterized by mucosal glandular cells with electron dense granules, a prominent nucleus, mitochondria, and secretory canaliculi. The liver had an isotropic parenchyma composed of several hepatocytes with a single spherical euchromatic nucleus. The exocrine pancreatic cells in the liver occurred around large blood vessels, had large centrally positioned nuclei with electron dense nucleolus, electron dense granules, Rough Endoplasmic Reticulum, and mitochondria which dominated the cytoplasm of pancreatic cells.

La ultraestructura del tracto gastrointestinal de la perca del Nilo fue descrita utilizando un procedimiento estándar de Microscopía Electrónica de Transmisión (MET). Las investigaciones revelaron la presencia de células mucosas, vasos sanguíneos y pequeñas gotas de aceite, además de varias células nerviosas y haces musculares en la cavidad oral. Nuevas observaciones revelaron células epiteliales columnares en el esófago, con una superficie irregular, citoplasma elevado y electrodenso, espacios intercelulares, mitocondrias y gránulos mucosos. La lámina propia del esófago se compone de tejido conectivo laxo, vasos sanguíneos, células nerviosas y numerosos leucocitos, mientras que la muscular externa se compone de haces musculares estriados, con presencia de la línea Z, banda A y banda I. El estómago se caracteriza por presentar células glandulares mucosas con gránulos electrodensos , un núcleo prominente, mitocondrias y canalículos secretores. El hígado presentó un parénquima isotrópico compuesto de varios hepatocitos con un solo núcleo eucromático y esférico. Las células pancreáticas exocrinas se encontraron alrededor de grandes vasos sanguíneos, presentando grandes núcleos posicionados centralmente, con nucleólos densos, gránulos electrodensos en el retículo endoplasmático rugoso, y mitocondrias, que dominaron el citoplasma de las células pancreáticas.

Senescence-associated ß-galactosidase staining in fish cell lines and primary cultures from several tissues and species, including rainbow trout coelomic fluid and milt.

Cell lines and primary cultures from several teleost tissues and species were stained for senescence-associated ß-galactosidase (SA ß-Gal), revealing four general outcomes. (1) For long-standing fish cell lines that can be considered immortal, little or no SA ß-Gal staining was observed, regardless of the culture conditions. (2) For a new walleye cell line from the bulbus arteriosus (WEBA), most cells stained for SA ß-Gal even after 40 passages. This suggested that high SA ß-Gal activity was a unique property of WEBA, perhaps reflecting their endothelial character, rather than cellular senescence. (3) For cell lines developed from the walleye caudal fin and from somatic cells in rainbow trout coelomic fluid, no SA ß-Gal staining was observed in the earliest cultures to over 70 passages later. This suggested that cells from these anatomical sites do not undergo senescence in vitro. (4) By contrast, for cell lines developed from the walleye brain and from somatic cells in rainbow trout milt, most cells in the early-stage cultures stained for SA ß-Gal, but as these were developed into cell lines, SA ß-Gal-negative cells became dominant. This suggested that if cellular senescence occurred in vitro, this happened early in these cultures and subsequently a few SA ß-Gal-negative cells went onto to form the cell line. Overall, the presence of SA ß-Gal-positive cells in cultures could be interpreted in several ways, whereas their absence predicted that in these cultures, cells would proliferate indefinitely.