Feeding habits of the African bagrid,Chrysichthys filamentosus in a Nigerian lake

The feeding ecology ofChrysichthys, a commercially important freshwater bagrid in Nigeria, is described from a southeastern lake. Over a year period, 779 stomachs were examined. The main food items were chaoborid and chironomid larvae, ostracods, copepods and detritus. Larger fish fed mostly on insect larvae and detritus while the smaller individuals consumed mostly microcrustacea. Feeding intensity was lowest during the height of the flood. There was little diel change in the amount of food consumed. The fish are morphologically pre-adapted for their benthic omnivorous feeding habits.     

Comparison of growth, diet and food consumption of sea-run and lake-dwelling Arctic charr

Sea-run post-smolt Arctic charr Salvelinus alpinus , (15–26 cm) from Storvatn, northern Norway (70°39'48"N) had significantly higher average specific growth rates in two years (1·64 and 1·66) than the corresponding lake-dwelling charr (0·53 and 1·20). The post-smolts displayed fast compensatory growth in the first 2–3 weeks of their sea residency, but then almost stopped growing prior to their return to fresh water. Lake-dwelling charr grew more evenly during the same time period. Thus, the anadromous charr may return to the lake after only 5–6 weeks in the sea, because the potential to maintain a high growth rate in the sea is reduced. The marine diet consisted mainly of the two crustacean plankton species Calanus finmarchicus , and Thysanoëssa , sp. (88%), and less of fish (6%), insects (4%) and benthos (2%). The diet of lake-dwelling charr consisted mainly of insects (58%, mostly chironomid pupae) and zoobenthos (29%), and less of zooplankton (13%) during the same time period. Although post-smolts had the highest growth rates, they had significantly lower food consumption rates and higher frequencies of empty stomachs than the corresponding lake-dwelling fish. Possible explanations for this paradox are discussed in relation to stomach evacuation rates, water temperature, feeding behaviour and the energy content of the food in the two environments.     

Feeding and prey-selection of wild Atlantic salmon post-smolts

The diet of post-smolt Atlantic salmon Salmo salar caught in the Trondheimsfjord and Frohavet in central Norway, based on stomach contents analysis, showed a gradual change during migration from the river to the estuary, fjord and coastal areas. Post-smolts caught in the estuary had eaten intertidal gammarid amphipods, while post-smolts caught further seawards preyed upon available marine prey such as Calanus spp., adult euphausiids and fish larvae. The frequency of adult insects was high in all post-smolt stomachs. The gradual change in diet suggested that feeding conditions in the early marine phase were important for post-smolt survival and growth. With the exception of the copepods, there was no overall similarity between species composition of the plankton samples and the stomach contents. Although the hypothesis that the post-smolts are opportunistic feeders cannot be rejected, the composition of the stomach contents suggests a possible selectivity of advantageous prey.     

Long‐term changes in the feeding of Pollachius virens on the Scotian Shelf: responses to a dynamic ecosystem

The diet and feeding ecology of pollock Pollachius virens from the Scotian Shelf and Bay of Fundy in the north‐west Atlantic changed over the last few decades, which was associated with decreases in euphausiid abundance. Stomach contents data for 2078 pollock collected during the 1958–1967 period and for 1230 pollock collected during the 1996–2002 period indicated that pollock diet contained fewer euphausiids and feeding activity decreased. During the early period, euphausiids were present in 65% of the pollock stomachs that contained food and only 9% of these stomachs in the recent period. The decrease of euphausiids was not wholly offset by an increase in piscivory, since there was little increase in the frequency of fish prey in the diet or in the fullness index for this prey type. Empty stomachs were significantly more common in the recent period during both the winter and summer. The decreased occurrence of euphausiids in stomach samples coincided with a significantly decreased abundance of this prey, suggesting that the near‐absence of euphausiids in recently collected pollock stomachs reflected prey abundance. Concurrent with changes in diet and feeding intensity, the condition or 'plumpness' of pollock significantly declined from the early to the late sampling periods.     

