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Preliminary description of lesions in juvenile largemouth bass injected with largemouth bass virus.

Juvenile largemouth bass Micropterus salmoides were intraperitoneally injected with largemouth bass virus (LMBV), a member of the genus Ranavirus, family Iridoviridae. Moribund fish which had been injected with 10(6.2) tissue culture infectious doses, 50% endpoint (TCID50), were sampled 4 d after injection; other largemouth bass injected with this dose died between 3 and 5 d after injection. Fish injected with 10(2.8) TCID50 of LMBV were also examined after 4 d and had lesions similar to those of fish injected with the high dose. Clinical signs included darker pigmentation, inflammation and necrosis at the site of injection, distended abdomen, corkscrew swimming, and lateral recumbency. Internally, fish had focally pale livers, bright red spleens and reddened intestinal ceca. Histologically acute fibrinous peritonitis affected the surface of all organs in the peritoneal cavity, but deeper portions of organs appeared normal. There was also necrosis of the gastrointestinal mucosa. Except for the injection site, lesions were confined to the peritoneal cavity.

Animals↗

Protein requirements of smallmouth bass and largemouth bass.

Protein requirements of young smallmouth and largemouth bass reared near ideal water temperatures were estimated as an initial step in quantifying specific nutrients essential to these fishes. Test fish were conditioned to accept pelleted rations, reared in small circular tanks and fed all they would easily consume at each feeding. Six levels of dietary protein were evaluated and gross energy of test diets ranged from 4,219 to 4,793 kcal per kilogram dry diet. Almquist-type plots were used to identify minimum protein requirements and maximum rates of growth. Minimum protein requirements of age 0 and 1 smallmouth bass were 45.3 and 45.2% of the dry diet and maximum rates of growth were 2.85 and 0.99% per day. In age 0 and 1 largemouth bass minimum protein requirements were not greater than 39.9 and 40.8% of the dry diet and maximum rates of growth were 2.36 and 0.76% per day. Protein utilization was measured in age 0 smallmouth and largemouth bass and dietary efficiency was measured in each group of bass. These statistics corroborate the estimated minimum protein requirements.

Amino Acids, Essential↗

Exposure to p,p'-DDE or dieldrin during the reproductive season alters hepatic CYP expression in largemouth bass (Micropterus salmoides).

Largemouth bass (LMB) in Central Florida living on sites with high levels of organochlorine pesticides (OCPs) have exhibited poor reproductive success and altered steroid profiles. The mechanism underlying these changes is unknown, however changes in the rate of steroid metabolism could alter steroid homeostasis. Members of the CYP2 and CYP3A families play a significant role in the metabolism of many xenobiotics and endogenous compounds, including sex steroids. Therefore, the goal of this study was to identify members of the CYP2 and CYP3A families in LMB and characterize the effects of OCP exposure on their expression. Full-length clones of two CYP3A isoforms were obtained from LMB liver, CYP3A68 and 3A69, which exhibited significant sequence divergence. Full-length clones for CYP2N14 and CYP2P11 were also obtained from LMB liver. Steady-state mRNA levels of each of these CYPs increased in both sexes between early reproductive phase (December) and peak reproductive phase (March). Expression of CYP3A68 and CYP2P11 was sexually dimorphic during peak reproductive phase with 2-fold higher expression in females and males, respectively. Foodborne exposure to 46 ppm p,p'-DDE or 0.8 ppm dieldrin for 30 days did not have a significant effect on expression of CYPs. However, 4 months exposure to p,p'-DDE induced CYP3A68 and 3A69 expression in both sexes, while dieldrin produced weak induction of CYP3A68 and suppressed CYP3A69 expression in females, but had no effect on males. Neither p,p'-DDE nor dieldrin significantly altered the expression of CYP2P11 or CYP2N14. This work demonstrates that there are significant changes in CYP expression that occur during LMB reproduction which can be modified by exposure to OCPs.

Amino Acid Sequence↗

A multi-model genome-wide association study identifies genetic variants underlying resistance to Largemouth Bass Ranavirus (LMBV) in Micropterus salmoides.

