Wesley F. Porak

Seasonal relationship between gonadotropin, growth hormone, and estrogen receptor mRNA expression in the pituitary gland of largemouth bass

The objectives of this study were to investigate the seasonal changes in pituitary gonadotropins, growth hormone (GH), and estrogen receptor (ER) isoform mRNA in wild female and male largemouth bass (LMB) (Micropterus salmoides) from an unpolluted habitat to better understand reproductive physiology in this ecologically important species. Female pituitary luteinizing hormone (LH) beta subunit and follicle stimulating hormone (FSH) beta subunit mRNA showed significant seasonal variation with levels peaking from January to April and were lowest from May to August. Male LMB showed more variation in gonadotropin subunit expression from month to month. Females had approximately 2-3 times higher gonadotropin mRNA levels in the pituitary when compared to males. All three gonadotropin mRNAs in females were positively correlated to gonadosomatic index (GSI), but only LHbeta mRNA was correlated to GSI in males. Gonadotropin mRNA expression also increased with increasing oocyte and sperm maturation. Gonadotropin beta subunit mRNA expression was positively correlated to GH mRNA in both sexes. The expression of all three ER isoforms was significantly correlated to each other in both sexes. The concurrent increase in all three ER mRNA isoforms with increasing gonadotropin mRNA in females and males suggests a prominent role for E2 feedback on pituitary gonadotropin synthesis in both sexes and that each of the three ER isoforms are likely to play a role in the pituitary during teleost reproduction.

Time of Annulus Formation in Otoliths of Florida Largemouth Bass

Abstract Otoliths of Florida largemouth bass Micropterus salmoides floridanus were collected monthly from three Florida lakes to determine the time of annulus formation. Although some growth ring compaction was observed in March, annulus formation was not observed until April. Young fish (ages 2–3) and females tended to form annuli earliest. Annulus formation was complete in all populations by July. It is recommended that largemouth bass otoliths should be collected between July and March for aging purposes to eliminate confusion in interpretation of the last annulus.

Genetic Relationships among Populations of Florida Bass

Abstract Florida bass Micropterus floridanus are endemic to peninsular Florida and co-occur with largemouth bass M. salmoides in a natural intergrade zone in the northern portions of the state. In this study, we resolved the genetic population structure among populations of largemouth bass, Florida bass, and their interspecific hybrids from 48 lakes and streams across Florida, and we updated and refined the southernmost boundary of introgression. Nuclear (allozyme and microsatellite) and mitochondrial (restriction fragment length polymorphism) markers produced somewhat different results. Microsatellite genotypes alone and the combination of all nuclear genotypes resolved genetic structure among four regional groups within Florida: (1) northwest, (2) north-central, (3) central-west, and (4) south, central-east, and northeast. Allozyme genotypes alone did not resolve well-defined groups. The distribution of mitochondrial haplotypes suggested that populations from the St. Johns River drainage should be consi...

Identification and Transcriptional Modulation of the Largemouth Bass, Micropterus salmoides, Vitellogenin Receptor During Oocyte Development by Insulin and Sex Steroids

ABSTRACT Fish vitellogenin synthesized and released from the liver of oviparous animals is taken up into oocytes by the vitellogenin receptor. This is an essential process in providing nutrient yolk to developing embryos to ensure successful reproduction. Here we disclose the full length vtgr cDNA sequence for largemouth bass (LMB) that reveals greater than 90% sequence homology with other fish vtgr sequences. We classify LMB Vtgr as a member of the low density lipoprotein receptor superfamily based on conserved domains and categorize as the short variant that is devoid of the O-glycan segment. Phylogenetic analysis places LMB Vtgr sequence into a well-supported monophyletic group of fish Vtgr. Real-time PCR showed that the greatest levels of LMB vtgr mRNA expression occurred in previtellogenic ovarian tissues. In addition, we reveal the effects of insulin, 17beta-estradiol (E2), and 11-ketotestosterone (11-KT) in modulation of vtgr, esr, and ar mRNAs in previtellogenic oocytes. Insulin increased vtgr expression levels in follicles ex vivo while exposure to E2 or 11-KT did not result in modulation of expression. However, both steroids were able to repress insulin-induced vtgr transcript levels. Coexposure with insulin and E2 or of insulin and 11-KT increased ovarian esr2b and ar mRNA levels, respectively, which suggest a role for these nuclear receptors in insulin-mediated signaling pathways. These data provide the first evidence for the ordered stage-specific expression of LMB vtgr during the normal reproductive process and the hormonal influence of insulin and sex steroids on controlling vtgr transcript levels in ovarian tissues.

