Simulated impacts of juvenile mortality on Gulf of Mexico sturgeon populations.
We used an age-structured computer model to assess the impact of changes in juvenile mortality on the Gulf of Mexico sturgeon population in the Suwannee River, Florida. We simulated population trends under four levels of annual juvenile mortality (20, 25, 30, and 35%). As the rate of mortality increased, population size decreased, and rates of population growth shifted from positive to negative. Our models indicated that juvenile survival is important to the success of gulf sturgeon populations, and mortality estimates are needed to predict population viability. We suggest that life history studies in estuaries should be conducted, and bycatch rates for commercial fisheries should be quantified to aid in the management and conservation of gulf sturgeon. (+info)
Identification of the lantibiotic nisin Q, a new natural nisin variant produced by Lactococcus lactis 61-14 isolated from a river in Japan.
Lactococcus lactis 61-14 isolated from river water produced a bacteriocin active against a wide range of Gram-positive bacteria. N-terminal amino acid sequencing, mass spectral analysis of the purified bacteriocin, and genetic analysis using nisin-specific primers showed that the bacteriocin was a new natural nisin variant, termed nisin Q. Nisin Q and nisin A differ in four amino acids in the mature peptide and two in the leader sequence. (+info)
Two distinct phylogenetic clades of infectious hematopoietic necrosis virus overlap within the Columbia River basin.
Infectious hematopoietic necrosis virus (IHNV), an aquatic rhabdovirus, causes a highly lethal disease of salmonid fish in North America. To evaluate the genetic diversity of IHNV from throughout the Columbia River basin, excluding the Hagerman Valley, Idaho, the sequences of a 303 nt region of the glycoprotein gene (mid-G) of 120 virus isolates were determined. Sequence comparisons revealed 30 different sequence types, with a maximum nucleotide diversity of 7.3% (22 mismatches) and an intrapopulational nucleotide diversity of 0.018. This indicates that the genetic diversity of IHNV within the Columbia River basin is 3-fold higher than in Alaska, but 2-fold lower than in the Hagerman Valley, Idaho. Phylogenetic analyses separated the Columbia River basin IHNV isolates into 2 major clades, designated U and M. The 2 clades geographically overlapped within the lower Columbia River basin and in the lower Snake River and tributaries, while the upper Columbia River basin had only U clade and the upper Snake River basin had only M clade virus types. These results suggest that there are co-circulating lineages of IHNV present within specific areas of the Columbia River basin. The epidemiological significance of these findings provided insight into viral traffic patterns exhibited by IHNV in the Columbia River basin, with specific relevance to how the Columbia River basin IHNV types were related to those in the Hagerman Valley. These analyses indicate that there have likely been 2 historical events in which Hagerman Valley IHNV types were introduced and became established in the lower Columbia River basin. However, the data also clearly indicates that the Hagerman Valley is not a continuous source of waterborne virus infecting salmonid stocks downstream. (+info)
Patterns of food resource use by two congeneric species of piranhas (Serrasalmus) on the Upper Parana River floodplain.
Serrasalmus marginatus invaded the Upper Parana River after construction of the Itaipu Dam in November 1982. This was followed by a reduction in abundance of the native species S. spilopleura. Analysis of the pattern of food resource use revealed that both species employ the same feeding strategy, eating mainly fish (whole fish or muscle fragments) and fins bitten off their prey. The diurnal activity period and the feeding rhythm were better-defined in S. marginatus. For young individuals of both species, food was taken in a significantly discontinuous manner (F = 2.83; p < 0.05 and F = 13.25; p < 0.05), with a peak at 4 p.m. Ontogenetic differences in diet, the strong feeding overlap of larger individuals of S. marginatus and smaller individuals of S. spilopleura, and the aggressiveness of S. marginatus in establishing feeding territories may have contributed to the success of the invading species. (+info)
Aquatic macrophytes as feeding site for small fishes in the Rosana Reservoir, Paranapanema River, southeastern Brazil.