Largemouth bass (Micropterus salmoides) is an economically important freshwater aquaculture species, yet recurrent outbreaks of Largemouth Bass Ranavirus (LMBV) continue to impair production and cause substantial losses. The genetic basis of host variation in LMBV resistance remains insufficiently characterized. Here, we applied a multi-model genome-wide association study (GWAS) to identify loci associated with resistance following a controlled challenge with the LMBV-23PY strain. Whole-genome resequencing was performed for 146 phenotyped fish, including 72 susceptible and 74 resistant individuals. After stringent quality control, 877,262 high-quality variants were retained and tested using six GWAS models. Across binary survival status and survival time phenotypes, 32 shared suggestive variants were consistently detected across models, representing suggestive loci for LMBV-23PY resistance. Genes within ±50 kb of these loci were annotated, and functional enrichment highlighted immune- and redox-related biological processes. Three prioritized candidates-GSTT3L (glutathione S-transferase theta-3-like), CGRP2 (calcitonin gene-related peptide 2), and NPPC (natriuretic peptide C)-were associated with pathways involved in oxidative stress responses and immune regulation. Collectively, these results provide insight into the genetic architecture of LMBV-23PY resistance in largemouth bass and identify suggestive variants and associated candidate genes for downstream validation, functional interrogation, and the development of marker-assisted and genome-enabled breeding strategies.

Animals↗

Molecular characterization of a ranavirus isolated from largemouth bass Micropterus salmoides.

An iridovirus, isolated from largemouth bass Micropterus salmoides following a die-off among adult fish and provisionally designated largemouth bass virus (LMBV), was characterized by analysis of viral protein synthesis in infected cells, viral DNA restriction fragment length polymorphisms (RFLP), and sequence determination of the major capsid protein and viral DNA methyltransferase genes. All 3 approaches yielded results consistent with the suggestion that LMBV was a member of the genus Ranavirus. Moreover, LMBV was nearly identical to 2 isolates from Southeast Asia which had been previously detected in imported ornamental fish. It remains to be determined whether infection of largemouth bass resulted from exposure to an imported virus, or whether the presence of similar viruses in southeast Asia and the southeastern United States indicates that iridovirus species are not geographically limited as suggested earlier, but rather globally distributed.

Amino Acid Sequence↗

Potential of largemouth bass as vectors of 137Cs dispersal.

We conducted a radio telemetry study on the movements of potentially contaminated largemouth bass between Steel Creek, a restricted access (137)Cs contaminated stream on the Savannah River Site (located in South Carolina, USA), and the publicly accessible Savannah River. Largemouth bass were relatively mobile in lower Steel Creek and the portion of the Savannah River near Steel Creek, and there was considerable movement between these two habitats. Largemouth bass had home ranges of about 500 linear meters of shoreline in the Savannah River but sometimes moved long distances. Such movements occurred primarily during the spawning season, largely upstream, and increased when water levels were changing or elevated. However, approximately 90% of the largemouth bass observations were within 10 km of Steel Creek. The total quantity of (137)Cs transported into the Savannah River by largemouth bass was much less than transported by water and suspended sediments discharged from Steel Creek. We conclude that largemouth bass from the Savannah River Site are unlikely to be responsible for long distance dispersal of substantial radiological contamination in the Savannah River.

Animal Migration↗

Failure of low-velocity swimming to enhance recovery from exhaustive exercise in largemouth bass (Micropterus salmoides).

This study was intended to discover whether forcing largemouth bass (Micropterus salmoides) to swim at 0.5 body lengths/second following exercise would expedite recovery relative to fish recovered in static water. Exercise resulted in a suite of physiological disturbances for largemouth bass that included a depletion of anaerobic energy stores, an accumulation of lactate, and increased cardiac output. At 1 h following exercise, exhaustively exercised largemouth bass forced to swim exhibited expedited recovery relative to fish in static water, evidenced by lower concentrations of lactate in white muscle, elevated concentrations of phosphocreatine in white muscle, and reduced concentrations of glucose in plasma. By 4 h postexercise, largemouth bass forced to swim during recovery exhibited signs of physiological disturbance that were absent in fish recovered in static water. These signs of disturbance included a loss of osmotically active particles from plasma, elevated lactate in plasma, reductions of phospocreatine in white muscle, and increased cardiac output. These results are discussed in relation to the body of work with salmonid fishes showing physiological benefits to recovering fish in flowing water.

