Escape of farmed tilapiines into the wild and entry of wild forms in fishponds,and the possible interactions between wild and farmed tilapiines from a sample of smallholder farms in Central Uganda

Seven smallholder fishponds in central Uganda were studied between 2000 and 2001 to investigate the interaction of farmed tilapiines with their wild conspecifics. Emphasis was on the features that facilitate escape of fish and/or entry of fish into the farms and interactions between the farmed and the wild. These included number of species, source of seed, connection between pond and natural watercourses, purpose of the farm, destination of cultured fish and interaction between farmed and wild fish. Fishponds had no screens against entry of wild fish into the farm or escape of farmed fish into the wild and occurred within wetlands close to natural watercourses. Ponds stocked with one fish species were found to have multispecies with some individuals that were apparently intermediate morphs between the species. Fry produced within the growout fishponds was shared with other farmers within and outside the watersheds. This study showed that smallholder farms with little or no control of escape or entry of fish out and into the fishponds, and little or no management present circumstances that facilitate continued movement of tilapiines within and across watersheds in Ugandan waters. The study also indicated possible genetic interaction between farmed and their wild conspecifics through interactions within fishponds.     

Occurrence of stones, sediment and fish scales in stomach contents of demersal fish of the Rockall Trough

The occurrence of stones, sediment and fish scales was determined among the stomach contents of some 5000 fish. These fish comprised representatives of more than 70 different demersal species, sampled at 250 m bathymetric intervals, from the Rockall Trough, northeastern Atlantic Ocean, at depths ranging from 500 to 2900 m. Stones only occurred in stomachs of fish caught at 500–1000 m depth, their incidence in stomachs with food present being 4.6% at 500m, 1.1% at 750 m and 1.3% at 1000m depth. Sediment occurred in 9%, fish scales in 7%, of stomachs with contents. Sediment and scales co-occurred in the stomachs of primarily benthopelagic feeding fish. The sediment, however, was associated with the less dominant epibenthic components of the diets while the scales occurred with the more common benthopelagic components. The co-occurrence of sediment, scales and benthopelagic prey may arise through the former items having longer residence times in the stomachs than, for example, epibenthic prey. There is no evidence of increased occurrence of sediment (and its associated meiofauna) in the diets of fish on the lower slope at depths of 1500–2900 m in the Rockall Trough.     

Reactivation of koi herpesvirus infections in common carp Cyprinus carpio

Two co-habitation studies with common carp were conducted to determine whether latent infections of koi herpesvirus (KHV) exist. Fish were exposed to KHV using 2 different temperature profiles, which induced low and high initial mortality. Subsequently, certain groups of fish were co-habited with naive fish while others were not. Koi herpesvirus was reactivated in fish from 3 of the 5 experimental tanks. Reactivation of the virus occurred regardless of the initial mortality associated with the virus or whether fish were co-habited with naive fish. The reactivation of the virus in our experiments occurred several months after the initial exposure to KHV and appeared to be temperature dependent.     

The importance of shading by riparian vegetation and wetlands in fish survival in stagnant water holes,Great Ruaha River,Tanzania

Mass fish mortality occurred in November 2006 in a water hole in the Great Ruaha River, Ruaha National Park, and was due to the lack of shade by riparian vegetation or fringing wetlands. Nearby water holes with shade or fringing wetlands suffered no fish mortality. Despite being vulnerable to intense birds’ predation, fish stayed in the top few centimeters due to hypoxia in deeper water.     

