Variation In Feeding Intensity Research Articles

Feeding ecology of the pandalid shrimp, Plesionika semilaevis (Spence Bate 1888) in South Eastern Arabian Sea

The feeding ecology of deep-sea crustaceans is crucial in understanding the ecological roles and interactions of deep-sea organisms as they play a critical role in deep-sea food webs as intermediate trophic level organisms. This study provides the first examination of the feeding ecology of deep-sea shrimp Plesionika semilaevis (Spence Bate 1888) and provides new insights into deep-sea community structure. An aggregate number of 2213 individuals (842 males, 1016 berried and 355 non-berried females) were collected from the South Eastern Arabian Sea from 2019 to 2022 and their feeding ecology was studied in relation to the environmental (season) and biological (maturity, sex and size) factors. The index of preponderance values indicates the species has a diversified diet with a wide trophic niche ranging from smaller foraminifera to larger crustaceans and fishes. Frequency of occurrence (FOC) reveals that crustaceans, detritus and foraminifera forms the main prey while fishes, molluscs and sponges form the secondary prey. Berried females had the highest feeding intensity compared to males and non-berried females. Among the studied groups,the percentage of full stomachs was higher during the pre-monsoon period than post-monsoon. Feeding intensity was highest for smaller individuals and decreased gradually with an increase in size. Statistical analyses (ANOVA) also confirmed the significant differences (p<0.05) in the diet composition and feeding intensity of berried and non-berried females, pre-monsoon and post-monsoon samples and, juveniles and adults. The PERMANOVA test showed that there were significant differences in diet in the interaction between sex and size (p=0.003) and between sex and season (p=0.001). The present study also suggests that the seasonal variation in feeding intensity could be attributed to oceanographic phenomena like upwelling prevailing in the South Eastern Arabian Sea.

Diet components, dietary habits, resource and its use in the coexisting catfish species

In over last six decades fisheries of the Ganga river System in general and the Ganga R. in particular have witnessed a radical change in dominance from the carp to catfish and now to invasive exotic species. Has this happened due modified river environment (natural flows, pollution) or have the species modified the food-web of the river is an issue that should be addressed in deep earnest intent. Among many facets that need to be answered, we should know the food resources base available in the river environment, preferences of fish species, if it is selective and the extent of overlap among the sympatric and co-existing species. The present investigation precisely examines this for the co-existing catfish species, Rita rita and Bagarius bagarius. R. rita feeds with greater intensity than B. bagarius. In R. rita intensity was high in pre-monsoon (January to May) compared to B. bagarius where intensity was higher in post monsoon (October to December). R. rita showed +ve preference for chironomid-Diptera and variety of Trichoptera among insects.Others include crustaceans and gastropod molluscs. In contrast B. bagarius shows preferences for a consortium of Diptera (Simuliidae), Trichoptera (Glossosomatidae), Ephemeroptera (Heptageniidae), Coleoptera and Odonata among insect food. It has high preference for fish elements. Both species select these items. There is a biologically significant diet overlap but these species avoid competition not only by selecting different items from the common food resource base but also by seasonal variation in feeding intensity. Such studies need to be extended to fish within and among feeding guilds. Keywords Catfish, diet composition, co-existance

The Relative Gut Length and Gastro-somaticindexes of the Mudskipper Periophthalmodon septemradiatus (Hamilton, 1822) from the HauRiver

