An experimental study of factors affecting the distribution of yellow perch and central mudminnows along a species richness gradient

Synopsis Effects of environmental factors on the distribution and abundance of yellow perch and central mudminnows in northern Wisconsin were examined by holding populations of these fishes within single-species enclosures in a series of three small forest lakes having a species-richness gradient of one to four species. These enclosures allowed each species to experience environmental conditions within each lake without directly interacting with each other. In the four-species lake, two other sets of enclosures addressed the effects of intra- and interspecific competition. Changes in total biomass of enclosure stocks (from growth and mortality) indicated that in the absence of other species, perch did best in the lake containing the richest fish assemblage, intermediate in the two-species lake, and worst in the mudminnow-only lake. Mudminnow stocks similarly performed significantly better in the four-species lake than the mudminnow-only lake. These results suggest that the lakes' environmental conditions contribute to the patterns of presence and abundance of perch, but that interspecific interactions override a similar contribution for the mudminnow, which is regarded as a fugitive species. Perch performances were also sensitive to fish densities within enclosures, declining significantly when stocks were doubled, either by adding more perch or equal numbers of mudminnows.     

Fine structure and motility of spermatozoa and composition of the seminal plasma in the perch

The fine structure and motility of spermatozoa and the composition of the seminal plasma of the perch Perca fluviatilis are investigated by electron microscopy, computer assisted cell motility analysis (CMA) and biochemical methods. The spermatozoon is asymmetrical as the flagellum inserts mediolateral on the nucleus. It lacks an acrosome, has an ovoid head and a small midpiece with one mitochondrion. Sperm motility–initiated in distilled water (10° C)–is characterized as follows: 85·0 ± 2·7% of the spermatozoa are motile, the main swimming type (10 ± 1 s after motility initiation) is the linear motion (61·4 ± 24·4%) and the average swimming velocity is 122·4 ± 21·9 μm s^–1. When motility is initiated with NaCl, glucose or sucrose solutions of 100 mosmol kg^–1 the percentage of motile spermatozoa and the swimming types are similar as in water, but the swimming velocity (174·0 ± 22·3 μm s^–1) is significantly higher. Motility is inhibited by high osmolality of the diluent: when increasing the osmolality of the saline solutions to 350 mosmol kg^–1 sperm motility is totally suppressed while potassium (10–40 mmol 1^–1) does not affect motility parameters. pH optimum for sperm motility is between pH 7·0 and 8·5. The seminal fluid contains 124·01 ± 21·68 mmol 1^–1 sodium, 10·22 ± 1·11 mmol 1^–1 potassium and 0·72 ± 0·26 mmol 1^–1 calcium. pH is 8·25 ± 0·09, and osmolality 283·90 ± 37·19 mosmol kg^–1. The following organic components were determined: monosaccharides (glucose 63 ± 19 μmol 1^–1, fructose 54 ± 28 μmol 1^–1, galactose 59 ± 25 μmol 1^–1), lipids (cholesterol 5·51 ± 6·42 μmol 1^–1, triglycerides 72 ± l00 μmol l^–1, cholesteryloleate 15–150 μmol 1^–1, phosphatidylcholine 26 · 31 μmol 1^–1, glycolipids 1–10 mg 100 m1^–1), lactate 108 ± 99 μmol 1^–1, hydroxybutyrate 102 ± 99 nmol 1^–1, choline 59 ± 159 μmol 1^–1, protein 344·75 ± 59·06 mg 100m1^–1, enzymes (β-d -glucuronidase l.4 ± 0.7 μmol h^–1 100 ml^–1, protease (caseolytic activity) 1·0 ± 0·6 μmol h^–1 100 ml^–1, alkaline phosphatase 2520·0 ± 861·0 μmol h^–1 100 ml^–1, acid phosphatase 44.0 ± 16.0 μmol h^–1 100 ml^–1, glucose-6-phosphate dehydrogenase 38·9 ± 86·9 μmol h^–1 100 ml^–1, lactate dehydrogenase 134·4 ± 69·6 μmol h^–1 100 ml^–1, butyrylcholine esterase 0·014 ± 0·010 μmol h^–1 100 ml^–1, adenosine triphosphatase 562·8 ± 665·4 μmol h ^–1 100 ml^–1).     