Threat Sensitivity in Bicolor Damselfish: Effects of Sociality and Body Size

Threat sensitivity involves graded antipredator responses that reflect the degree of predatory threat encountered. Models of predatory Atlantic trumpetfish (Aulostomus maculatus) were presented to differently sized juvenile bicolor damselfish (Pomacentrus partitus) that occurred singly or in small groups to test for threat sensitivity. Bicolor damselfish displayed threat sensitivity by responding more strongly: 1. To large models than to small models; and 2. As models were brought closer. Solitary damselfish showed stronger responses than did fish in small groups. However, no habituation to threat occurred, no correlation was found between response strength and fish size, and many individuals gave strong, ungraded responses to predator models. Comparisons between juvenile bicolor damselfish and threespot damselfish suggest that bicolor are weakly threat sensitive in that they respond strongly regardless of threat (hypersensitivity). Solitary fish are more hypersensitive than grouped fish. Threespot damselfish show a stronger influence of damselfish body size: small threespot exhibit graded responses in proportion to degree of threat (pure threat sensitivity), whereas large threespot show relatively weak responses (nonchalance). These interspecific comparisons indicate the potential range that characterizes threat sensitivity and the possible influence of social and ontogenetic factors on that range.     

Epidemic trichodinosis associated with severe epidermal hyperplasia in largemouth bass, Micropterus salmoides, from North Carolina, USA

An epidemic of trichodinosis associated with severe epidermal hyperplasia occurred in adult largemouth bass (Micropterus salmoides) from the Chowan River drainage, North Carolina (USA) in late winter to early spring 2002. Initial reports by anglers of fish with a "jelly-like slime coat" on the skin prompted an electrofishing survey in which about 10% of sampled largemouth bass had a very thick, bluish-white "mucoid layer" on the body and fins. Moderate to heavy infestations of the ciliate Trichodina were detected in wet mounts of skin from five of five fish having the mucoid layer; these fish also had significant gill infestations. An additional two fish with only mild reddening and four asymptomatic fish (no skin lesions) had mild skin infestations but no gill infestations. Two asymptomatic fish had no skin parasites. Four fish with the mucoid layer were necropsied and had extremely severe epidermal hyperplasia on the body and fins. The hyperplasic epidermis had relatively few mucus cells and typically was about 5-10 times thicker than healthy epidermis. The upper four fifths of the epidermis consisted of finely vacuolated, highly flattened, somewhat disorganized epithelial cells. No other significant clinical or histopathologic abnormalities were detected. No systemic infection by pathogenic bacteria was noted. The environmental cause of the epidemic is uncertain but the lesions suggest that some chronic stressor was involved.     

Social conditioning and dominance in male betta splendens

To determine whether social conditioning modifies relative dominance in the Siamese fighting fish ($\text{Betta splendens}$), individual fish were matched for gill cover erection frequency (GCEF) to a mirror. One member of each pair experienced a series of four winning encounters (dominants) while the other of the pair experienced four losing encounters (subordinates). After the fighting experience, matched pairs were placed together and aggressive responses of both fish were recorded. Fish experiencing wins displayed significantly more and were more aggressive than fish experiencing losses which showed significantly higher levels of avoidance. However, no change in mirror GCEF occurred as a result of differential experience.     

Vertebral abnormalities in white crappies, Pomoxis annularis Rafinesque, from Lake Decatur, Illinois, and an investigation of possible causes

Crappie, Pomoxis annularis , from Lake Decatur, Illinois, were reported to have a high incidence of backbone deformities, an investigation was initiated to determine both the mechanism of vertebral injury and the causative agent. Three groups of fish were collected: normally shaped and abnormally shaped crappies from Lake Decatur and control fish from abnormally shaped crappies from Lake Decatur and control fish from nearby Lake Sangchris. Analysis of organic and inorganic residue levels in fish tissue revealed no significant levels of contaminants in any of the three groups. Evaluation of the mechanical properties, biochemical composition, and density characteristic of vertebral bone showed no significant difference between the three groups. A myxosporidean parasite, found in both normal and abnormally shaped crappies from Lake Decatur, may have been a contributing factor leading to the spinal deformities. We believe that a short-term exposure to organophosphate insecticides, may have occurred causing muscular contractions and resulting in vertebral damage and abnormally shaped fish.     

