Fine structure of nerve-melanophore contacts in the angelfish Pterophyllum scalare

Contacts between small unmyelinated nerve fibres and dermal melanophores of the angelfish, Pterophyllum scalare, exhibit several features characteristic of synapses, including small synaptic vesicles and dense core vesicles, a narrow synaptic cleft, electron-dense material at the postsynaptic membrane (cell membrane of the melanophore) and, occasionally, presynaptic densities. An analysis of serial thin sections shows that the synapses described here represent varicosities of an otherwise more or less straight nerve fibre. A single axon thereby may form several en passant synapses with a single melanophore. It is suggested that the synaptic contacts described here not only represent sites of transmitter release but also play a role as sites of firm attachment between nerves and melanophores which guarantee a stable arrangement of nerve fibres and melanophores.Supported by the Deutsche Forschungsgemeinschaft     

Haemopoietic centres in the developing angelfish,Pterophyllum scalare (cuvier and valenciennes)

Summary The first haemopoietic centres in the embryo ofPterophyllum scalare are found in the blood islands of the yolk sac. These results are in contrast to the classical theory of blood formation in teleosts, which maintains that the first blood formation occurs intraembryonically, in the so-called intermediate cell mass of Oellacher. InPterophyllum, the intermediate cell mass forms only the axial blood vessels. Haemopoiesis in the post-embryo is carried out by the pronephros. This organ remains haemopoietic to the adult stage. In the adult, the pronephric tubules are degenerated; the organ is filled with haemopoietic tissue and also contains strands of adrenal tissue. The adult kidney (mesonephros) is also haemopoietic, though to a much lesser degree than the pronephros.The blood islands in the yolk sac form only stem cells (haemocytoblasts) and proerythroblasts. Released into the circulation, they differentiate and mature into round, disc-like erythrocytes (erythrocytes-E). Erythropoiesis in the pronephros produces elliptical erythrocytes (erythrocytes-ImA). Thus for the latter part of the postembryonic phase, until complete absorption of the yolk, there is a mixed erythrocyte population in circulation. During metamorphosis into the laterally-compressed adult, the adult type of erythrocyte (erythrocyte-A) makes its first appearance. Leucocytes and thrombocytes appear much later in development than the red blood cells. They are formed in the pronephros and are seen in circulation only after the yolk has been absorbed.     

Observations on rodlet cells found in the vascular system and extravascular space of angelfish (Pterophyllum scalare scalare)

In the angelfish ( Pterophyllum scalare scalare ) numerous rodlet cells were found in the large post-orbital blood vessel caudal to the eye and in the surrounding extravascular space. Within the vessel the rodlet cells formed striking regular arrays, along the inner aspect of the wall. The rodlets within the cells were positive to PAS but negative to Sudan Black B, Masson's, and the Fuelgen stain. The capsule around the cells was negative for all these stains. These rodlet cells appeared to be traversing the vessel endothelium, and to be pushing the endothelium aside without damaging it. Some discharged their contents into the vessel, but we never observed the release of intact rodlets. The nuclei of rodlet cells in actual contact with the vessel were at the end of the cell more distant from the endothelial wall. Cell-to-cell adhesion structures or communications junctions between rodlet cells and the endothelium were not evident. A putative rodlet cell precursor in the extravascular space contained large electron-dense granules, and extended pseudopodia that contacted nearby rodlet cells. Based on their morphology, tissue distribution, and their behaviour, we conclude that the rodlet cell is an endogeneous teleost cell type, and possibly represents a form of matured granulocyte.     