Electron microscopic and histochemical investigations of the atretic oocyte of Perca fluviatilis L. (Teleostei)

Summary The regression of atretic oocytes in Perca fluviatilis was studied by histochemical, light and electron microscopic methods. The course of regression can be divided into three stages, the first two comprising the dissolution of the atretic oocyte and its phagocytosis by the granulosa cells of the follicular epithelium, and the third stage consisting of the dissolution of the granulosa cells themselves. The ultrastructure in all three stages shows only features related to phagocytosis and lysosome formation. In particular, there is no agranular endoplasmic reticulum formed within the phagocytically active granulosa cells, nor is there any 3-hydroxysteroid dehydrogenase activity (3-HSD). Large yellow-orange pigments, formed during the third stage of regression, are ascribed to a relative deficiency of lysosomes in lipid digestion, and do not result from a preceeding steroid-synthesising phase as in mammalian corpora lutea. Thus, the atretic oocyte of P. fluviatilis is considered not to give rise to a corpus luteum formation with endocrine function, but merely represents a degenerative structure.     

Ontogenetic changes in behavioural and histological measures of visual acuity in three species of fish

Synopsis Vision plays an important role in the early life history of fishes. We investigated the ontogenetic changes in visual acuity of early life history stages of alewife,Alosa pseudoharengus, yellow perch,Perca flavescens and bloater,Coregonus hoyi, across a range of sizes. Acuities were determined through histological examination of the retinae of larvae. Reactive distances of larvae to prey were estimated through videophotography of their response to prey and were then converted to measurements of visual angle. Both measures of visual ability improved with size (age) for all species. When behavioural and anatomical measures of ability were compared as a function of size, the data indicate that fish are anatomically more capable of seeing objects than the behavioural response suggests. In two of the three species, the relationship between histological acuity and visual angle was not constant. These results may indicate that while vision may limit initial rates of encounter and feeding, increases in visual acuity mean that in older stages limitations on encounter and feeding are more likely to be behavioural. Furthermore, these results indicate that encounter rates based upon histological estimates of visual acuity will be greater than comparable estimates based upon reactive distances. We recommend calculation of encounter rates based upon reactive distances. Present address: Department of Biology, McGill University, 1205 Ave, Dr. Penfield, Montreal, PQ H3A 1B1, Canada     

The vascular and epithelial serotonergic innervation of the actinopterygian gill filament with special reference to the trout,Salmo gairdneri

Summary Antibodies against serotonin and 5-methoxytryptamine reveal indolaminergic neurons innervating the proximal part of the efferent arterial vasculature, the filament epithelia, the central venous sinus, and certain other serotonergic cells of the teleost gill filament. In the same area, acetylcholinesterase-positive and indoleaminergic neurons have already been described. We propose that these populations of neurons belong to a single neuronal type but express different agents. Our current results support this idea; in particular, they point to the presence of a single type of serotonin-containing nerve terminal, impinging on vascular smooth muscle. These results are in agreement with physiological data showing (i) the existence of non-cholinergic (atropine-resistant) vasoconstriction of the gill vasculature after nerve stimulation, and (ii) a potent vasoconstrictory action of infused serotonin. In addition, the above-mentioned serotonergic neurons have synaptic contacts with catecholaminergic nerve fibers, suggesting the existence of a modulatory relationship between the sympathetic and the cranial autonomic nerves supplying the teleost gill. Finally, these neurons show morphological relationships with a previously undescribed type of branchialserotonergic cell. The role of the parasympathetic nerve plexus of the teleost gill filament in the control of respiration and ionoregulation is discussed.     

Physiological correlates of growth and condition in the yellow perch (Perca flavescens)

This study on yellow perch (Perca flavescens) examines a series of enzymatic markers and the relative weights of pyloric caeca and visceral lipids, their response to changes in feeding regime and their potential use to infer recent changes in growth rate and fish condition. Fish were exposed to four different feeding regimes for 12 weeks resulting in specific growth rates ranging from 0.3% to 3.5% (%/day). Growth and condition responded rapidly to changes in ration and the weight of pyloric caeca and visceral lipids reflected increased feed intake. Growth rate was correlated with muscle citrate synthase and caecal nucleoside-diphosphate kinase activities, whereas condition was correlated with muscle citrate synthase and lactate dehydrogenase activities and with caecal glucose-6-phosphate dehydrogenase activity. Results showed that enzyme activities and biometric parameters responded rapidly to increased feed intake, but the response was slower when food intake decreased. Plateaus were attained for both condition and visceral lipid index, but the relative weight of pyloric caeca continued to increase throughout the experimental period. Results from this study could, in principle, be used to infer recent growth and energy status in wild yellow perch and thus provide an indicator of food availability in their environment.     

