Genetic variation in Lake Erie yellow perch (Percaflavescem) demonstrated by mitochondrial DNA analysis

Restriction fragment length polymorphism analysis of yellow perch ( Perca flavescens ) mitochondrial DNA from a Lake Erie population revealed seven variants in 22 fish (nucleon diversity 0.481). These fish were collected from an area where previous studies using allozymes had failed to reveal any genetic variation.     

Variation in flexural stiffness of the lepidotrichia within and among the soft fins of yellow perch under different preservation techniques

Although the ray‐finned fishes are named for their bony, segmented lepidotrichia (fin rays), we are only beginning to understand the morphological and functional diversity of this key vertebrate structure. Fin rays support the fin web, and their material properties help define the function of the entire fin. Many earlier studies of fin ray morphology and function have focused on isolated rays, or on rays from only one or two fins. At the same time, relatively little is known about how different preservation techniques affect the material properties of many vertebrate structures, including fin rays. Here, we use three‐point bending tests to examine intra‐ and inter‐fin variation in the flexural stiffness of fin rays from yellow perch, Perca flavescens. We sampled fin rays from individuals that were assigned to one of three preservation treatments: fresh, frozen, and preserved with formalin. The flexural stiffness of the fin rays varied within and among fins. Pelvic‐fin rays were the stiffest, and pectoral fin rays the least stiff. The fin rays of the dorsal, anal, and caudal fins all had similar stiffness values, which were intermediate relative to those from the paired fins. The flexural stiffness of the fin rays was higher in rays that were at the leading edge of the fin. This variation in flexural stiffness was associated with variation in joint density and the relative length of the unsegmented proximal base of the fin rays. There was no significant difference in flexural stiffness between fresh and frozen specimens. In specimens preserved with formalin, there is a small but significant effect on stiffness in smaller fin rays.     

Fluidized-bed drying and storage stability of Cryptococcus flavescens OH 182.9, a biocontrol agent of Fusarium head blight

A method to produce dried granules of Cryptococcus flavescens (formerly Cryptococcus nodaensis) OH 182.9 was developed and the granules evaluated for storage stability. Small spherical granules were produced and dried using a fluidized-bed dryer. A drying and survival curve was produced for the process of fluidized-bed drying at 30°C. The granules were dried to different moisture contents (4, 7, 9 and 12%) and evaluated for storage stability at 4°C for up to a year. These different moisture contents granules had the following respective water activities (0.22, 0.38, 0.47 and 0.57 a _w). The results show the storage stability varied significantly across this moisture content range. The 9% moisture content sample had the best short-term stability (up to 4 months), while 4% moisture content had the best long-term survival (1 year). A desorption isotherm of C. flavescens was determined and modeled. The results of the storage stability and drying studies are interpreted in context of the desorption isotherm.     

Diet of lactating South American sea lions,as inferred from stable isotopes,influences pup growth

Serum and blood cell δ¹³C and δ¹⁵N signals from 26 suckling pups of the South American sea lion from northern Patagonia were used as proxies of the composition of their mothers' diet to test the hypothesis that the foraging habits of the mother influence pup growth. Samples of primary producers and the female potential prey were analyzed to establish baseline isotopic values and to determine energy density. Pups were weighed to determine specific growth rate. Individual variability in female diet was large, probably as a consequence of dissimilarities in the foraging performance that depends on the individual's age, body size, and/or foraging skills. Growth of a pup was influenced by its mother's diet, as pups of females mostly relying on pelagic offshore prey were found to grow faster than those of females basing their diet on benthic coastal prey.     

Comparison of response distance to prey via the lateral line in the ruffe and yellow perch

The ruffe Gymnocephalus cernuus and the yellow perch Perca flavescens (both Percidae), have very different cephalic lateral line systems. The ruffe, which is nocturnal and frequents turbid water, has a cephalic lateral line with very wide canals, large neuromasts, and membranes covering the canal openings. This anatomy is convergent with that of many deep-sea fishes. The yellow perch has a lateral line composed of neuromasts enclosed in narrow canals freely open to the water. This anatomy is typical of active, diurnal, shallow-water fishes. Laboratory experiments in the dark using infra-red video equipment revealed that the ruffe detects Daphnia magna (Crustacea: Daphnidae) and the mayfly Hexagenia limbata (Insecta: Ephemeridae) at a greater distance than the yellow perch and that it also swims faster whilst searching for prey. The swimming of the ruffe consists of a thrust by the pectoral and caudal fins, followed by a glide, the prey being detected during the glide. It is suggested that the membranes over the openings in the ruffe's lateral line function to eliminate self-generated laminar flow 'noise' from reaching the neuromasts.     

Ecdysteroid production during caste differentiation in larvae of the ant, Plagiolepis pygmaea

ABSTRACT. Variations in ecdysteroids were measured by radio-immunoassay in worker-biased and queen-biased larvae of the ant Plagiolepis pygmaea Latr. (Hymenoptera, Formicidae) during late larval development, i.e. from the end of winter diapause up to the prepupal period. At the end of diapause, larvae are bipotential and, depending on culture conditions, can become either queens or workers. Ecdysteroid profiles revealed that there are striking differences between the two castes: worker larvae showed high titres during their development, queen larvae had low titres over the same period.