Relative weight (Wr) of yellow perch (Perca flavescens) was evaluated for fish collected from the Indiana waters of Lake Michigan in June, July and August of 1976 and 1984-1991. Computation of Wr was completed for individual fish in 20 mm intervals over the size range from 100-219 mm using Wr = (W/Ws) 100 where W=weight of a fish in grams and Ws=standard weight for a fish of the same length. Length was highly correlated with weight in all years for males, females and sexes combined (r=0.97-0.99). Distributions of predicted weights for fish at 130 mm and 250 mm were at or near modes of the populations used to construct the Ws equation for yellow perch. Relative weights consistently decreased with increasing size in all years for males, females and sexes combined. Using 1976 length-weight data when the yellow perch population was sparse and fast growing as a standard (100%) for comparison, relative condition factors (Q) increased with increasing size in some years and decreased with increasing size in others for males females and sexes combined and it did not appear to be length dependent. When comparing Wr at 100 mm and 200 mm by sex and month, f hales had higher Wr than males at 100 mm in seven of nine years in June, six of nine years in July and only four of nine years in August. Female fish also had higher Wr than males at 200 mm in eight of nine years in June and July and six of nine years in August. There appeared to be no consistent pattern or trend of Wr increasing or decreasing by month for males, females or sexes combined. When Kn was evaluated for 100 mm and 200 mm fish by sex and year, male fish had higher Kn than females at 100 mm in all eight years. Male and female fish at 200 mm were more similar; male fish had higher Kn in three years, lower Kn in three years and equal Kn in two years. No relationships were found at 200 mm comparing Wr or Kn and CPE (quality/ h) for males (r=0.43; r=0.42), females (r=0.12; r=0.13) or sexes combined (r=0.28; r=0.22). Simple linear correlations of proportional stock density (PSD) with Wr and Kn revealed relative weights increased with PSD for 100 mm (r=0.51) and 200 mm (r=0.72) fish. Relative condition factors also increased with PSD for 100 mm fish, however the relationship was weak (r=0.30) but a strong correlation was found between Kn and PSD (r=0.81) for 200 mm fish. Based on these results, it appears that either Kn or Wr may be used inassessing the condition of yellow perch from the Indiana waters of Lake Michigan. / Department of Biology

Coastal populations of perch (Perca fluviatilis) in the Baltic Sea has declined substantially the last decades while the populations of three-spined sticklebacks (Gasterosteus aculeatus) has increased rapidly during the same time period. Earlier studies have suggested that predation on perch larvae and or competition from sticklebacks are the causes behind the decline in perch. To test if predation from sticklebacks commonly occur on perch larvae as well as provide data on stickleback diets in general, diets of sticklebacks were examined by looking at the stomach content of collected samples of sticklebacks from different bays along the Swedish and Finnish coast. Results showed no evidence of stickleback predation on perch larvae as no perch larvae were found in any of the examined stomachs.  Three-spined sticklebacks generally had the same diet in all studied bays consisting mainly of Chironomidae and Asellus aquaticus. The diet results suggest that competition between perch larvae and sticklebacks is minor if any due to low proportions of zooplankton found in the stomachs of the sticklebacks while zooplankton is the main food source for perch larvae. In bays where three spined sticklebacks were found with nine-spined sticklebacks they generally had similar diets. Still, due to a larger size and gape size of three-spined sticklebacks they fed more on larger prey like Asellus aquaticus while nine-spined sticklebacks contained smaller prey such as benthic cladocerans. Due to few samples from bays where sticklebacks were found together with perch larvae, no conclusion regarding predation on larvae as the main the mechanism for declines in coastal perch population can be drawn from the results in this study.

by Chiu Shui-fan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1989. / Bibliography: leaves 186-203.