The influence of social rank in the angelfish,Pterophyllum scalare,on locomotor and feeding activities in a novel environment

To investigate differences in behaviour associated with social rank and environmental conditions, a comparison was made between swimming and feeding activities of dominant and subordinate angelfish, housed in groups of six, with those of angelfish housed singly in identical laboratory aquaria. Subordinate individuals were less active, less ready to feed and consumed less food items than dominants, but their feeding and activity levels were still greater than those displayed by isolated fish used as controls. When fish from each of the above categories were transferred to a novel, identical tank to be tested individually for a 6-day period, little change was observed in previously isolated fish. In contrast, the previous social experience had a marked influence on the behaviour of the other individuals, the effects being related to the social status. The strongest initial response to the new environment was shown by subordinate individuals, with a significant increase in swimming and a significant decrease in feeding compared to the group situation. Subordinates were significantly more active than dominants, who in turn moved more than previously isolated fish. Dominants and subordinates were now similarly reluctant to feed, and their food consumption was less than that of previously isolated fish. With time in the novel environment a significant reduction of swimming activity and a recovery of feeding measures were detected, but levels were still depressed in relation to the group condition, and lower in subordinates than in dominants, indicating the long-lasting effects of the previous social interactions. The results have clear implications for laboratory studies using groups of fish in which social hierarchies may be established prior to individuals being tested singly in a novel environment.     

Fatty acid composition,cholesterol and fat‐soluble vitamins of wild‐caught freshwater spiny eel,Mastacembelus simack (Walbaum, 1792)

Because of its local commercial value, the proximate nutritional composition, fatty acid composition, cholesterol and fat‐soluble vitamins of spiny eel (Mastacembelus simack Walbaum, 1792) were determined in 20 specimens caught in Keban Dam Lake, Elaz??, Turkey in September 2009. Moisture, protein, lipid, ash and cholesterol contents of the spiny eel were 75.9, 17.1, 10.9, 1.0% and 52.6 mg per 100 g, respectively. Fatty acid composition showed that total polyunsaturated fatty acids (PUFA) were the highest (37.1%), followed by monounsaturated fatty acids (MUFA, 35.5%) and saturated fatty acids (SFA, 27.4%). The relation between PUFA and SFA (1.35) was comparable to that of some fish species, and PUFA : MUFA : SFA ratio (1.35 : 1.29 : 1) was very close to that recommended by nutritionists. Among the vitamins (A, D, E and K) analyzed, the vitamin E content was highest followed by D, K and A. In conclusion, M. simack is rich in proteins, unsaturated fatty acids and vitamins and low in cholesterol, with a reasonable PUFA : SFA and PUFA : MUFA : SFA ratio as recommended by nutritionists. M. simack can therefore be recommended for human consumption as a good source of nutrition.     

Processing yield of wild‐caught and indoor‐reared Brazilian flounder Paralichthys orbignyanus

The aims of this work were to evaluate the fillet yield and the skin area production of wild‐caught (male × female) and indoor‐reared male Brazilian flounder Paralichthys orbignyanus. Fillet yield of wild‐caught Brazilian flounder is high, averaging 53.4 ± 0.7 and 51.2 ± 0.6% to female and male, respectively. However, indoor‐reared male flounder show even higher (P < 0.05) fillet yields of 59.4 ± 0.1%. Flounder weighing around 500 g should yield a skin area of ca. 450 cm², representing an important sub‐product that can be used in the fashion industry. The results of the present study emphasize the potential for culture and use of sub‐products of the Brazilian flounder.     

Sex‐specific effects of inbreeding in wild‐caught Drosophila melanogaster under benign and stressful conditions

In animal populations, sib mating is often the primary source of inbreeding depression (ID). We used recently wild‐caught Drosophila melanogaster to test whether such ID is amplified by environmental stress and, in males, by sexual selection. We also investigated whether increased ID because of stress (increased larval competition) persisted beyond the stressed stage and whether the effects of stress and sexual selection interacted. Sib mating resulted in substantial cumulative fitness losses (egg to adult reproduction) of 50% (benign) and 73% (stressed). Stress increased ID during the larval period (23% vs. 63%), but not during post‐stress reproductive stages (36% vs. 31%), indicating larval stress may have purged some adult genetic load (although ID was uncorrelated across stages). Sexual selection exacerbated inbreeding depression, with inbred male offspring suffering a higher reproductive cost than females, independent of stress (57% vs. 14% benign, 49% vs. 11% stress).     

Mating system of the Amazonian cichlid angel fish, Pterophyllum scalare.