Quantifying the activity and movement of perch in a temperate lake by integrating acoustic telemetry and a geographic information system

The horizontal movement patterns of perch (Perca fluviatilis L.) were studied by means of an automatic positioning system in a small Mediterranean temperate lake in northeastern Spain. Seven perch (247–265 mm in fork length, 243–271 g in weight) were implanted surgically with ultrasonic transmitters (38 mm long, 3.5 g in water) and their positions monitored approximately every 180 s using a radio-linked acoustic positioning (VRAP) system. Fish positions were integrated into a geographic information system database with information on date, time, slope and bottom depth. As a measure of the intensity of movement, the swimming speed was calculated. The Minimum Convex Polygon area was obtained as a measure of the area of activity. The data dispersion was calculated as r ² (the mean squared distance from the center of activity). The tagged perch showed individual variations in activity levels, but all had a circadian pattern, being less active at night (average speed 6.0 cm s^–1) than during the day (average speed 10.4 cm s^–1). They exhibited two peaks of activity, at sunrise and sunset. Two patterns of movement emerged, the first characterised by movement between the limnetic and the littoral zones, the second restricted to the shoreline. Fish appeared to follow the same path, reducing the area of activity to a limited part of the lake. Also, fish returned to the same place after movements, showing site fidelity but only for a few days. Overall, although perch could be very abundant in open waters (limnetic zone), they demonstrated a high dependence on the littoral zone.     

Influences of multilocus heterozygosity on size during early life

Genetic diversity has been hypothesized to promote fitness of individuals and populations, but few studies have examined how genetic diversity varies with ontogeny. We examined patterns in population and individual genetic diversity and the effect of genetic diversity on individual fitness among life stages (adults and juveniles) and populations of captive yellow perch (Perca flavescens) stocked into two ponds and allowed to spawn naturally. Significant genetic structure developed between adults and offspring in a single generation, even as heterozygosity and allelic richness remained relatively constant. Heterozygosity had no effect on adult growth or survival, but was significantly and consistently positively related to offspring length throughout the first year of life in one pond but not the other. The largest individuals in the pond exhibiting this positive relationship were more outbred than averaged size individuals and also more closely related to one another than they were to average‐sized individuals, suggesting potential heritability of body size or spawn timing effects. These results indicate that the influence of heterozygosity may be mediated through an interaction, likely viability selection, between ontogeny and environment that is most important during early life. In addition, populations may experience significant genetic change within a single generation in captive environments, even when allowed to reproduce naturally. Accounting for the dynamic influences of genetic diversity on early life fitness could lead to improved understanding of recruitment and population dynamics in both wild and captive populations.     

Competition for minerals between Acanthocephalus lucii and its definitive host perch (Perca fluviatilis)

Concentrations of various essential and toxic elements (Ba, Ca, Co, Cu, Fe, Mg, Mn, Sr, Zn and Al, Ag, Cd, Cr, Ni, Pb, Tl) were analysed by inductively coupled plasma mass spectrometry in the acanthocephalan Acanthocephalus lucii and in different tissues of its host Perca fluviatilis. Nearly all the elements were found in significantly higher concentrations in the acanthocephalan than in the host tissues. Spearman correlation analysis revealed several strong inter-element associations within the organs of perch and within the parasites. Furthermore, statistical analysis revealed different competitive interactions. The concentrations of several essential elements (Ba, Ca, Fe, Mn, Sr and Zn) within the parasites decreased with an increasing number or weight of worms inside the intestine of the host. Additionally, the levels of some elements in the perch liver were negatively correlated with the weight of A. lucii in the intestine. Thus, it emerged that not only is there competition for essential elements between acanthocephalans inside the gut but there is also competition for these elements between the host and its parasites.     

Resistance of perch eggs to attack by aquatic fungi

In the distinctive gelatinous Perca fluviatilis egg mass, limited fungal growth by Aphanomyces and Saprolegnia spp. especially S. diclina , occurred within dead eggs but did not spread to adjacent live eggs. Perch eggs exposed to parasitic challenge by Saprolegnia parasitica , S. dieclina (type III) and S. ferax , under fluctuating temperature regimes replicating spring water temperatures, did not have significantly greater mortality than did unchallenged controls. The observations suggest that perch eggs have some anti-fungal properties which usually prevent the spread of fungus throughout the egg mass and that under normal spring temperatures there should be negligible ecological consequences of fungal infection in perch egg masses.