Animals↗

Modeling of gene expression pattern alteration by p,p'-DDE and dieldrin in largemouth bass.

In this study, largemouth bass (LMB) were subchronically exposed to p,p'-DDE or dieldrin in their diet to evaluate the effect of exposure on expression of genes involved in reproduction and steroid homeostasis. Using real-time PCR, we detected a different gene expression pattern for each OCP, suggesting that they each affect LMB in a different way. We also detected a different expression pattern among sexes, suggesting that sexes are affected differently by OCPs perhaps reflecting the different adaptive responses of each sex to dysregulation caused by OCP exposure.

Animals↗

Morphological and physiological correlates with swimming performance in juvenile largemouth bass.

Winter- and summer-acclimatized largemouth bass (Micropterus salmoides) were collected from hatchery ponds in eastern Colorado during late winter and midsummer, then challenged with two prolonged swimming performances (step test and constant-velocity endurance). Variation in the step test performances was significantly correlated with variation in the endurance performances in the winter-acclimatized but not in the summer-acclimatized fish. Fourteen physiological and morphological traits were measured on each fish, and correlations among these traits and swimming performance were tested. None of the traits measured were correlated with performance variation in both the winter- and summer-acclimatized fish. The only significant correlate with swimming performance in the summer-acclimatized fish was white muscle lactate dehydrogenase activity (n = 19). Six of the seven factors correlating with winter swimming performance (n = 18-19) could be divided into two categories: traits associated with fasting (condition factor and liver enzymatic activity) and those associated with oxygen delivery (heart mass, heart and red muscle cytochrome oxidase activity). The results of this study suggest that morphological and physiological correlates of swimming performance in juvenile largemouth bass are profoundly influenced by seasonal variation.

Acclimatization↗

PCR method for detection of largemouth bass virus.

A polymerase chain reaction (PCR) method was developed for largemouth bass virus (LMBV). This iridovirus can cause a lethal disease of largemouth bass Micropterus salmoides, but also subclinically infects largemouth bass and other species of fishes. Oligonucleotide primers were designed to specifically amplify the major capsid protein gene of LMBV. The protocol for sample processing and PCR provided a method that was more sensitive than cell culture for detection of LMBV in fish. The specific amplification of LMBV also provided an improved method for confirming the identity of cell-culture isolates presumptively identified as LMBV.

Animals↗

Interaction of bass tapeworm, Proteocephalus ambloplitis, and Neoechinorhynchus sp. (Acanthocephala) in largemouth bass, Micropterus salmoides.

The number of plerocercoids of the bass tapeworm, Proteocephalus ambloplitis, in wild largemouth bass was negatively correlated (r = -0.94) with the number of Neoechinorhynchus sp. Competitive inhibition between the 2 parasites appeared to exist. Similarly, the numbers of Neoechinorhynchus sp. in wild bass decreased when adult bass tapeworms were present in the intestine. Proteocephalus ambloplitis plerocercoids used to challenge bass vaccinated with either P. ambloplitis adult or Neoechinorhynchus sp. antigens were smaller (P less than 0.05) when recovered than those used to challenge control bass. Based on preliminary results, both antigens might have enabled the bass to limit growth and/or development of the invading bass tapeworm, plerocercoids. Cross-protective immunity may be the reason for this occurrence, in which case, it could offer an explanation for competitive inhibition existing between P. ambloplitis and Neoechinorhynchus sp.

Acanthocephala↗

Mercury accumulation in largemouth bass (Micropterus salmoides) in a Florida lake.

Rates of mercury accumulation were examined in male and female largemouth bass (Micropterus salmoides) from Lake Tohopekaliga, Florida, to establish methods for fish consumption advisories for the protection of human health. In addition, concentrations were determined in five lower trophic level fish species. Total mercury concentrations in adult largemouth bass muscle tissue ranged from 0.16 to 1.10 micrograms/g (fresh weight) and increased as fish increased in size and age. Whole-body mercury concentrations of 1990 year-class largemouth bass increased from 0.05 microgram/g at 20 mm and to 0.32 microgram/g at 320 mm (age 2). Significant differences were found in the rates of accumulation between sexes for length and weight, but not for age. Therefore, standardized mercury concentrations were determined using bass age to make comparisons among sampling dates. Although there were significant differences in adjusted mean mercury concentrations among two sampling dates, mercury content of standard-age bass remained relatively constant over time. Largemouth bass exceed the Florida Health Advisory level for limited consumption of fish (0.50 microgram Hg/g) based on a mean concentration of 0.59 microgram/g for 64 bass. Advisories based on fish morphological characteristics (i.e., length, weight) or age are not possible for Lake Tohopekaliga due to differences in mercury accumulation in male and female bass. Lower trophic level species of sport fish did not exceed the limited consumption level.