The species, Pterophyllum scalare distinguishes itself by its breeding behavior, involving competition for territory, sexual partners, courtship and parental care. The purpose of this study was to identify the mating system adopted by this species of fish. Twenty males and twenty females were observed under semi-natural and experimental conditions to test the hypothesis of serial monogamy. Under semi-natural conditions, after the third breeding cycle, the couples changed mates. Under experimental conditions, the couples changed partners after the first breeding cycle. Under experimental conditions, mate recognition was investigated through the preference of the females, indicated by the time they spent with the males. The females were available or not for courtship from new males, depending on their aggressiveness or submission. The larger and more aggressive males obtained new mating opportunities while the submissive males were rejected by the females. The mated fish were aggressive towards intruders in the presence of the mate, protecting their pair bond. In the interval between breeding cycles, the couples did not display aggression towards intruders, confirming the hypothesis of serial monogamy. Best mate selection by the females and the opportunity of new matings for both sexes influenced the reproductive success of this species.     

A test of the relationship between cuticular melanism and immune function in wild‐caught Mormon crickets

Cuticular melanism and innate immune parameters can share common physiological pathways in insects, and this functional connection may contribute to the maintenance of insect colour polymorphisms. However, evidence linking colouration and immune function has been equivocal, particularly when tested in wild populations. The present study investigates phenotypic links between colouration and immune function in migratory Mormon crickets (Anabrus simplex, Haldeman), in which juveniles occur in conspicuous colour variants but mature to become uniformly melanic adults. Wild‐caught insects are used to evaluate the relationship between juvenile colouration and three immune parameters: encapsulation ability, lysozyme‐like activity and phenoloxidase activity. As nymphs, brown crickets are better able to encapsulate an inert implant introduced into the haemocoel than green crickets, although the difference is slight and ceases after they all become darkly‐coloured adults. By contrast, adults that develop from brown nymphs have a higher basal phenoloxidase activity than those that develop from green nymphs, regardless of the fact that all adults are brown. Intrinsic factors other than colouration exert larger effects on immunity: males show stronger encapsulation responses but lower phenoloxidase activity than females, suggesting a sex‐specific trade‐off between these two immune parameters, and adults exhibit higher immune function than nymphs. In summary, modest support is found for a correlation between cuticular melanism and increased immune function in wild Mormon crickets. Additional intrinsic factors such as developmental stage and sex appear to interact with colouration and have a more substantial connection to immune function in the wild.     

Capture of mass‐reared vs. wild‐like males of Ceratitis capitata (Dipt., Tephritidae) in trimedlure‐baited traps

The sterile insect technique (SIT) is widely used to suppress or eradicate infestations of the Mediterranean fruit fly, Ceratitis capitata (Wied.), an insect whose broad polyphagy poses a serious threat to fruit and vegetable crops. The SIT involves the production, sterilization and release of sterile insects to obtain sterile male by wild female matings, thus yielding infertile eggs. Mass‐rearing over many generations is known to produce dramatic changes in the behaviour and life history of C. capitata. This study investigated the possibility that mass‐rearing also alters male response to trimedlure, a sex‐specific attractant widely used in detection and monitoring programmes. We compared captures of released males from a mass‐reared strain and a recently established colony of wild flies in trimedlure‐baited Jackson traps at three spatial scales – open field, large field enclosures (75 m²) and small field cages (7 m²) – in two separate years. In the first year, males were used independently of flight ability, while in the second year only males with demonstrated flight capability were used. Trap capture was scored 2 days after release for the open field and the large field enclosures but either 1 h or 1 day after release in the small field cages. The findings were consistent across these different experiments: wild‐like males were captured in significantly greater numbers than mass‐reared males in both years of study, except in the trials lasting 1 day in the small field cages where significantly more wild than mass‐reared males were captured in 1 year but not the other. These results are compared with other studies, and their implications for SIT are discussed.     

Length–weight relationships for seven freshwater fishes caught in Kemer reservoir, Turkey

Length–weight relationships (LWR) were estimated for Acanthobrama mirabilis, Barbus pectoralis, Chondrostoma meandrense, Capoeta bergamae, Silurus glanis, Petroleuciscus smyrnaeus and Cyprinus carpio from the Kemer reservoir in western Anatolia, Turkey. This study is the first reference on length–weight parameters for five of these species.     