Changes in Histamine Content in Fish Products for Animal Feeds and in Aqueous Solution by Gamma-Irradiation

The irradiation effects on histamine in fish meals and fish solubles for animal feeds and in aqueous solution were investigated. The amount of histamine in fish meal (0.4mg/100g) was not changed by up to 5.0 Mrad (50kGy), while the histamine content in fish soluble (45.7 mg/100 g) decreased ca. 16% at 5.0 Mrad. There occurred no accumulation of histamine by irradiation or during storage.

The G values of histamine formation from histidine solution and histamine decomposition by irradiation in deoxygenated neutral solutions were 0.077 and 1.90, respectively. Oxygen inhibited the formation of histamine from histidine but it had little effect on histamine decomposition. Nitrous oxide accelerated the decomposition of histamine and inhibited the accumulation of histamine in histidine solution by irradiation. These results show that there is no problem of histamine accumulation in feedstuffs caused by irradiation since the decomposition of histamine is preferred to its formation.     

Reef-based micropredators reduce the growth of post-settlement damselfish in captivity

Despite the ubiquity of micropredators and parasites on coral reefs, their effects on the survival and growth of juvenile fishes are virtually unstudied. Caging and laboratory experiments were used to investigate whether reef based micropredators fed on recently metamorphosed damselfish, the time of day that micropredation occurred, and whether micropredation affected fish growth and survival. Caged juveniles of the damselfish, Pomacentrus moluccensis, were held on the reef over four consecutive time periods. Micropredators (gnathiid and cirolanid isopods) were found associated with caged fish at night only, and cirolanids were observed attacking and killing some caged fish. In order to test the effect of micropredation on growth and survival without the influence of predatory fishes, groups of five P. moluccensis were caged for 2 weeks in one of three treatments: micropredators excluded, mesh control, or micropredators present. There were no significant differences in survival among the treatments, but fish were larger in cages with fewer survivors suggesting that competition for food was intense. Fish exposed to micropredators were larger than fish in the other two treatments, however, micropredator exclusion also excluded plankton; thus, differences in food availability among treatments during crepuscular periods likely confounded the treatment effect on fish growth. A laboratory growth experiment was performed to better control food availability and minimise handling stress, using a validated host-micropredator model. Individual juvenile damselfish, Dischistodus perspicillatus, were exposed to 0, 1 or 2 micropredators (Gnathia falcipenis) each evening and fed equally for 8 days. Mortalities only occurred in fish exposed to micropredators on the first evening of the experiment, and fish exposed to two micropredators each evening were significantly smaller than unexposed fish. These results suggest that repeated gnathiid infections can reduce fish growth in the first week after settlement. Consequently, micropredation may affect the ecology of damselfish after settling on coral reefs.     

Ultraviolet absorbance of the mucus of a tropical damselfish: effects of ontogeny, captivity and disease

The ultraviolet (UV) absorbance of the mucus of a Great Barrier Reef damselfish Pomacentrus amboinensis was investigated with regard to ontogeny and time spent in captivity. The UV absorbance of P. amboinensis mucus increased with fish size and decreased with time spent in captivity. The wavelength of maximum absorbance of the mucus did not change with fish size, but shifted towards shorter wavelengths with increasing time spent in captivity. The UV absorbance of the mucus of fish with 'fin rot' was compared to that of similar healthy individuals, and a significant decrease in UV absorbance of unhealthy fish mucus was detected; no wavelength shifting occurred. Pomacentrus amboinensis appears to sequester mycosporine-like amino acids from the diet in order to protect epithelial tissues from UV damage, and decreases in UV absorbance in captive fish were probably due to insufficient dietary availability.     

Effects of a fish oil rich diet on hyperoxic lung damage in mice

Mice were fed a chow diet plus 10% cellulose, 10% fish oil or 10% sunflower oil for 3 weeks, then exposed to 100% oxygen for 75 h. Large changes in lung fatty acid composition occurred, but this did not affect hyperoxic lung damage nor levels of thiobarbituric acid reactive substances or myeloperoxidase in lungs of mice following exposure to hyperoxia. Thus there is no evidence that the ingestion of large quantities of fish oil increased the susceptibility to the oxidative stress induced by hyperoxia.     