Feeding habits of megrim, Lepidorhombus whiffiagonis (Walbaum, 1792), from the central Adriatic Sea

The feeding habits of the megrim, Lepidorhombus whiffiagonis , from the central Adriatic Sea were investigated with respect to fish size and seasons. Stomach contents of 510 specimens, 9.0–28.9 cm total length (TL), collected by bottom-trawl from 2004 to 2006 were analyzed. The percentage of 97 empty stomachs varied significantly with season (maximum during the winter, 32.1%; minimum during summer, 7.4%). The food composition suggests that the megrim is a carnivorous fish. Prey items identified in the stomachs belong to four major groups: Teleostei, Decapoda, Mysidacea and Cephalopoda. Teleosts were the most important (%IRI = 82.2), especially in fish larger than 14 cm TL. Mysidacea constituted the main prey for fish less than 14 cm TL. At the species level, the teleost Antonogadus megalokynodon (%IRI = 1.5) and decapod Processa canaliculata (%IRI = 0.9) were the most frequent prey. The mean weight of stomach contents increased significantly for fish larger than 14 cm TL, while the mean number of prey items did not differ significantly among size classes. Diet composition showed little seasonal variation; teleosts were the most important prey in all seasons, especially during spring. The lowest intensity of feeding recorded in winter could be related to the lower sea temperature and to the spawning period.     

The basis of food selection in flounders, Platichthys flesus (L.), in the Severn Estuary

The factors influencing the selection of food by flounders, Platichthys flesus (L.), have been investigated by analysing collections made in the Severn Estuary for 1 year and the results of experiments. Flounders measuring between 6–0 and 35 cm fed heavily on the polychaete Nereis diversicolor in February and on the amphipod Gammarus salinus between February and April. Thereafter these species were replaced by the mysid Neomysis integer with the decapod Crangon vulgaris. Flounders shorter than 6.0 cm, fed mainly on Neomysis integer regardless of month. Numerous factors were involved in the choice of the food including (1) the maximum and minimum length of prey, (2) its spatial distribution in the water column, (3) its degree of concealment, (4) its motility and ability to escape predation, (5) conditioning of the flounders for certain foods, (6) the fish's swimming speed and (7) the turbidity and temperature of the water.
Although the average length of ingested prey remained unchanged as the fish grew in size, an increase in the maximum and minimum lengths was observed. The percentage of stomachs that contained no identifiable remains in flounders greater than 6–0 cm averaged 80–95 % during part of the winter and 60% in the summer and between January and March. These changes partly reflected the influence of low water temperature on the metabolic rate and availability of prey. The dry weight of the stomach contents in flounders longer than 6–0 cm was lowest in winter but high values were recorded in the spring. This latter feature was probably because the rate of feeding was greater than that of digestion. During the summer, under more normal feeding conditions, the weight of the stomach contents remained relatively low compared to other fish populations. Flounders shorter than 6–0 cm always contained more food in their stomachs on a unit weight basis than larger individuals, reflecting metabolic rate and hunting efficiency.     

Food and feeding habits of the African catfish Clarias gariepinus (Burchell, 1822) (Pisces: Clariidae) in Lake Koka,Ethiopia

The food and feeding habits of Clarias gariepinus (Burchell, 1822) were studied in Lake Koka, Ethiopia, in May 2011 (dry month) and September 2011 (wet month). Three hundred and thirty eight nonempty stomach samples were analysed using frequency of occurrence and volumetric methods of analysis. Detritus, insects, macrophytes, zooplankton and fish were the dominant food categories by occurrence, and they occurred in 79.6%, 63.6%, 63.0%, 56.2% and 15.4% of the stomachs, respectively. Volumetrically, the above food items comprised 24.3%, 14.1%, 14.5%, 19.3% and 21.8% of the total volume of food categories. Phytoplankton and gastropods were of low importance, and they occurred in 28.7% and 8.6% of the stomachs, respectively. Their volumetric contributions were 3.2% and 2.8% of the total volume of food categories. During the dry month, fish, zooplankton, insects and detritus were important food categories, while during the wet month detritus, macrophytes, insects and gastropods were important. Smaller catfish diets were dominated by detritus, macrophytes and insects, whereas larger catfish shifted to fish and zooplankton. Based on the results, C. gariepinus was found to be omnivorous in its feeding habits in Lake Koka.     