This thesis presents an implementation of autonomous indoor perching using only onboard sensors on a low-cost, custom-built quadrotor. The perching aggressive maneuver is representative of a class of control problems for aerobatics that requires an agile and robust control system for maneuvering accurately at high speeds. Such research extends the typical functionality of micro air vehicles (MAV) from low speed and stationary observation to dynamic aerobatic transitions for broader operational capabilities including confined landings and evasive maneuvering. To achieve this, three major challenges are overcome: precise and real-time positioning, sensing of the perch and path to the perch, and control methods for robust and accurate tracking at high speeds. Navigation in unstructured, global positioning system (GPS)-denied environments is achieved using a visual Simultaneous Localization and Mapping (SLAM) algorithm that relies on an onboard monocular camera. A secondary camera, capable of detecting infrared light sources, is used to locate the pathway for the maneuver and the perch, simulating sensing of the actual perch, for perching without prior knowledge of the location of the perch. The full physical system architecture is covered in detail, indicating the components and integration necessary to obtain effective aggressive control of an inexpensive quadrotor. The difficulties of attitude stabilization on noisy and lower-quality sensors are successfully addressed so that the air vehicle can be treated as a simple second-order system for the purposes of navigation and response to dynamic maneuvering commands. The system utilizes nested controllers for attitude stabilization, vision-based navigation, and perching guidance, with the navigation controller implemented using novel nonlinear saturation control within a Proportional-Integral-Derivative (PID) structure. The quadrotor is therefore able to autonomously sense the perch, reach initial high speeds for obtaining rapid deceleration from aerodynamic effects, dynamically transition to a high angle of attack post-stall configuration, and make a low-speed accurate landing on an inclined surface, using only onboard sensors.

Two decades ago the recruitment of YOY perch (Perca fluviatilis) started to decline along the Swedish east cost of the Baltic Sea. Factors that influence recruitment are e.g. eutrophication that causes habitat losses and overfishing of cod (Gadus morhua) which causes cascading effects in the food web. Filamentous cyanobacterial blooms are often toxic and has increased in the Baltic Sea and its coastal waters. The aim of this field study was to evaluate the effects of salinity and cyanobacterial exposure on fitness related parameters of young of the year (YOY) perch (Perca Fluviatilis) in a natural environment. Our study was performed in the Curonian Lagoon (Lithuania) in August 2009. The lagoon offers a temporary salinity gradient (wind induced influxes from the Baltic Sea) ranging from 7 psu in the north to 0 psu in the south. Submerged enclosures containing YOY perch were set up at three different locations along the salinity gradient in the Lagoon (referred to as North, Middle, South). The duration of the experiment was 21 or 27 days, depending on treatment. Measurements of perch condition were specific growth rate, somatic condition index (SCI) and whole fish lipid and protein content. Average chl a values for the three stations during the experimental time were: north 180 ± 70 µg/l chl a, middle 133 ± 36 µg/l chl a and south 180 ± 52 µg/l chl a. The North and the Middle stations experienced two different salinity influxes reaching a maximum salinity of 6.5 psu at the northern station. The duration of each saline influx was approximately 4-6 days. The saline water did not reach the Southern station at any time. Results show that perch from the southern station were in best condition in terms of specific growth rate and contents of total lipids. Compared to the South the perch condition declined to the Middle station and was lowest at the Northern station which experienced the highest degree of fluctuation in terms of salinity and cyanobacterial exposure. Examination of the abundance of the main food resource at the different stations revealed no statistical differences, which suggest that availability of food was not a factor in explaining the differences in growth.  The results possibly indicate that a changing environment with the potential synergistic negative effects of salinity and cyanobacteria has a higher negative impact on YOY perch condition compared to constantly high concentrations of cyanobacteria.

Phenotypic plasticity is defined as an organism’s ability to express differentphenotypes depending on the environment. Predation is one of the key forces inecology and can indirectly cause a change of the phenotype in fish populations.Pigmentation change in order to match the background is one type of camouflage usedin fish and other organisms. Moreover, pigmentation might depend on environmentalconditions such as turbidity and water colour that affect the light spectrum and thusthe visibility in the water. The phenotypic variation in body pigmentation of perch(Perca fluviatilis L.) has rarely been studied to this date. In this study, I examined ifbody pigmentation of perch varied between different environments and betweenstructurally different habitats (littoral/pelagic). I tested long-term (phenotypicplasticity) and short-term (physiological-behavioural) changes in pigmentation byusing long-term pre-treatments and short-term aquarium experiments. Differences instructurally-diverse habitats were investigated in an extensive field study.Furthermore, experimental results were compared to data from the field. The resultsshow that pigmentation is determined by environmental factors, such as water colouror turbidity, and by structural complexity. Since fishes adapted their pigmentation totheir visual environment, pigmentation is likely used as predator avoidancemechanism in perch. Moreover, it was demonstrated that the environmentally-inducedpigmentation pattern determines the magnitude of short-term pigmentation in perch.

