Quantitative analysis of the microtubule system in isolated fish melanophores

Isolated melanophores of the angelfish, Pterophyllum scalare, have been used in a morphometric analysis and a quantitative study of their microtubule system. Using transverse sections spaced at regular intervals, the changes associated with the process of pigment aggregation have been determined. Upon the concentration of pigment granules in the central cell region, almost half of the cytoplasmic portion is also withdrawn from the peripheral cell regions. Counts of microtubules within a cell sector in cells with pigment aggregated and dispersed, respectively, reveal (a) a constancy of the number of microtubules in this sector regardless of the distance from the cell center, and (b) a reduction of microtubule number in cells with pigment aggregated by about 58%. On the basis of these counts, the total number of microtubules has been calculated. In the dispersed state, about 2,400 microtubules extend between the center and the periphery of the cell, while their number is about 1,000 in the aggregated state. Using a 13-protofilament model of a microtubule and relevant data on size and molecular weight of microtubule subunits, the amount of tubulin present as microtubules is calculated. In the average, the cells contain 1.95·10⁸ monomers corresponding to 1.78·10^?8 mg tubulin. A tentative estimation of the concentration of tubulin inside a melanophore yields values of 6.1 mg/ml for the whole cell and 16.5 mg/ml for the cytoplasm alone (excluding membrane-bound organelles). Based on this estimation, a comparison, with microtubule assembly in vitro is made.     

Induction of fever in a teleost fish (Lepomis gibbosus, L.)

Although fishes are ectotherms they are nevertheless able to thermoregulate behaviorally by selecting appropriate water temperatures (1). In a temperature gradient fish will congregate to a species-specific range of preferred temperature (“final thermal referendum”) which is unaffected by previous thermal history of the individual (2,3). Several aquatic (and terrestrial) ectothermic vertebrates have been found to exhibit “behavioral fever” which is manifested as an increase in preferred temperature above the final thermal preferendum (4). Fever can be elicited by pyrogens: whole bacteria (alive or killed), components of bacterial cellwall (endotoxins), endogenous pyrogens, prostaglandins or from several other sources (5). Since the results with fever induction in fish using whole bacteria or endotoxins are very scarce the aim of the present work was to compare possible thermoregulatory effects of endotoxins and prostaglandins in the same species (Lepomis gibbosus, L.) by means of identical methods.     

Linkage group IV of fish of the genus Xiphophorus (Poeciliidae): Assignment of loci coding for pyruvate kinase-1, glucosephosphate isomerase-1, and isocitrate dehydrogenase-1

Electrophoretic variation ascribable to three enzyme loci, coding for a pyruvate kinase (PK1), a glucose phosphate isomerase (GPI1), and an isocitrate dehydrogenase (IDH1), was observed in three species of fish of the genus Xiphophorus. Electrophoretic patterns in F₁ hybrid heterozygotes confirmed the dimeric structures of GPI and IDH, and indicated a multimeric structure for pyruvate kinase. Variant alleles at the three loci exhibited normal Mendelian segregation in backcross hybrids. Linkage analyses indicate a gene order and estimated recombination of PK1—10%—GPI1—41%—IDH1. No significant interference or sex- or population-specific recombination difference was detected. This group (designated linkage group IV) was shown to assort independently from the nine loci comprising linkage groups I, II, and III and from 23 other informative markers, within the limits of the data. No conclusions with respect to homology of linkage relationships could be reached, due to the presence of presumably duplicated loci in these fish coding for isozymes whose homology with enzymes in other vertebrate species is as yet unestablished.This work was supported in part by Public Health Service Research Grant CA-28909.     

Composition and seasonal fluctuations of the ichthyoplankton community in a shallow tidal channel of Cadiz Bay (S.W. Spain)

The composition and seasonal variation of the ichthyoplankton community in a shallow tidal channel in Cadiz Bay was studied for 5 years (1984 1988), taking fortnightly samples with a conical tide-strained net (0.5 mm mesh). Thirty-nine species belonging to 21 families of teleosts were caught. Four species ( Pomutoschistus microps Kroyer, Atherina hoyeri Risso, Liza rumuda Risso and Lizu a lira Ia Risso) totalled more than 90% of the annual ichthyoplankton abundance. Three species, assumed to be permanent residents, dominated the number offish (837%), and were represented by all their developing stages; 26 species (66.7%) were temporary residents, contributing 17.2% to the total abundance and were represented only by early developing stages; the remaining 10 species were classified as rare. Monthly numbers of species and individuals showed seasonal variation with a main annual peak in spring and in late spring-early summer, respectively. The diversity (H') and evenness (S) indices of this community were low (0.13 to 1.83 and 0.03 to 0.71. respectively), with higher values in winter and late summer, and both were significantly correlated with the log-transformed density of temporary residents (r = 0.43 and 0.41, respectively; P<0.0l) and permanent residents (r=−0.75 and −0.79, respectively; P<0.01). Multivariate classification analysis of samples revealed that similar cyclical changes were taking place in the structure of this ichthyoplankton community every year; three periods could be differentiated: (1) a cool period of low fish density but relatively high diversity; (2) moderate temperature and salinity with high numbers of species and density but low diversity and (3) a warm period of moderate diversity and fish density.     