Fleeing towards death – leech‐induced behavioural defences increase freshwater snail susceptibility to predatory fish

Prey species are often exposed to multiple predators, which presents several difficulties to prey species. This is especially true when the response to one predator influences the prey’s susceptibility to other predators. Predator‐induced defences have evolved in a wide range of prey species, and experiments involving predators with different hunting strategies allow researchers to evaluate how prey respond to multiple threats. Freshwater snails are known to respond to a variety of predators with both morphological and behavioural defences. Here we studied how freshwater snails Radix balthica responded behaviourally to fish and leech predators, both separately and together. Our aim was to explore whether conflicting predator‐induced responses existed and, if so, what effect they had on snail survival when both predatory fish and leeches were present. We found that although R. balthica increased refuge use when exposed to predatory fish, they decreased refuge use when exposed to predatory leeches. When both predators were present, snails showed a stronger response towards leech than fish and responded by leaving the refuge. This response made the snails more susceptible to fish predation, which increased snail mortality when exposed to both fish and leech compared to fish only. We show that predators that have a relatively low predation rate can substantially increase mortality rates by indirect effects. By forcing snails out of refuges such as rock and macrophyte habitats, leeches can indirectly increase predation from molluscivorous fish and may thus affect snail densities.     

The morphology of the cement gland apparatus of Larval Pterophyllum scalare Cuv. & Val. (Cichlidae,Teleostei)

Summary The cement gland apparatus of newly hatched Pterophyllum scalare Cuv. & Val. was examined by histology, scanning and transmission electron microscopy. The whole organ is composed of three pairs of endoepithelial, ductless glands, which cause prominent elevations on the larval head and are found in a specific arrangement. Each single gland is represented by an aggregation of elongated, tubular secretory cells surrounding a pyriform acinus. It overlies a basal lamina and is covered by the outer layer of the bilaminar embryonic epidermis.Two different types of secretory cells can be distinguished. One type is restricted to the bottom of the cavity. It is characterized by multiform cytoplasmic protrusions, which project into the gland's cavity. The secretory granules contain a network of light filamentous material. The second type constitutes the side wall of the acinus. It does not develop any protrusions. The contents of the secretory granules is of very high and homogeneous electron density. The mechanism of extrusion is discussed for both cell types. All secretory cells show a strong PAS-reaction. In SEM a circular microridge pattern with attached mucus globules can be recognized on the larval epithelial surface.Dedicated to Prof. Dr. H. Leonhardt on the occasion of his 60th birthday     

Larval feeding behaviour of blind fish Astyanax fasciatus (Characidae), black tetra Gymnocorymbus ternetzi (Characidae) and angel fish Pterophyllum scalare (Cichlidae) fed zooplankton

We studied the feeding behaviour during the larval stages (from hatching until 8 weeks) of the Mexican blind fish Astyanax fasciatus, black tetra Gymnocorymbus ternetzi and angel fish Pterophyllum scalare using four zooplankton species (two rotifers: Brachionus calyciflorus and B. patulus and two cladocerans: Daphnia pulex and Moina macrocopa). Components of feeding behaviour (numbers of encounters, attacks, captures, ingestions, rejections and escapes) were quantified for 10 min observation periods per larvae. Data on the increase of the body length and mouth size of the three fish species during this period were also collected. When B. calyciflorus was used as prey, P. scalare showed higher capture and ingestion rates than A. fasciatus or G. ternetzi. With reference to age, B. calyciflorus was more frequently attacked, captured and ingested by G. ternetzi and P. scalare than A. fasciatus from the first to the 8th week. When offered B. patulus as prey, larvae of the three fish species showed increased consumption of B. patulus with time. A. fasciatus sometimes rejected B. patulus which could also escape after being captured. A. fasciatus began to attack and ingest Daphnia pulex and Moina macrocopa from the first week onwards while, G. ternetzi could neither capture nor ingest cladocerans until the fifth week. P. scalare began to ingest M. macrocopa and D. pulex from the third week onwards. These results are discussed with reference to the non-functional eyes of larval A. fasciatus.     

