The fish heart as a model system for the study of myoglobin

A model is presented for myoglobin study based upon naturally occurring differences in myocardial myoglobin content in fish. The sea raven (Hemitripterus americanus) and the ocean pout (Macrozoarces americanus) have heart myoglobin contents of approx. 65 and 5 nmol/g wet wt, respectively. The maximal activities of enzymes associated with energy metabolism are similar in the two hearts. Isolated perfused hearts performed with similar efficiencies based upon similar rates of work, oxygen consumption and lactate production. Under normoxic perfusion conditions both hearts met 98% of the ATP demand by oxidative mechanisms. Myoglobin-rich sea raven hearts performed significantly better than myoglobin-poor ocean pout hearts under conditions of hypoxia and glycolytic blockage. The performance of sea raven hearts was impaired during hypoxia by decreasing the content of functional myoglobin with hydroxylamine. No effect upon performance was observed with the ocean pout heart. The data provide the first evidence that myoglobin plays a role in the maintenance of contractility in heart under hypoxic conditions.     

The suitability of the free-living nematode Panagrellus redivivus as live food for first-feeding fish larvae

The free‐living nematode Panagrellus redivivus has been recommended as a suitable food source for first‐feeding fish. A new technology for mass production of P. redivivus enables fish hatchery operators to rely on an inexpensive, standardized and permanently available live food for first‐feeding fish larvae. The proximate composition, and the fatty acid and amino acid profiles of nematodes mass produced on oat‐based and purified ingredient media were determined. The quality of nematodes was significantly influenced by the culture medium used. The lipid content and fatty acid composition of nematodes could be modified by using lipid‐enriched media. Mass‐produced nematodes were tested on first‐feeding common carp (Cyprinus carpio L.) and whitefish (Coregonus lavaretus) larvae. Carp larvae, grown on nematodes cultured on oat medium enriched with sunflower oil, showed a higher survival rate (87.1%) than the control group fed frozen zooplankton (82.9%) at the end of the 1‐week feeding experiment. Differences in larval mass between the treatments disappeared after subsequent feeding of a dry diet for 2 weeks. Whitefish larvae can be reared exclusively on a dry diet; here, the initial feeding of nematodes had no effect on final biomass and survival of larvae.     

Larvae of Contracaecum sp. among inshore fish species of southwestern Australia

Larval nematode infections were investigated in 236 fish from 17 estuarine and near-shore species in southwestern Australia. Larvae of the genus Contracaecum were found in 4 species of fish (Acanthopagrus butcheri, Sillaginodes punctata, Mugil cephalus and Aldrichetta forsteri). The prevalence and intensity of infection was highest in the 2 species of mullet: 81% infected and 9.8 +/- 1.5 larvae fish(-1) for M. cephalus; 100% and 12.7 +/- 3.7 larvae fish(-1) for A. forsteri. There was no evidence of post-mortem migration of worms from the visceral organs to the musculature of the fish.     

Host species as a strong determinant of the intestinal microbiota of fish larvae

We investigated the influence of host species on intestinal microbiota by comparing the gut bacterial community structure of four cohabitating freshwater fish larvae, silver carp, grass carp, bighead carp, and blunt snout bream, using denaturing gradient gel electrophoresis (DGGE) of the amplified 16S and 18S rRNA genes. Similarity clustering indicated that the intestinal microbiota derived from these four fish species could be divided into four groups based on 16S rRNA gene similarity, whereas the eukaryotic 18S rRNA genes showed no distinct groups. The water sample from the shared environment contained microbiota of an independent group as indicated by both 16S and 18S rRNA genes segments. The bacterial community structures were visualized using rank-abundance plots fitted with linear regression models. Results showed that the intestinal bacterial evenness was significantly different between species (P<0.05) and between species and the water sample (P<0.01). Thirty-five relatively dominant bands in DGGE patterns were sequenced and grouped into five major taxa: Proteobacteria (26), Actinobacteria (5), Bacteroidetes (1), Firmicutes (2), and Cyanobacterial (1). Six eukaryotes were detected by sequencing 18S rRNA genes segments. The present study suggests that the intestines of the four fish larvae, although reared in the same environment, contained distinct bacterial populations, while intestinal eukaryotic microorganisms were almost identical.     