Isolation and characterization of eighteen microsatellite loci for the largemouth bass, Micropterus salmoides, and cross amplification in congeneric species

We used a PCR-based technique to isolate 18 microsatellite loci for the largemouth bass, Micropterus salmoides. These loci were characterized using sampled populations in Florida and Wisconsin. The mean number of alleles at a locus was 8 for the sample from Florida and 5 for the samples from Wisconsin. The observed heterozygosities were 0.57 and 0.33 for the samples from Florida and Wisconsin, respectively. There was evidence of genetic differentiation between the Florida and Wisconsin samples at all 18 loci, indicating spatial structure within the range of M. salmoides. The markers cross-amplified in the seven other micropterid species, which suggests they would have utility for studies of hybridization among other members of the genus.

Effects of Surgically Implanting Radio Transmitters in Juvenile Largemouth Bass

AbstractRecent advances in the technology of miniature radio transmitters have allowed researchers to study smaller fish, including juveniles, for which behavioral information is lacking. Transmitters selected should have minimal effects on tagged fish so that inferences may be made about untagged individuals. Our objective was to evaluate the short-term effects of surgically inserted dummy transmitters (1.2–2.7% of the fishs body weight) on growth and predator avoidance in 90–120-mm hatchery-reared Largemouth Bass Micropterus salmoides. We compared growth and predator avoidance between tagged and untagged (control) fish in tanks. Mortality of tagged and control fish was variable by tank and was most commonly caused by columnaris, a fish disease widespread in aquaculture. A slight impairment of growth for tagged fish (difference of as much as 1.19% body weight gained per day) was observed during experiments run for 21 and 30 d. At the conclusion of each growth experiment, most fish had shed their suture ...

Economic and Conservation Impacts of Stocking Wild Florida Bass into Large Florida Lakes

AbstractSupplemental stocking of fingerling or advanced fingerling Largemouth Bass Micropterus salmoides is a common management strategy for augmenting natural production in low-recruitment systems. Few studies, however, have evaluated the impact of stocking adult bass taken from donor lakes. Over a period of 6 years, University of Florida researchers stocked Florida Lakes Griffin and Dora with 24,781 wild Florida Bass M. s. floridanus collected by electrofishing from other Florida lakes. During stocking years, stocked fish made up to 10% of the population in Lake Griffin and 27% in Lake Dora from electrofishing samples. However, 1 year after all stocked fish had been released, the proportion of stocked bass had declined to less than 5%, and 3 years after it had declined to less than 1%. We did not detect an increase in recruitment (catch of age-1 bass) following stocking, so any benefit from stocking was likely short-lived. We also could not conclude that stocking was responsible for increasing fishing e...

Oocyte Development and Staging in the Florida Bass, Micropterus floridanus (LeSueur, 1822), with Comments on the Evolution of Pelagic and Demersal Eggs in Bony Fishes

Oocyte development and staging is described from histological preparation of the ovaries of field collected specimens of the Florida Bass, Micropterus floridanus. Oocyte development in Florida Bass progresses through six stages beginning with oogonial proliferation and ending with ovulation, the release of eggs. The stages are based on mitosis and meiosis, the core processes of Adaptable Oocyte Staging. After ovulation, the postovulatory follicle complex produces a mucus-like fluid with unknown function; we speculate that it protects the eggs immediately upon ovulation and upon their release into freshwater during spawning. Atresia is rare in the ovaries of reproductive Florida Bass. The release of cortical alveoli after fertilization follows a unique, extended time-release sequence. Oocyte development in the freshwater perciform Florida Bass follows precisely a pattern that has been documented for marine perciform fishes that produce positively buoyant, pelagic, non-adhesive eggs. The eggs of Florida Bass are morphologically like these pelagic eggs in that they have a single large oil globule and no attachment filaments. Yet Florida Bass eggs have small, clear yolk globules and an adhesive egg envelope and are functionally demersal. Thus, classification of an egg as pelagic or demersal should consider its morphology as well as its function, especially if egg type is to be used to interpret phylogenetic relationships or evolutionary patterns. The clearing of yolk due to the uptake of water during the development of actinopterygian eggs, as they progress from a demersal to a potentially pelagic phase, may be a general mechanism of oocyte maturation in teleost fishes.