Structure,interaction and real‐time monitoring of the enzymatic reaction of wild‐type APOBEC3G

Human APOBEC3G exhibits anti‐human immunodeficiency virus‐1 (HIV‐1) activity by deaminating cytidines of the minus strand of HIV‐1. Here, we report a solution structure of the C‐terminal deaminase domain of wild‐type APOBEC3G. The interaction with DNA was examined. Many differences in the interaction were found between the wild type and recently studied mutant APOBEC3Gs. The position of the substrate cytidine, together with that of a DNA chain, in the complex, was deduced. Interestingly, the deamination reaction of APOBEC3G was successfully monitored using NMR signals in real time. Real‐time monitoring has revealed that the third cytidine of the d(CCCA) segment is deaminated at an early stage and that then the second one is deaminated at a late stage, the first one not being deaminated at all. This indicates that the deamination is carried out in a strict 3′ → 5′ order. Virus infectivity factor (Vif) of HIV‐1 counteracts the anti‐HIV‐1 activity of APOBEC3G. The structure of the N‐terminal domain of APOBEC3G, with which Vif interacts, was constructed with homology modelling. The structure implies the mechanism of species‐specific sensitivity of APOBEC3G to Vif action.     

Effects of aggregative behaviour on the bioenergetics of the freshwater predatory leech Nephelopsis obscura (Erpobdellidae)

1. Supplied with ad libitum prey, the effects of different group sizes (one, five, ten, twenty-five, fifty or 100) on the acquisition and allocation of energy were examined over the entire life cycle of the freshwater predatory leech Nephelopsis obscura , to evaluate the bioenergetic costs and/or benefits of aggregation.
2. In terms of growth, asymptotic biomass and ingestion, group sizes larger than one and less than ten are optimal. As group size increases from ten to 100, N. obscura has slower growth and lower weekly food ingestion, suggesting interference competition. Single leeches had lower food consumption than group sizes of less than 100 animals. With a lower asymptotic biomass, single leeches have lower fecundity and presumed lower fitness. Lipid deposition was unaffected by group size.
3. Size- and time-specific respiration rates declined with increasing group size. For group sizes between five and fifty, the same relative proportion of ingested energy was allocated to respiration. Above this threshold group size, leeches allocated a higher proportion of ingested energy to growth, i.e. had higher growth efficiency, as did leeches cultured individually.
4. In the largest group size, total time spent in activity was highest (reflecting the high degree of interference between conspecifics), but as a result of the lower hourly costs of respiration they allocated a lower proportion of ingested energy to total respiration.
5. Optimum group size of N. obscura in the laboratory is within the typical range of group sizes found on stony shores in the field.     

Effects of aggregative behaviour on the bioenergetics of the freshwater predatory leech Nephelopsis obscura (Erpobdellidae)

1. Supplied with ad libitum prey, the effects of different group sizes (one, five, ten, twenty-five, fifty or 100) on the acquisition and allocation of energy were examined over the entire life cycle of the freshwater predatory leech Nephelopsis obscura , to evaluate the bioenergetic costs and/or benefits of aggregation.
2. In terms of growth, asymptotic biomass and ingestion, group sizes larger than one and less than ten are optimal. As group size increases from ten to 100, N. obscura has slower growth and lower weekly food ingestion, suggesting interference competition. Single leeches had lower food consumption than group sizes of less than 100 animals. With a lower asymptotic biomass, single leeches have lower fecundity and presumed lower fitness. Lipid deposition was unaffected by group size.
3. Size- and time-specific respiration rates declined with increasing group size. For group sizes between five and fifty, the same relative proportion of ingested energy was allocated to respiration. Above this threshold group size, leeches allocated a higher proportion of ingested energy to growth, i.e. had higher growth efficiency, as did leeches cultured individually.
4. In the largest group size, total time spent in activity was highest (reflecting the high degree of interference between conspecifics), but as a result of the lower hourly costs of respiration they allocated a lower proportion of ingested energy to total respiration.
5. Optimum group size of N. obscura in the laboratory is within the typical range of group sizes found on stony shores in the field.