Anisakis spp. larvae in three mesopelagic and bathypelagic fish species of the central Mediterranean Sea

In this work 437 fish samples of species belonging to the families Myctophidae (Electrona risso and Diaphus metopoclampus) and Phosichthyidae (Vinciguerria attenuata) were examined for the presence of Anisakidae larvae. The study was performed with fishes in the central Mediterranean Sea, particularly in the Strait of Sicily and in the Strait of Messina. The visual inspection and chloro-peptic analysis revealed the presence of nematode parasites with prevalence values between 2.9% in Electrona risso samples and 5.4% in Vinciguerria attenuata samples. A positive correlation was found between standard length (SL) and prevalence of infestation in D. metopoclampus samples (p < 0.05). The larvae examined were morphologically ascribed, at genus level, to Anisakis morphotypes I and II and molecularly identified as Anisakis pegreffii, Anisakis ziphidarum and Anisakis physeteris, in 67%, 9% and 24% of the fish samples examined. Overall, A. pegreffii and A. ziphidarum larvae were isolated in 14 and 2 specimens of D. metopoclampus respectively, A. physeteris larvae were found in 3 E. risso and 2 V. attenuata. A positive correlation was found between standard length and prevalence of infestation in D. metopoclampus samples (p < 0.05). First information is provided on the presence of Anisakis spp. larvae of the myctophid fish species E. risso, D. metopoclampus and V. attenuata from the Central Mediterranean. It is also confirmed the role of lanternfishes (Myctophidae) as paratenic hosts for Anisakis spp.     

The activity of ceftiofur sodium for Aeromonas spp. isolated from ornamental fish.

Our objective was to determine the activity of ceftiofur sodium against Aeromonas hydrophila and A. sobria isolated from a variety of domestic and imported tropical fish. Twelve antimicrobial drugs were tested for effectiveness against these aeromonads using the Kirby-Bauer Disk Diffusion technique and minimum inhibitory concentration determinations. Ceftiofur sodium was highly effective in vitro against aeromonads isolated from ornamental fish. Of the 42 isolates of Aeromonas spp. tested, none were resistant to ceftiofur sodium; however, all isolates were resistant to ampicillin, and 71% were resistant to tetracycline.     

The metal site as a template for the metalloprotein structure formation.

Achieving a thorough explanation of the behavior of metal sites in the formation of native metalloprotein structures is an exciting challenge in the biochemistry of metallobiomacromolecules. This study presents a personal insight into the subject. It is proposed that a metal center and its exogenous ligand compose a template. A template may impose a clear stereochemical preference on the loose peptide chains, and organize them into natural stereospecificity via the metal-ligand interaction, a long-range and strong interaction. Therefore, the stable peptide conformation induced by the template effect surrounding a template polyhedron could be called a template-mediated structural motif (TMSM).     

Molecular identification of two strains of third-stage larvae of Contracaecum rudolphii sensu lato (Nematoda: Anisakidae) from fish in Poland

Contracaecum sp. larvae (L3) from fish were identified using nucleotide sequences of the internal transcribed spacers ITS-1 and ITS-2 of the ribosomal DNA. The nematode larvae originated from fish in a freshwater situation (crucian carp Carassius carassius, from Selment Wielki Lake in Mazury, northeastern Poland) and a brackish-water region (Caspian round goby Neogobius melanostomus from the Baltic Sea, Gdafisk Bay at the Polish coast). Two strains (Contracaecum rudolphii A and B) of Contracaecum rudolphii senso lato, a parasite common at the adult stage in fish-eating birds, were identified. In fish from the freshwater site, only the strain temporarily designated C. rudolphii B was identified; in the brackish-water region, both strains were found, suggesting that fish serve as paratenic host for both genotypes. Contracaecum rudolphii sensu lato has been recorded in several species of fish-eating birds in Poland, particularly in the great cormorant, Phalacrocorax carbo, in which the abundance is highest. The results, although based on a restricted number of larvae, suggest that the life cycles of both genotypes can be completed in the Polish region and that at least one of them, C. rudolphii B, can develop both in fresh and brackish water.     

The limitations of heart rate as a predictor of metabolic rate in fish

Although telemetered heart rate (f_H) has been used as a physiological correlate to predict the metabolic rate (as oxygen consumption, V?O₂) of fish in the field, it is our contention that the method has not been validated adequately for fish. If f_H in fish is to be used to estimate V?O₂, a single linear (or log-linear) relationship must be established for each species between the two variables which allows V?O₂ to be predicted accurately under all environmentally relevant conditions. Our analyses of existing data indicate that while a good linear (or log-linear) relationship can be established between f_H and V?O₂, the conditions under which the relationship applies may be quite restricted. Physiological states and environmental factors affect the relationship between f_H and V?O₂ significantly such that several curves can exist for a single species. In addition, there are situations in which f_H and V?O₂ do not covary in a significant manner. In some situations f_H can vary over much of its physiological range while V?O₂ remains constant; in others V?O₂ may vary while f_H is invariate. The theoretical basis for this variability is examined to explain why the use of telemetered f_H in predicting V?O₂ of fish may be limited to certain specified applications.     