Sea trout in North Argyll sea lochs: II. diet

The diet of sea trout in some of the sea lochs of the west coast of Scotland was investigated. The contents of 986 sea trout stomachs from the Loch Etive area (1970–1973), and 291 stomachs from the Loch Eil area (1964–1973), were examined and the composition of the diet, seasonal changes and the effect of trout size were analysed using frequency of occurrence, dry weight and number of organisms methods. Benthic feeding (crustacea and annelids) was more important in winter while midwater and surface organisms (young fish and insects) were preferred in summer. Young fish (mainly clupeids and sand eels) featured more in the diet of larger trout (≤21 cm) than in the smaller size range (≥21 cm). Surveys of 24-h were completed in June and September, 1972, and indicated that availability of food was the main factor influencing the presence or absence of trout. Bottom feeding was greatest during the day while the amount of midwater and surface feeding tended to increase between sunset and sunrise.     

Estuarine recruitment of a marine goby reconstructed with an isotopic clock

Information on movement patterns of marine fishes between estuarine populations and stocks at sea is fundamental to understanding their population dynamics, life history tactics and behavior. Furthermore, understanding estuarine habitat use by marine fishes is crucial for their effective conservation and integrated estuarine management. Although large numbers of young marine fish make use of temperate estuaries in highly predictable abundance patterns, very little is known about how estuarine populations interact with the populations at sea. Recruitment of sand goby Pomatoschistus minutus (Pallas, 1770) into the low salinity zone of the Scheldt estuary (Belgium) was reconstructed over an entire year by means of an isotopic clock. These results were combined with a growth model to yield age and length at immigration. Sand gobies entered the upper Scheldt estuary almost continuously from May onwards, except in July when they appeared to avoid the estuary due to warm summer temperatures. About 70% of the fish caught in the upper estuary resided there for less than 1 month, which indicates a strong temporal overlap of immigration and emigration. This complex migration pattern suggests that estuarine residence is caused by trade-offs made at the individual level, whereby migration is probably triggered by temperature. The high turnover of individuals in the estuarine population leads us to question the functional role of the estuary for marine fishes. Sand gobies entering the upper estuary had a wide range of ages and body sizes, although they were at least 2 months old and had a minimum standard length of approximately 20 mm. This study shows that the use of an isotopic clock strongly complements catch data and is useful to describe the connectivity between populations.     

The characteristics of feeding of Diaphus theta (Myctophidae) in the northwestern part of the Pacific Ocean in the Summer-Autumn period

The feeding of Diaphus theta in the zone of the subarctic front and in Pacific waters off the Kuril Islands in November 2001 and in July–August 2002 was studied. Interzonal plankton [euphausiids (mainly Euphausia pacifica), copepods (Metridia pacifica), and amphipods (Themisto pacifica)] dominated in the food bolus. As fish grow, the proportion of copepods decreases, the proportion of euphausiids and amphipods increases in stomachs, and the food spectrum extends. One considerable peak in the feeding (in both the summer and autumn periods) occurring in the nighttime was revealed. The most intensive feeding takes place in the dark time of the day in the epipelagial due to euphausiids and amphipods; in the light time of the day, the feeding activity declines. Fish feed mainly on copepods in the upper pelagial. The daily ration of D. theta was 1.5% of the weight of fish in the summer period and 3.2% in the autumn period.     