Animals↗

Waterborne and dietary hexavalent chromium exposure causes DNA-protein crosslink (DPX) formation in erythrocytes of largemouth bass (Micropterus salmoides).

Formation of DNA-protein crosslinks (DPXs) was demonstrated in erythrocytes from fathead minnows (Pimephales promelas) and largemouth bass (Micropterus salmoides) exposed to hexavalent chromium [Cr(VI)], a known carcinogenic and mutagenic metal contaminant of many industrial waterways. Tank water exposure of 2-3 in. fathead minnows to 2 ppm Cr(VI) led to significant DPX formation in erythrocytes, with over 140-200% elevations above background levels at 3-4 days, respectively. Largemouth bass exposed similarly were found to have 62% elevation of DPX levels after 4 days. When largemouth bass were fed a diet of minnows injected with 20 microg Cr(VI) for 5 days, a significant (p<0.01) increase of DPXs in erythrocytes was observed, with 80% elevation above erythrocytes from bass fed minnows injected only with saline. However, when largemouth bass were fed a diet exclusively of minnows exposed to 2 ppm Cr(VI) for 21 days, there was no significant difference in DPX levels compared to bass fed control (unexposed) minnows. This study provides evidence that DPX formation occurs in erythrocytes of fathead minnows exposed under controlled conditions to low ppm Cr(VI) concentrations, which is at or below concentrations previously assigned no observable effect levels. Furthermore, it appears that both waterborne and high dose dietary exposure to Cr(VI) can lead to DPX formation in erythrocytes of predatory fish species such as bass. However, it is unlikely that a bioconcentration of chromium in the food chain would be a major concern at these low ppm levels of exposure. Further, it may be difficult to achieve dietary Cr(VI) levels high enough to elicit DPXs in predatory fish under most environmental exposure scenarios.

Animals↗

Citrate ions enhance taste responses to amino acids in the largemouth bass.

The glossopharyngeal (IX) taste system of the largemouth bass, Micropterus salmoides, is highly selective to amino acids and is poorly responsive to trisodium citrate; however, IX taste responses to specific concentrations of L- and D-arginine and L-lysine but not L-proline were enhanced by citrate but not sodium ions. Binary mixtures of L-arginine (3 x 10(-4)M and 10(-3)M) or D-arginine (10(-3)M) + trisodium citrate (10(-3)M; pH 7-9) resulted in enhanced taste activity, whereas binary mixtures of higher concentrations (10(-2)M and 10(-1)M) of L- or D-arginine + 10(-3)M trisodium citrate were not significantly different from the response to the amino acid alone. Under continuous adaptation to 10(-3)M citrate, taste responses to L-arginine were also enhanced at the identical concentrations previously indicated, but responses to 10(-2)M and 10(-1)M L-arginine were significantly suppressed. Under continuous adaptation to 10(-2)M L-arginine, taste responses to 10(-2)M, 10(-1)M, and 10(0) M citrate were significantly enhanced. Cellular concentrations of both citrate and amino acids in prey of the carnivorous largemouth bass are sufficient for this taste-enhancing effect to occur naturally during consummatory feeding behavior. Citrate acting as a calcium chelator is presented as a possible mechanism of action for the enhancement effect.

Adaptation, Physiological↗

First isolation of largemouth bass virus.