In the present investigation we studied the feeding habits of the fishes associated with aquatic macrophytes in the Rosana Reservoir, southeastern Brazil. Twenty fish species were collected during four field trips, regularly distributed across the dry and wet seasons. Focal snorkeling observations of the fishes were made over a total of six hours. Nine species were present in abundances of more than 1% and, therefore, had their feeding habits analyzed. Hemigrammus marginatus, Roeboides paranensis, Hyphessobrycon eques, Astyanax altiparanae, Serrasalmus spilopleura, and Bryconamericus stramineus were predominantly invertivores, with predominance of aquatic insects (Diptera, Ephemeroptera, and Trichoptera immatures) among their food items. The predominantly algivores were Apareiodon affinis, Serrapinnus notomelas, and Satanoperca pappaterra, with high frequency of filamentous blue-green algae, diatoms, clorophyts, and periderm. The different microhabitat exploitation plus diet composition suggests partitioning of resources and absence of food competition among the most representative fish species in the studied community, indicating the importance of the naturalistic approach to fish ecology studies. (+info)
Parotocinclus planicauda, a new species of the subfamily Hypoptopomatinae from southeastern Brazil (Ostariophysi: Loricariidae).
Parotocinclus planicauda, a new species from a tributary of the Doce River drainage in Minas Gerais State, Brazil, is distinguished from all other species of the genus by the presence of a caudal peduncle almost quadrangular in cross section; the anterior position of the adipose fin, close to the dorsal fin insertion; and very small orbits. A key to the Parotocinclus species of eastern Brazilian coastal rivers south of the Sao Francisco River is provided. (+info)
Endoparasite infracommunities of Hemisorubim platyrhynchos (Valenciennes, 1840) (Pisces: Pimelodidae) of the Baia River, Upper Parana River floodplain, Brazil: specific composition and ecological aspects.
Parasites of 136 specimens of Hemisorubim platyrhynchos, popularly called jurupoca, were analyzed. Fourteen parasite species were recorded: four digeneans (Crocodilicola pseudostoma, one Gorgoderidae species, Sanguinicola platyrhynchi, and Sphincterodiplostomum sp.); three cestodes (Goezeella paranaensis, Spatulifer maringaensis, and Mariauxiella piscatorum); five nematodes (Contracaecum Type 1 larvae of Moravec, Kohn, & Fernandes, 1993; Contracaecum Type 2 larvae of Moravec, Kohn, & Fernandes, 1993; Cucullanus (Cucullanus) zungaro; Eustrongylides ignotus; and Goezia sp.); one acanthocephalan (Quadrigyrus machadoi), and one pentastomid (Sebekia sp.). Most of the helminth specimens were found in larval stages, confirming that H. platyrhynchos is a significant source of their transmission. No dominance was reported. With the exception of Contracaecum Type 2 (featuring random dispersion), the species had a clumped pattern of dispersion in the host sample. Evidence of competition among parasite species was not reported. Several species of parasites were correlated with host size and sex. This fact may be explained by increase in food content and possible behavioral modifications of male and female hosts. Infracommunity diversity was not related to host size or sex. (+info)
Carbon sources and trophic position of the main species of fishes of Baia River, Parana River floodplain, Brazil.
In order to verify the carbon source and trophic position of the main species of fishes, of the Parana River floodplain, we analysed the proportion of stable carbon (delta 13C) and nitrogen (delta 15N) isotopes in muscle of fishes sampled in the rainy season. We analyzed adult individuals of Loricariichthys platymetopon, Schizodon borellii, Leporinus lacustris, Auchenipterus osteomystax, Iheringichthys labrosus, Leporinus friderici, and Serrasalmus marginatus. These data were compared with the results obtained by the analyzing stomach contents. The primary producers found in the Baia River were the C3 plants (riparian vegetation, macrophytes, periphyton, and phytoplankton) and the C4 plants (macrophytes). The results of the contribution analysis revealed that the carbon used by the species was derived from C3 plants. According to the trophic position estimates (diet and delta 15N), the species primarily consumed Loricariichthys platymetopon, Schizodon borellii, Leporinus lacustris, and Leporinus friderici and, secondarily Auchenipterus osteomystax, Iheringichthys labrosus, and Serrasalmus marginatus. There was no significant difference between the two methods utilized. (+info)