Hybridstreifenbarsche (HSB) sind wertvolle Speisefische, die als aussichtsreiche Objekte der Aquakultur weltweit im Fokus stehen. Eine breite Einführung der Fische in der deutschen Aquakultur bedarf aber einer von Importen unabhängigen Satzfischversorgung. Ziel des Projekts war es, HSB aus F1-Gebrauchshybriden zu vermehren. In mehreren Fällen gelang eine Bruterzeugung, ohne dass jedoch die Rahmenbedingungen fixiert werden konnten, die eine sichere und reproduzierbare Brutgewinnung ermöglichen würde. HSB werden sich deshalb nicht in großem Stil in der sächsischen Aquakultur etablieren. Von einer Gefährdung einheimischer Fischarten ist wegen der offensichtlich überwiegenden, wenn auch nicht vollständigen Sterilität der Hybriden nicht auszugehen.

The aim of this study was investigate if increasing total organic carbon (TOC) affects the growth rate and biomass of perch (Perca fluviatilis) and biomass of roach (Rutilus rutilus). The ongoing climate change affects the climate by increasing annual mean temperature and precipitation. The runoff to surface waters will increase, which also has the consequence that the export of terrestrial organic matter (TOM) and nutrients to surface waters will increase. Increasing of TOM into the surface waters make it darker, i.e. brownification of the water. This brownification of surface water affects the amount of available light for benthic algae causing the benthic primary production to decrease. As the benthic primary production decreases also whole lake ecosystem productivity decreases. The impact on fish biomass and production of fish were studied in five small lakes in Sweden. Lake morphology, water chemistry and fish community characteristics were sampled. A subset of perch from the catch was selected to determine age and growth. Data from age determination was then used to calculate the size dependent growth and production of perch in each lake. Total fish biomass and biomass of perch and roach was negatively affected by TOC and yearly biomass production of perch was lower in lakes with higher TOC. Thus, climate change may at least in small forest lakes lead to lower production and biomass of fish in the future.

Age, growth, and abundance data were collected on yellow perch, Perca fla vescen, in Indiana waters of Lake Michigan in 1987 and 1988. The data collected were compared to data on yellow perch in Indiana waters of Lake Michigan dating back to 1975.Changes in growth, mortality, and abundance between 1975 and 1988 were clearly illustrated by the data. Growth has decreased; back-calculation indicates that "quality" (> 200 mm) perch in 1975 were about age II, however, "quality" perch in 1988 were over age V. Annual mortality values produced from following a cohort or comparing age classes indicate that mortality has decreased since 1981, most sharply in 1987 and 1988. Changes in growth and mortality are likely resultant of large changes in abundance. Indices of abundance (biomass and catch-per-uniteffort) reveal that the yellow perch population has become much more dense in the late 1980's than the 1970's and early 1980's. The percentage of quality perch has decreased, however, the abundance of quality perch has increased and peaked in 1988. / Department of Biology

The relationship between yellow perch Perca flavescens abundance and growth rates were evaluated in the Indiana waters of Lake Michigan from 1984 to 2004. Relative abundance values were taken from trawl catch per unit effort (CPUE), while growth rates were determined by back-calculation. Abundance CPUE during the mid 1980's, was approximately one order of magnitude higher when compared to the 1990 to 2004 period. Growth rates were inversely related to relative abundance and were sexually dimorphic, with females growing faster than males. Regression analysis indicated approximately half of this observed variation in growth was due to abundance, and was most apparent with the smaller and younger fish. Both intraspecific competition and physiological changes associated with maturity are plausible explanations for the relationship. / Department of Biology