Edward Smith Deevey 1914–1988

Stone loach and bullhead were given a choice of Chironomus and Asellus prey in experiments using solitary fish and fish in company. Solitary fish ate more than fish in company. The effect of light and substratum type on feeding was investigated. Both species ate more prey items on gravel than silt when a significant difference was observed. Bullhead ate more than loach in the light on both substrata. The only experiment in which loach ate more than bullhead was on a silt substratum in the dark. It is concluded that these two species utilise different components of the available food resources in chalk streams by adopting different habitats.     

Salinity tolerances of four species of fish from the Murray-Darling River system

The salinity tolerances of four species of small fishes native to the Murray-Darling river system were measured. Slow acclimation LD₅₀s were 43.7 ± 1.7 g L⁻¹ for Craterocephalus stercusmuscarum Gunther, 38.0 ± 1.1 g L⁻¹ for Hypseleotris klunzingeri (Ogilby), 58.7 ± 0.9 g L⁻¹ for Retropinna semoni (Weber), and 29.8 ± 0.7 g L⁻¹ for Melanotaenia splendida (Castelnau). The salinity tolerance of M. splendida was also measured by direct transfer, providing an estimated LD₅₀ (infinite exposure time) of 20.8 g L⁻¹, ∼ 70% of the slow acclimation value. Results suggest that at least adults of the species studied are under no threat from present or foreseeable salinities in the Murray River.     

Impact of fishery management on Cladoceran populations

Zooplankton of the fish pond reveals a two-year periodicity, which is induced by the two-year cycle of fishery management. In the first year of each cycle, the biomass of large cladocerans prevailed — mainly adult specimens of the species Daphnia pulicaria Forbes, which were absent in the second year. The species Daphnia galeata Sars was present in both years, however, it is more numerous in the second year. The fraction of small zooplankton (rotifers, nauplii, Bosmina, newborn Daphnia) was abundant in the second years, but scarce in the first years, respectively.     

High Expression of the HNK-1/L2 Carbohydrate Epitope in the Major Glycoproteins of Shark Myelin

The major 24- and 28-kDa glycoproteins in shark PNS and CNS myelin express high levels of the adhesion-associated HNK-1/L2 carbohydrate epitope. The 28-kDa protein, but not the 24-kDa protein, cross-reacts strongly with one of two anti-bovine P0 antisera not previously tested against fish myelin proteins. Shark PNS and CNS myelin also contains smaller amounts of high-molecular-weight HNK-1-positive proteins, including a prominent broad band in the 65-85-kDa range. Although myelin-associated glycoprotein (MAG) is well known to react with HNK-1 in some mammals, monoclonal and polyclonal anti-MAG antibodies did not react with the high-molecular-weight HNK-1-positive material in shark myelin, a result suggesting that it is not a MAG-like protein. The high expression of the HNK-1/L2 epitope in glycoproteins of shark myelin, including the major P0-related ones, suggests that this adhesion-related carbohydrate structure may have had an important role in the molecular evolution of the myelinating process.     

草鱼血液学的研究：Ⅱ.血清电解质和尿素氮的周年变化

本文研究了草鱼稚鱼血清钾、钠、钙、氯、无机磷和尿素氮含量的周年变动规律,分析了水温、体重对上述血液化学成分的影响。结果显示其周年变动无一定规律性可循。血清钠、氯变动辐度较小,无机磷和尿素氮变动幅度较大,幅值约有4倍。水温与血清钾显示正相关(P≤0.05),与钠、钙显示负相关(P≤0.01,P≤0.05)。血清钠、尿素氮有随体重增加含量增高的趋势,而钾却显著减少。     

Effects of paper mill effluents on the fish fauna of stony shores of Lake Päijänne

The fish fauna of the stony littoral in the central parts of L. Päijänne was studied by electric fishing on four occasions during 1988–1989. Ten fish species and 1681 individuals (14.5 kg) were caught in the 15 fishing sites (4096 m²) which gives a mean density of 0.41 ind. m^–2 and biomass of 3.5 gm^–2. Effluent from two large paper mills causes a clear zonation of the fish fauna in the area. In the most polluted shores, only burbot and perch occurred regularly and the reproduction of other species was inhibited. In the semipolluted area (5–15 km from the Kaipola paper mill), burbot and stone loach occurred regularly, but owing to low numbers of perch and bullhead the total densities were usually low.The clean shores were characterized by an abundance of stone loach and bullhead and locally also of minnow, which seemed to be very sensitive to pollution. The strong floods during summer 1988 had positive effects on the reproduction of perch and pike, but the densities of other species were highest during the normal water level in autumn 1989.