Paul S. Wills

Use of Ultrasound Imaging to Determine Sex of Shovelnose Sturgeon

Abstract During November 2002, 51 shovelnose sturgeon Scaphirhynchus platorynchus were sexed by ultrasound imaging using a portable ultrasonograph. We identified males with 96% accuracy (N = 25) and females with 80% accuracy (N = 25); one hermaphroditic individual was misidentified as a male. Overall, ultrasound imaging was 86% accurate. Sex in postspawned females was difficult to determine, 60% being misidentified as males (N = 5). Ultrasonography is an effective noninvasive method for sex determination that can be applied to other species of Acipenseriformes. Modern portable equipment expands its utility to field studies.

Habitat Use by Middle Mississippi River Pallid Sturgeon

Abstract Little is known about the habitat preferences and needs of pallid sturgeon Scaphirhynchus albus, which was federally listed as endangered in 1990. To learn more about habitat use and selection by pallid sturgeon, sonic transmitters were surgically implanted in 27 individuals from the middle Mississippi River. Study fish were located 184 times (1–23 times/individual) from November 1995 to December 1999. Of the seven macrohabitats identified, pallid sturgeon were found most often in main-channel habitats (39% of all relocations) and main-channel border habitats (26%); the between-wing-dam habitats were used less often (14%). Strausss linear selectivity index (Li ) values indicated that study fish exhibited positive selection for the main-channel border, downstream island tips, between-wing-dam, and wing-dam-tip habitats; they showed negative selection for main-channel, downstream of wing dams, and upstream of wing dam habitats. Comparison of Li values for four temperature ranges and three daily me...

Flowing Water: An Effective Treatment for Ichthyophthiriasis

Abstract Ichthyophthiriasis, or ich, is a disease of freshwater fish that is difficult to treat chemotherapeutically because the causative agent, Ichthyophthirius multifiliis, is protected by the hosts epithelium during much of its life cycle. In our experiments, a modified standard formalin treatment (25 mg/L for 4 h, 4 d/week) conferred partial protection but failed to prevent 40–70% mortality among channel catfish Ictalurus punctatus. A water velocity of 20.3 cm/min in 5-m-long raceways and a turnover rate of 2.5/h reduced mortality of ich-infected channel catfish fingerlings to less than 10%. A water velocity of 36.5 cm/min and a turnover rate of 4.5/h held mortalities to 7% and eliminated ich from the raceways. When turnover rate fell below 1.9/h (water velocity 85 cm/min, turnover rate > 2.1/h) resulted in no losses caused by ich during 2 years a...

Age and growth of the bighead carp Hypophthalmichthys nobilis (RICHARDSON 1845) in the middle Mississippi River

An age and growth study was conducted on the bighead carp Hypophthalmichthys nobilis population from the middle Mississippi River (MMR) using pectoral fin ray cross-sections. Bighead carp (N = 92) were collected from the MMR and from Pool 26 (N = 40) during 1998 and spring of 1999 using trammel and gill nets, AC electrofishing, and seining. Length-frequency distributions were dominated by the 800-900 mm length class in both the MMR and Pool 26. Age classes 1-6 were represented in the MMR sample, and only ages 4-6 in the Pool 26 sample. Age 4 (1994 year class) was dominant in 1998 in the MMR. The mean condition factor (K) was 1.03 for all bighead carp collected, and ranged from 0.58 to 2.04. Condition factor was significantly higher for Pool 26 than for the MMR (ANOVA; p ≤0.0001), but not significantly different between sexes (ANOVA; p = 0.60). Condition factor peaked in May and decreased sharply during June and July of 1998. An unconstrained von Bertalanffy growth equation was obtained. Growth was fast in both the MMR and Pool 26, but no significant differences in relative or absolute growth were found between the two populations. Bighead carp is much more abundant in the MMR than reported in the literature or commercial fisheries harvest reports. Recruitment of bighead carp from the MMR was not consistent, but fast growth (reaching 1 kg by age 2), and high abundance suggest that a commercial fishery for bighead carp could be sustained in the MMR.

Reduced Reproductive Capacity in Diploid and Triploid Hybrid Sunfish

Abstract Reproductive capacity of 2-year-old sibling green sunfish Lepomis cyanellus male × bluegill L. macrochirus female diploid and triploid hybrids was investigated using histology and flow cytometry. Gonads of triploid females were immature compared with diploids, and gonads possessed cells that primarily appeared to be oogonia or immature oocytes; most cells were triploid. Gonadal development in triploid males appeared to be more advanced (based on observed cell types) than development in triploid females, although male triploids failed to yield milt during stripping. Some spermatozoa in triploid testes were completely differentiated, having tails. No cells, however, were less than 3n and most were 6n, which indicates that meiosis is interrupted at the first reduction division in male triploids but that some cells did complete spermiogenesis. Diploid male hybrids possessed a small proportion of haploid cells, and spermatozoa in their testes appeared normal. The largest proportion (more then 60%) of ...

Effects of repetitive formalin treatments on channel catfish juveniles

Abstract Channel catfish Icialurus punctatus ranging from 70 to 148 mm in total length were treated with formalin at a concentration of 25 μL/L for 4 h daily on four successive days each week over a 28-week period beginning in mid-September. Coefficients of condition (weight-tolength ratios) and histological examinations of gill tissues were used to evaluate health of fish exposed to formalin. Gill tissues of both formalin-treated and untreated fish showed effects typical of intensive culture, including hypertrophy, hyperplasia, and excess mucous secretion; no differences were found in gill morphometry between the two groups. Channel catfish periodically treated with formalin had a significantly higher coefficient of condition (P < 0.05) after 28 weeks and no indication of adverse effects attributable to formalin.

Range Expansion for the Golden Topminnow, Fundulus chrysotus (Günther), and it Rediscovery in Missouri

ABSTRACT Six golden topminnow (Fundulus chrysotus) specimens were collected in Mississippi County, Missouri in 1997. This is the most northern location on record for the species. F. chrysotus is currently listed as extirpated in Missouri, but it should now be reconsidered for endangered status in the state. Because of a planned flood control project in the area of these collections the future of this species in Missouri is uncertain.