Habituation,reinstatement and recovery of predatory responses in two species of teleosts, Carassius auratus and Macropodus opercularis

The tendency for predatory responses to habituate and to be reinstated through sensitization and the passing of time was studied in two species of fish (the goldfish and the paradise fish). Prey (live brine shrimp), confined in a clear plastic tube were presented for short daily exposures to individual fish. Bites directed at the stimulus tube containing the prey were the primary response measure. In both species biting decreased significantly over the 6 days of the experiment. Reinstatement of the habituated response occurred by two means: (1) reinforcement (i.e. allowing the fish to chase and consume the prey), and (2) passing of time (10 days) with no intervening stimulation (recovery). Reinstatement could not be produced by presenting a novel stimulus, nutritive stimuli, nor by a shorter recovery interval.     

Report of a large fish kill resulting from natural acid water conditions in Australia

A large natural fish kill which resulted in the deaths of a total of more than 3400 fish comprising eight different species occurred in a freshwater billabong (lagoon or small permanent waterbody) on the Magela Creek in the subtropical Northern Territory of Australia in January, 1980. The fish deaths were assessed to be the result of a combination of natural acid water runoff into the billabong and resultant elevated aquatic biotoxic aluminium levels. Details of water quality changes which occurred during the event and analytical data for the fish killed are provided, together with some explanation of the sequences of occurrence of the fish kill.     

Fish population changes in the Volta lake in Ghana during its first sixteen months

Summary A study has been made on changes which have occurred in the fish fauna as a result of the formation of the Volta Lake in Ghana. The data on the relative abundance of fish in the Lake were compared with those obtained from fish landings on the Black Volta and from the Niger river survey, as no observations of fish abundance were made on the Volta River before the Akosombo dam was closed. General changes in the relative abundance of the most important families of fish are described and the changes in the relative abundance of six feeding types in the Volta Lake and Black Volta, based on more than 700 stomach and gut analyses of 50 species of fish, are compared with those of the fish found in the Zambezi River and Lake Kariba in Central Africa.The most characteristic features of the changes in fish fauna are an increase in plankton feeders, so that these are becoming dominant in some areas; a great decrease in mormyrids in the Lake as compared with the river, and a similar drop in the characid Alestes, while Tilapia has increased. These changes are not uniform throughout the lake, and differences are most marked along the North-South axis.Department of Zoology and Volta Basin Research Project, University of Ghana     

基于水声学方法的天目湖鱼类季节和昼夜空间分布研究

采用水声学方法系统地对天目湖春夏秋冬四季鱼类水平和垂直空间分布进行了调查研究,同时对昼夜探测的差异性进行了比较,并对不同季节间鱼类聚群形态进行了探讨。研究结果表明,天目湖鱼类在不同季节间存在规律性水平迁移,从全湖角度分析,天目湖鱼类资源昼夜间的水平空间分布无明显差异特征,但在春末和夏季的局部区域里,昼夜间鱼类存在一定近岸—远岸的水平迁移;不同季节和昼夜间,鱼类垂直分布差异明显,且在存在温跃层的夏季7月昼间,鱼类密度垂直分布与水温的垂直分布关系密切,温跃层以下的鱼类密度基本为0;天目湖鱼类在四个季节都属于成群分布类型,但季节间鱼类聚群形态不同,在冬季的1月呈现出典型的聚集,相对于昼间,春夏季鱼类在夜间分布更为均匀、分散,且水平探测表明在夜间水体表层存在大量鱼类分布。     

Gyrodactylus salmonis (Yin and Sproston, 1948) parasitizing fry of Salvelinus fontinalis (Mitchill)