Estuarine Typology and the Structuring of Fish Communities in South Africa

Synopsis Some 190 South African estuaries, covering all biogeographic provinces within the region, were classified into three types based on a combination of mouth condition and estuary size (surface area). The fish communities of the estuary types within each zoogeographic region were described and compared. Multivariate analyses revealed that each estuary type contained somewhat distinct fish communities. In addition, the study identified common patterns in species richness and ichthyofaunal composition. Open estuaries have relatively high species richness; this is a reflection of a permanent or near-permanent connection with the sea which allows access into these estuaries by all marine migrant species within the region. Intermittent connection with the sea limits the recruitment and utilisation of closed estuaries by marine migrant species; this results in reduced species richness in moderate to large closed estuaries. Small closed estuaries exhibit the lowest species richness and this is probably a result of their limited habitat and increased isolation from the sea. The key fishes that utilise estuaries could also be categorised into a number of groups based on their relative importance within each estuary type. Some species are largely restricted to predominantly open systems. Other taxa, while important in predominantly open estuaries, also occur in moderate to large closed systems. Some estuarine-associated species are well represented in all estuary types but exhibit a greater importance in closed estuaries. This study has shown that South African fish communities not only reflect estuarine typology but also respond to these differences in a consistent manner that spans all zoogeographic regions. The prevalence of similar patterns in other parts of the world suggests that estuarine typology is a major driver in the structuring of global estuarine fish communities.     

渤海南部半滑舌鳎的食性及摄食的季节性变化

本文研究了渤海南部半滑鳎的食性及其摄食的季节性变化,胃食物分析结果表明,半滑舌鳎为底栖生物食性鱼类,以虾类,蟹类,双壳类及部分中下层小型鱼类为主要食物,兼食一些多毛类,头足类,腹足类,棘皮动物及海葵,半滑舌鳎终年摄食,其摄食强度的周年变化不大,半滑舌鳎常年捕食鲜明鼓虾,日本鼓虾,口虾蛄,隆线强蟹及泥古隆背蟹等。夏季加强捕食小刀蛏,凸壳肌蛤等双壳类,降春季外还捕食一些以虾虎鱼为主的中下层小型鱼类。     

胶州湾海水、海洋生物体中重金属含量的研究

研究了胶州湾海水、海洋生物体中重金属含量.结果表明,沿岸河口地区海水中重金属污染主要受沿岸工业排放废水的影响;海洋生物体内重金属含量不仅受海水中的重金属含量大小的支配,温度对其也有一定的影响.海洋生物体中重金属含量为底栖生物大于鱼类,以沉积物为主要饵料的杂食性底栖动物内重金属含量大于鱼类;海洋生物对于Cu比其它重金属具有较强的富集能力.     

胶州湾海水,海洋生物体中重金属含量的研究

研究了胶州湾海水、海洋生物体中重金属含量 .结果表明 ,沿岸河口地区海水中重金属污染主要受沿岸工业排放废水的影响 ;海洋生物体内重金属含量不仅受海水中的重金属含量大小的支配 ,温度对其也有一定的影响 .海洋生物体中重金属含量为底栖生物大于鱼类 ,以沉积物为主要饵料的杂食性底栖动物内重金属含量大于鱼类 ;海洋生物对于Cu比其它重金属具有较强的富集能力 .     

The population structure and growth of juvenile Rhabdosargus holubi (Steindachner) (Teleostei: Sparidae) in a closed estuary

The population structure and growth rate of Rhabdosargus holubi (Steindachner) in the closed West Kleinemond estuary in south east Africa, from 1971–973, are described. Juvenile R. holubi invade the estuary at a length of 1–2 cm but migrate back to the sea at a length of about 14 cm without attaining maturity in the estuary. Adult R. holubi are rarely encountered in estuaries. The annual growth increment of O group R. holubi was 6 cm, almost all occurring in summer. The growth of Lithognathus lithognathus (Cuvier) was also measured in the same closed estuary and O group fish of this species also grew 6 cm per annum although 1 + fish grew 8 cm per annum.     