The caudal heart of fish: not a lymph heart

The caudal heart is traditionally regarded as part of the lymphatic vessel system in fish. Recently, however, a secondary blood vessel system has been demonstrated in this class of vertebrates, while the existence of lymphatics was questioned. In corrosion cats of the secondary system it is shown that the caudal heart functions as a venous pump in the secondary circulation. Contrary to current views fish do not have true lymphatic vessels. Theories on the phylogeny of lymphatics therefore should be revised accordingly.     

Caddis larvae (Trichoptera) as predators of fish eggs

SUMMARY. Eggs of bullhead ( Cottus gobio ) were found with damaged shells and with the contents removed. Experiments in laboratory aquaria indicated that the damage was caused by caddis larvae and that the type of caddis involved in egg predation might be identified by the nature of the shell damage.     

The potential of Isaria spp. as a bioinsecticide for the biological control of Nasutitermes corniger

The termite Nasutitermes corniger is a serious pest infesting urban areas of Brazil and many other countries. Control largely depends on synthetic pesticides whose indiscriminate use can impact the environment and the health of humans and other animals. Alternative strategies against insect pests, such as biological control by entomopathogenic fungi, could be effective while minimising these deleterious effects. We analysed the actions of the entomopathogenic fungi Isaria farinosa, Isaria fumosorosea, and Isaria javanica against the insect N. corniger. Our results indicated that the fungi examined were pathogenic against N. corniger, with I. farinosa ESALQ1355 being the most efficacious strain, resulting in the death of 95% of the workers (LC₅₀ 6.66?×?10⁴ conidia/mL) and 85% of the soldiers (LC₅₀ 6.81?×?10⁴ conidia/mL). This is the first report of the pathogenicity of Isaria spp. on N. corniger. These in vitro results suggest that I. farinosa ESALQ1355 demonstrates a significant biological potential for controlling N. corniger.     

Green fluorescent protein as a marker for Pseudomonas spp.

The development of sensitive methods for observing individual bacterial cells in a population in experimental models and natural environments, such as in biofilms or on plant roots, is of great importance for studying these systems. We report the construction of plasmids which constitutively express a bright mutant of the green fluorescent protein of the jellyfish Aequorea victoria and are stably maintained in Pseudomonas spp. We demonstrate the utility of these plasmids to detect individual cells in two experimental laboratory systems: (i) the examination of a mixed bacterial population of Pseudomonas aeruginosa and Burkholderia cepacia attached to an abiotic surface and (ii) the association of Pseudomonas fluorescens WCS365 with tomato seedling roots. We also show that two plasmids, pSMC2 and pGB5, are particularly useful, because they are stable in the absence of antibiotic selection, they place an undetectable metabolic burden on cells that carry the plasmids, and cells carrying these constructs continue to fluoresce even after 7 days in culture without the addition of fresh nutrients. The construction of improved Escherichia coli-Pseudomonas shuttle vectors which carry multiple drug resistance markers also is described.     

A technique for determining the distribution of pelagic fish larvae

A technique is described for studying small scale distributional patterns of fish larvae in the pelagic region. A plankton net is mounted beneath the bows of a small boat, the contents of the net are emptied continually by a suction pump. This system has advantages over previous techniques as it allows a large number of small discrete samples to be taken over a wide area in a short space of time. Preliminary results showed the population of perch larvae in Llyn Tegid is extremely clumped and the overall abundance of the larvae decreases as samples are taken progressively further away from the south-west end of the lake.     

The feeding of the larvae of Simulium austeni Edwards and Simulium (Wilhelmia) spp.

The possibility that the feeding rates of larvae of S. austeni and S. lineatum are influenced by the nature of the food material is considered in relation to natural river conditions and laboratory feeding experiments. Diatoms appeared to be the most satisfactory food source and bacteria (Pseudomonas) the poorest. Simuliid larvae attain high assimilation efficiencies when feeding on diatoms but the proportion of river suspended solids which they assimilate is probably very low.     

Relaxin increases rat heart rate by a direct action on the cardiac atrium.

Relaxin (Rlx) is best understood as a protein hormone of pregnancy that can influence pelvic and cervical connective tissue as well as uterine smooth muscle activity. Thus, it was unexpected that dense Rlx binding sites would be found in the rat cardiac atrium. To functionally characterize this finding, isolated rat atria were challenged with Rlx (0.3 to 30 ng/ml), and they responded with an increased rate (+36%) and force (+38%) of contraction Further studies in conscious normotensive and spontaneously hypertensive rats established by minipump circulating Rlx levels of about 0.5 and 5 ng/ml over 1 to 2 wks. There were significant increases in heart rate of 10-15%, with no consistent changes in blood or urine volume, water or food intake, and mean arterial pressure. We conclude that Rlx can directly stimulate rat cardiac atrial activity in vitro and cause chronotropy in vivo.