Courtenay, Walter R. Jr.

The growth and structure of the pseudobranchs of
Trachinotus carolinus and Oligoplites saurus is
described, illustrated, and discussed with respect to
their histology and gross morphology.
Morphological and histological differences between
the pseudobranchs of the two species occur in the
associated arteries, filament growth, mitochondrial
form, and in the epithelium bordering the pseudobranchs.
The pseudobranch of T. carolinus is contrasted with a
typical carangid pseudobranch, characterized by O. saurus
is thick and heavily vascularized and shows a tendency to
atrophy with growth of the fish.
The results of bilateral pseudobranchectomy
differed between adults and juveniles. All the fish
became blind; however, only the adults displayed
buoyancy problems and permanent chromatophore expansion.

Meristic and morphometric characteristics as well as isoelectric focusing and two-dimensional electrophoretic protein banding patterns of Scomberomorus cavalla were investigated in an attempt to find a technique to adequately identify Atlantic and Gulf of Mexico migratory groups, respectively, in the southeast Florida mixing zone. Data were collected from king mackerel from three locations: Riviera Beach, Palm Beach County; St. Petersburg, Pinellas County; and Panama City, Bay County; Florida. Morphometric and electrophoretic differences in samples from St. Petersburg, may indicate that the fish collected in this region constitute a separate stock. Nevertheless none of these techniques was conclusive enough to be adequate in separating these fish stocks for management purposes.

The density and diversity of fishes of the Kissimmee River Floodplain have been affected by channelization of the Kissimmee River. Reduced hydrology, human encroachment, and overall loss of habitat appear to have reduced the level of fish diversity and density within the floodplain of the Kissimmee River. This landmark study collected vegetative habitat and fish population density and diversity data within the altered floodplain for baseline information prior to initiation of river restoration activities in the form of dechannelization. Secondary studies included poecillid fecundity data as well as a localized rotenone study within the previously restored am of Pool B. Overall results of the study indicate that post restoration floodplain fish collection studies should reveal increased fish density and diversity within the expanded and restored floodplain habitat.

Floodplains are important elements of river-floodplain systems. Numerous riverine fishes utilize floodplain habitats for reproduction, feeding, and protection. Largemouth bass and bluegill sunfish were tracked using radiotelemetry, and environmental parameters were measured at fish locations. Bass and bluegill used habitats with the same physical and chemical characteristics. Floodplain habitats were utilized frequently, as much as main river channel habitats. Fishes used habitats dominated by vegetation, with sand substrates, and that were more stable with regard to environmental conditions. Largemouth bass were more mobile than bluegill sunfish. Fish movements may have been in response to unfavorable environmental conditions, as more mobile fishes were associated with higher water temperatures and lower concentrations of dissolved oxygen.

Channelization of the Kissimmee River from 1962 to 1971 altered the natural hydrology of the river/floodplain system. Results of construction of the C-38 canal included loss of continuous flow of water and loss of floodplain habitat which adversely impacted the fish community. In 1984 the South Florida Water Management District (SFWMD) constructed the Pool B demonstration project to evaluate the feasibility of a planned restoration project. To evaluate success of the demonstration project in enhancing the Pool B fish fauna, a hoop net sampling program was conducted in 1996. The data suggest that black crappie (Pomoxis nigromaculatus) and other sport species in Pool B are benefiting from habitat enhancements resulting from the demonstration project. Additional analysis distinguishes black crappie as the only centrarchid sampled that maintains activity during nocturnal hours. Bluegill (Lepomis macrochirus) were most active during May sampling when water temperatures were optimal for spawning.

Rock and coral reef fishes are known to select their habitat, and selection oftentimes involves the settlement of pelagic larval stages. Thus, I examined the short-term temporal relationship between artificial reef morphology and the composition of warm-water reef fish assemblages 30 m offshore of the Town of Palm Beach, Florida. Correlations were found between reef height and total fish abundance and species richness. Reef height was also correlated with log transformed numbers of juveniles. Horizontal opening size showed an inverse correlation with species richness and a weak inverse trend with juvenile abundance. Furthermore, vertical openings were directly proportional to juvenile and total fish abundance, and to species richness. Piscivore abundance was weakly influenced by presence and dimensions of vertical crevices. Thus, artificial reefs with many varied-sized vertical crevices are most desirable for attracting juvenile warm-water reef fishes.

Small clear and blackwater streams of the neotropics are economically important because they may be nursery grounds for important food and aquarium fishes. At present, these ecosystems are being negatively impacted by current logging, and gold and diamond mining practices. Thus, the role of biotic and abiotic factors in fish community structure was examined in three unimpacted streams in Guyana, South America. These streams had relatively low fish species diversity, but complex feeding guild structure. No significant correlations between abiotic factors and fish species diversity and feeding guild diversity were determined due to small sample size. However, principal component analysis suggested an association between pH and species diversity, and conductivity and guild diversity. Biotic factors, such as competition and predation may be the primary determinant of fish community structure and organization in neotropical blackwater streams.

Gradual salinity acclimatization and growth studies were performed on fry of the spotted tilapia, Tilapia mariae. First, fry were successfully brought to a salinity of 40%. in 8 weeks by gradual weekly increments of 5 %.. Second, fry were exposed separately for nine weeks to salinities of 0, 5, 10, 20, 25, and 30 %.. Fish grew best at 5 and 10 %. (p < 0.05) and least at 30 %.. At nine weeks, fish at 0, 5, 10, 20, 25, and 30%. appeared to be osmoregulating, as indicated by osmolarities of their inner body fluids. These results suggest that Tilapia mariae may become a competitive threat to fishes in native estuarine environments in southern Florida.

Two gynogenetically reproducing unisexuals, the diploid Poecilia
formosa and its associated triploid are sympatric to P. mexicana, a
bisexual species, in northeastern Mexico. All compete for sperm from
P. mexicana males. Field and laboratory experiments studied habitat.
preferences and associations as mechanisms of reducing competition. A
new tagging method was developed.
Laboratory results (Phase One) indicated habitat preferences of
each female type. Further studies (Phase Two) showed the fishes remained
together but each female type associated with its own kind. Shade and a
gravel substrate were important habitat parameters.
Specific habitat preferences may not be adaptive due to seasonal
water fluctuations but there are different ecological preferences by each
female type. Associations could account for Phase One laboratory results
and ecological differences. Combined data indicate associations are the
likely mechanism, but habitat preferences are possible. Seasonal factors
and artificial conditions may have caused diverse results.

Embryos of Lucania parva Baird from two sites in the Florida
Keys were raised in four temperature regimes, 18°, 22°, 26°, and 30°C
to determine the response of vertebral numbers to different incubation
temperatures. The result was in inverse linear relationship, with
vertebral numbers increasing with decreasing temperature. Temperature
modified the developmental rates, causing the embryos in the warm
temperatures to hatch earlier than those in the cold temperatures.