Does reduced feeding prior to release improve the marine migration of hatchery brown trout Salmo trutta smolts?

The aim of this study was to test the hypothesis that hatchery brown trout Salmo trutta smolts, with 50% reduced or no feeding over the last 5 months before release, were more likely to migrate to the sea than individuals with standard feeding ratios. The juvenile fish were divided into three groups 176 days before release: (A) with no feeding, (B) with 50% and (C) with 100% feeding. To study their seaward migration, 40 fish from each feeding group were tagged with acoustic transmitters and tracked by automatic listening stations in the River Nidelva, Trondheim, Norway, its estuary and in the nearest marine environment. At the time of release, mean condition factor was significantly lower in group A and the fish from groups A and B had higher levels of Na+, K+‐ATPase. Significantly more fish from group A migrated to the sea, but the rate of downstream progression from release to the estuary did not differ between the three groups. In conclusion, the S. trutta smolts with no access to food in the last 176 day before release were more likely to migrate to the sea. Fish from all three feeding groups, however, appeared to smoltify and had the same rate of downstream progression to the estuary. This indicates that differences in migratory behaviour between individuals from the three feeding groups begin from the time when the fish reach saline waters. It is suggested that feeding in hatcheries has to be greatly reduced (by 50% or more) over several months to have a pronounced effect on the migratory behaviour in S. trutta.     

The mysid-feeding guild of demersal fishes in the brackish zone of the Westerschelde estuary

The demersal fish fauna of the mesohaline zone of the Westerschelde estuary (south-west Netherlands) was sampled intensively in the period 1990–1992. Almost 500 beam trawl samples were taken in both subtidal (330 samples) and intertidal (144 samples) habitats. These yielded 44 fish species, mostly as juveniles. The area functioned as a nursery for several demersal fish species, and harboured large populations of hyperbenthic mysids. Three gobies, three flatfish, one clupeoid and one gadoid dominated the fish fauna, while three mysid species were important components of the holohyperbenthos. From c. 1500 stomach contents of 25 fish species, 44 prey species were identified, the most abundant of which were also common in the hyperbenthal. The demersal fish community consisted of a group that foraged subtidally on fast-moving epi-and hyperbenthic prey (for example gadoids, gobies and clupeoids) and a group that foraged on slow-moving or sessile endobenthic organisms, mainly in intertidal areas (for example most flatfish species). Mysidacea occurred in >50% stomachs analysed and were taken as prey by 19 of the 25 fish species. Mysids were most important in the diets of Pomatoschistus minutus, P. lozanoi, Trisopterus luscus and Merlangius merlangus, and were present in appreciable numbers in Pleuronectes flesus, Trigla lucerna, Clupea harengus and Pleuronectes platessa. These species fed mainly on the brackish water endemic Neomysis integer. Mesopodopsis slabberi (present in 35% of the gobiid stomachs) and Gastrosaccus spinifer(present in 25% of the gadoid stomachs) were of secondary importance. P. minutus and T. luscus showed a diet shift from calanoids (Eurytemora aYnis and Temora longicornis) to mysids at L_S of 30 and 50 mm, respectively. Only 1% of the standing stocks of the N. integer and M. slabberi populations was removed by the local demersal fish community, so top–down control of mysid populations in estuaries seems unlikely.     