The first reported fish kill caused by largemouth bass virus (LMBV) occurred in 1995 in Santee-Cooper Reservoir, South Carolina, USA. Subsequently, this iridovirus has been implicated in additional fish kills and has also been found in clinically healthy fish in numerous locations in the southeastern USA. We compared the virus from Santee-Cooper Reservoir with a virus isolated in 1991 from large-mouth bass, Micropterus salmoides, from Lake Weir, Florida. Restriction fragment length polymorphisms and the DNA sequence of a portion of the major capsid protein gene were identical for the South Carolina and Florida isolates. These results establish that LMBV was first found in Florida, rather than South Carolina. We propose that the name largemouth bass virus continue to be used for this virus, rather than alternative names based on geographical origin.

Animals↗

Genetic monogamy and biparental care in an externally fertilizing fish, the largemouth bass (Micropterus salmoides).

Breeding, male North American sunfish (Centrarchidae), are often brightly coloured and promiscuous. However, the largemouth bass (Micropterus salmoides) is sexually monomorphic in appearance and socially monogamous. Unlike some other nest-tending centrarchids in the genus Lepomis, largemouth bass have also been reported to provide biparental care to eggs and fry. Here we use microsatellite markers in order to test whether social monogamy predicts genetic monogamy in the largemouth bass. Offspring were collected from 26 nests each usually guarded by a pair of adults, many of which were also captured. Twenty-three of these progeny cohorts (88%) proved to be composed almost exclusively of full-sibs and were thus the product of monogamous matings. Cuckoldry by males was rare. The genetic data also revealed that some nests contain juveniles that were not the progeny of the guardian female, a finding that can be thought of as low-level 'female cuckoldry'. Overall, however, the data provide what may be the first genetic documentation of near-monogamy and biparental care in a vertebrate with external fertilization.

Animals↗

Functional significance of the co-localization of taste buds and teeth in the pharyngeal jaws of the largemouth bass, Micropterus salmoides.

Studies of feeding behavior in the largemouth bass, Micropterus salmoides, revealed that live goldfish or artificial food balls are ingested in three discrete steps: inhalation of the food into the oral cavity, passage through the pharyngeal cavity, and swallowing. Food balls with or without a feeding stimulant were inhaled with equal frequency; thus, vision was clearly the major sense affecting inhalation. However, food balls with defined concentrations of a feeding stimulant were swallowed in a dose-dependent manner, whereas food balls without a feeding stimulant were promptly expelled. Thus, gustation played a major role in stimulating swallowing. Videotaped observations of feeding behavior suggested that both food processing and gustation occur in the pharynx and take place before the swallowing of either goldfish or food balls. The well-developed pharyngeal jaws of largemouth bass consist of six major pads of caniform teeth in the upper pharynx and two pads in the lower pharynx. Scanning electron microscopy showed that taste buds were abundant around most of these pharyngeal teeth. Histological sections prepared from all pharyngeal pads revealed that both elevated and flattened taste buds occur with the teeth. The morphology of these taste buds was typical of that described in other teleosts. Neuronal profiles, visualized with an HNK-1 monoclonal antibody, were observed entering each taste bud. The antibody also selectively stained a group of one to four putative sensory cells in each taste bud and the distal processes of these cells in the receptor area. The co-localization of teeth and taste buds on the pharyngeal jaws indicates that food processing and gustation both occur there, and that together these processes determine whether a potential food item is swallowed.

Animals↗

Occurrence of acanthocephalans in largemouth bass and smallmouth bass (Centrarchidae) from Gull Lake, Michigan.

A total of 65 largemouth bass, Micropterus salmoides, and 27 smallmouth bass, M. dolomieu, collected in April-September 2000 and April-July 2001 from Gull Lake, Michigan, were examined for acanthocephalans. Leptorhynchoides thecatus and Neoechinorhynchus cylindratus infected all the bass examined. Leptorhynchoides thecatus had the highest mean intensity (258.2 +/- 185.4 in 2000 and 145.0 +/- 61.0 in 2001) of the species infecting smallmouth bass. Although N. cylindratus had higher mean intensities (42.1 +/- 37.9 in 2000 and 68.9 +/- 70.5 in 2001) than did L. thecatus in largemouth bass, the values were not significantly different between bass species. The prevalence, mean intensity, and mean abundance of Pomphorhynchus bulbocolli in the bass species were below the values for the other acanthocephalan species. Leptorhynchoides thecatus and N. cylindratus are the most abundant intestinal helminths in bass from Gull Lake.

Acanthocephala↗