Fry of brook trout, Salvelinus fontinalis (Mitchill), were infected under controlled conditions with Gyrodactylus salmonis (Yin and Sproston, 1948) and the course of infection followed for 22 days in four groups of 40 fish and for 60 days in a group of 200 fish. Between 15 and 44% mortality occurred among infected groups compared with less than 5% in noninfected control groups. Intensely infected moribund fish were cachexic, lethargic, and often darkened in color. Histologic studies revealed that intensely infected fish had a thinner epidermis with fewer goblet cells than control fish. Internally the only obvious lesions involved the kidney where there was extensive tubular degeneration and necrosis. It is hypothesized that attachment and grazing activity by G. salmonis can lead directly to death of fry through disruption of the osmotic permeability of the epidermis. There was no evidence of secondary invasion by bacteria or fungi.     

Collapse of the reproductive process of two migratory fish (Prochilodus argenteus and Prochilodus costatus) in the Três Marias Reservoir,São Francisco River,Brazil

Generally, migratory fish can complete vitellogenesis even when the migration process is interrupted; however, final oocyte maturation does not occur and therefore there is no spawning. To evaluate the reproductive process of migratory fish inside the reservoir of the Três Marias Dam (a lentic environment), 90 female and 81 male Prochilodus argenteus and 172 female and 115 male Prochilodus costatus were captured in this environment. Males and females from both species in the resting stage were pre‐dominant, and the highest frequency of specimens in advanced maturation stages occurred in November, December and January. According to histological analysis, ovarian regression was frequent and vitellogenic oocytes undergoing atresia were intensely observed, moreover, no fish with ovaries and testes with characteristics of spawning and spermiation, respectively, were captured. This indicated that both species were preparing for reproduction and reaching advanced gonad maturation, but were unable to complete the process of reproduction in this environment. The data from this study indicate that the modification of portions of rivers to lentic environments can have a negative impact on the reproductive process of migratory fish in freshwater.     

Movements and dispersal of farmed Atlantic salmon following a simulated-escape event

One of the major challenges for understanding the ecological impact of escaped farmed Atlantic salmon (Salmo salar L.) is predicting their dispersal patterns after an escape event. Here, we quantify the behaviour of escaped farmed salmon using a simulated-escape experiment within a Norwegian fjord system. Thirty-seven individuals were tagged with acoustic transmitters and their spatial distribution, horizontal movements and diving behaviour was monitored throughout the fjord and accompanying rivers using 29 acoustic receivers. A rapid movement away from the release site occurred. There was no movement into the rivers feeding the fjord and there was no preference for residence at the fish farms: nearly a third of the individuals had a final detection in the outer part of the fjord and no detections occurred from approximately 2 months after release. As it is unlikely that all fish died or remained undetected within the study area it is reasonable to assume that a substantial proportion of the fish moved out of the fjord system. If a recapture program is not implemented immediately after an escape event, we recommend spreading potential recapture efforts over a relatively large area.     

Plasma amino acid levels in rainbow trout (Oncorhynchus mykiss)

The time course of plasma amino acid concentrations was studied in adult rainbow trout (300 g mean body weight). After a starvation period of 2 days fish were force-fed either with fish protein concentrate or a mixture of acidic casein and Na-caseinate at a rate of 0.32% CP (N' 6.25) of body weight. Peak levels occurred for feeding fish protein concentrate 6–12 h and for the casein mix 18 h post-feeding. The increase of the essential amino acids was closely correlated to the amino acid profile of the test proteins, whereas the concentration differences of the non-essential amino acids were at no time correlated to the amino acid pattern of fish protein concentrate or even negatively correlated in case of casein. The limiting amino acids in the test proteins were determined by ranking the average concentration increases (decreases) of the individual essential amino acids. Accordingly, arginine and histidine were most deficient in casein; in fish protein concentrate tryptophan seems to be the first limiting amino acid, followed by isoleucine.