Strategies of resource partitioning between two sympatric puffer fishes in a tropical hypersaline estuary,Brazil

The strategies of food partitioning among two abundant estuarine puffer fishes, Sphoeroides greeleyi (Gilbert, 1900) and Sphoeroides testudineus (Linnaeus, 1758), were investigated in a tropical hypersaline estuary. We examined the stomachs of 946 fishes collected with a beach seine across three zones (upper, middle and lower estuary) along with a salinity gradient. The highest abundances of species were recorded in the upper and middle estuary. The diet was comprised mostly by benthic organisms, mainly Bivalvia, Gastropoda, and Brachyura. However, in a hypersaline estuary, these species develop strategies of resource partitioning in three ways: 1) asymmetry effects; 2) habitat selection; and 3) trade-offs among age classes. Diet variations according to fish age classes indicated that the largest individuals showed a decrease in their consumption of small preys (Amphipods, Copepods, and Ceratopogonidae) and an increase in their consumption of larger preys (Bivalvia and Decapoda). This behavior of switching diet towards larger prey was related to the functional trade-offs in swimming capacity, and feeding mode used to capture prey. The middle and upper estuary are important feeding grounds for puffer fishes, as demonstrated by their influence on prey distributions and habitat type. Diet breadth indicated that S. greeleyi tended to be a generalist, whereas S. testudineus tended to be a specialist. Thus, the strategies of partitioning seem to have importance for puffer fish populations in this hypersaline environment.     

Trade-offs between ontogenetic changes and food consumption in Brazilian silverside Atherinella brasiliensis from two tropical estuaries

Salinity variation in estuarine environments influences the distribution of fish species as well as the availability of food resources to be used by them. This study examines the effect of the range of salinity on the trade-off between growth and feeding intensity of Atherinella brasiliensis from two tropical estuaries (positive and hypersaline). To investigate the effects of salinity, we hypothesized that hypersalinity negatively affects foraging intensity, consumption and prey selection by the Brazilian silverside, leading to differences in body condition. Sampling was carried out using the beach seine method in two areas of the estuaries (upper and lower zone) during rainy and dry periods. A total of 2549 stomachs (1124 for the positive estuary and 1425 for the hypersaline estuary) were examined, and the results indicated a dissimilarity of 92.7% of the diet between environments. In the positive estuary, there was more predation on Calanoida, Gastropoda, Hymenoptera, Ceratopogonidae larvae and Decapoda larvae, while Alga and plant-material characterized the diet in the hypersaline estuary. Significant correlations between the volume of food and salinity were observed in both estuaries. The vacuity index indicated that hypersaline environments presented higher contributions of semifull stomachs, indicating an intense consumption of algae. On the other hand,in the positive estuary, these values were less intense, but the stomachs were always with animal items. The variation found for both environments reinforces the effect of salinity on the physiological mechanism of the populations once the higher proportions of filled stomachs in the hypersaline environment indicate the need for constant and high ingestion of prey to guarantee the pronounced energy expenditure with osmoregulation.     

The diet of Brycinus nurse (Pisces: Characidae) from Asa reservoir,Ilorin, Nigeria

From November 1991 to October 1993, 980 specimens of the characid Brycinus nurse were collected from Asa reservoir to examine its diet. The diet was analyzed using the frequency of occurrence, numerical and gravimetric methods. Two hundred and sixty nine (27.45%) of the stomachs examined were empty. The fish was an omnivore feeding extensively on a wide array of plant and animal food items. These consisted of 9 families, 10 genera and 10 species. The most extensively consumed plant food item was aquatic plant parts which occurred in 63.88% of the stomachs, and accounted for 6.06% by number and 12.10% by weight while the ephemeropteran, Povilla adusta was the most dominant animal food item, occurring in 50.92% of the stomachs, and accounting for 11.98% by number and 11.86% by weight. Conversely, the least consumed plant food item was Volvox occurring in 4.49% of the stomachs and accounting for 0.18% by number and 0.35% by weight, while the fish Barbus sp. was the least consumed animal food item occurring in 0.51% of the stomachs, accounting for 0.03% by number and 1.62% by weight. New food items not previously recorded such as a watermite. Aspatharia sinuata and Barbus callipterus were found in the stomach contents. The nonspecific feeding regime of the fish and its ability to utilize different food items effectively was what accounted for the prominence and wide distribution of the fish in the lake.