This study provided an understanding of feeding habit and intensity of the mudskipper Periophthalmodon septemradiatus, which was a potential aquarium pet, by analyzing the relative gut length (RGL) andgastro-somatic (GaSI) indexes. Fish specimens were caught by fishing rods from the estuary in Soc Trang province to the upstream in An Giang province of Hau River during a period of one year from August 2017 to July 2018. Data analysis of a collection of 1,504 fishes showed that RGL did not change with fish size, resulting in the feeding habit of P. septemradiatus did not change with fish size. By contrast, the feeding habit of this mudskipper varied with place, month and season as the RGL significantly different between place, month and season, but both males and females fall into carnivorous fish as RGL was &lt;1. Similarly, the feeding intensity of this specice did not change with fish size, as the GaSI was not significantly different among four fish size groups. Meanwhile, the mudskipper displayed spatial, temporal and seasonal variations in feeding intensity since GaSI significantly changed with place, month and season. The changes of feeding habit and intensity of P. Septemradiatus were not regulated by the interaction of fish size and place, fish size and season, and place and season. These results provided new knowledge on feeding habit and intensity of this fish specice, being used for the understanding of fish adaption and conservation in the study region.&#x0D; Keywords&#x0D; Gastro-somatic index, mudskipper, Periophthalmodon septemradiatus, relative gut length&#x0D; References&#x0D; [1] Murdy, E. O. &amp; Jaafar, Z., Taxonomy and systematics review, In: Z. Jaafar, E. O. Murdy (eds) Fishes out of water: biology and ecology of mudskippers, CRC Press, Boca Raton, pp. 1-36, 2017 [2] Murdy, E. O., A taxonomic revision and cladistic analysis of the oxudercine gobies (Gobiidae, Oxudercinae), Australian Museum Journal, 11 (1989) 93.[3] Murdy, E., Systematics of Oxudercinae, In: R. A. Patzner, J. L. V. Tassell, M. Kovacic, B. G. Kapoor (eds) The biology of gobies, Science Publishers, New Hampshire, United States, pp. 99-106, 2011 [4] Bhatt, N. Y., Patel, S. J., Patel, D. A. &amp; Patel, H. P., Burrowing activities of goby fish in the recent intertidal mud flats along the Navinal coast, Kachchh, Western India, Journal of the Geological Society of India, 74 (2009) 515-530.[5] Al-Hussaini, A. H., On the functional morphology of the alimentary tract of some fish in relation to differences in their feeding habits: anatomy and histology, Quarterly Journal of Microscopical Science, 3 (1949) 109-139.[6] Desai, V. R., Studies on fishery and biology of Tor tor (Hamilton) from river Narmada. I. Food and feeding habits, Journal of the Inland Fisheries Society of India, 2 (1970) 101-112.[7] Le, T., Nguyen, M. T., Nguyen, V. P., Nguyen, D. C., Pham, X. H., Nguyen, T. S., Hoang, V. C., Hoang, P. L., Le, H. &amp; Dao, N. C., Provinces and City in the Mekong Delta, Education Publishing House, Ha Noi, 2006.[8] Khaironizam, M. Z. &amp; Norma-Rashid, Y., First record of the mudskipper, Periophthalmodon septemradiatus (Hamilton) (Teleostei: Gobiidae) from Peninsular Malaysia, Raffles Bulletin of Zoology, 51 (2003) 97-100.[9] Wand, M. P., Data-based choice of histogram bin width, The American Statistician, 51 (1997) 59-64.[10] Vo, T. T. &amp; Tran, D. D., Study on nutritional characteristics of Oxyeleotris urophthalmus fish distributed along the Hau River, Can Tho University Journal of Science, Fishery (2014) 192-197.[11] Dinh, Q. M., Nguyen, D. T. &amp; Danh, S., Food and feeding habits of the broadheah sleeper Eleotris melanosoma from coastline in Soc Trang, Proceedings of the 7th National Scientific Conference on Ecology and Biological Resources, Publishing house for Science and Technology, 1873-1879, 2017.[12] Tran, D. D., Some aspects of biology and population dynamics of the goby Pseudapocryptes elongatus (Cuvier, 1816) in the Mekong Delta, PhD thesis, Universiti Malaysia Terengganu, 2008.[13] Dinh, Q. M., Qin, J. G., Dittmann, S. &amp; Tran, D. D., Seasonal variation of food and feeding in burrowing goby Parapocryptes serperaster (Gobiidae) at different body sizes, Ichthyological Research, 64 (2017) 179-189.[14] Dinh, Q. M. &amp; Tran, M. T. D., Digestive tract morphology, food and feeding habits of the goby Stigmatogobius pleurostigma (Bleeker, 1849) from the Coastline in Soc Trang, VNU Journal of Science: Natural Sciences and Technology, 34 (2018) 46-55.&#x0D;

Reproductive biology, diet and feeding pattern of longtail tuna Thunnus tonggol (Bleeker, 1851) in the north-eastern Arabian Sea off Gujarat, India

Longtail tuna &lt;em&gt;Thunnus tonggol&lt;/em&gt; (Bleeker, 1851) is the major tuna resource in the neritic realms of the northern Arabian Sea and forms considerable fishery in the coastal nations in the region. Gujarat, on the north-west coast is the major province landing longtail tuna in India. The paper attempts to add to the hitherto sparse knowledge base on biology of the longtail tuna fished along the north-west coast of India, through a study spanning from 2011 to 2015. Reproductive biology, spawning, food and feeding dynamisms of the species were investigated. Sex ratio of the species was estimated as 1:2.1 and depicted an increase in male preponderance as the size increased. The fish attains maturity at 607 mm and it spawns during summer months starting from May. The fish is typically a non-selective feeder and over 22 taxa comprising of fishes, cephalopods and crustaceans formed the diet at varying rates over the year. Variation in feeding intensity at different reproductive stages is discussed besides the constraint posed by the large presence of unidentifiable, partially digested gut content.

Food and Feeding Habits of the Deep-Water Mud Shrimp (Solenocera melantho) of Visakhapatnam Coast, India

The food and feeding habits of the shrimp Solenocera melantho off Visakhapatnam coast were studied qualitatively and quantitatively. Feeding intensity differs in relation to gender, size, season and stage of maturity. Detritus was the major component of the food consumed, followed by crustaceans, molluscs, foraminiferans, fish remains, eggs; sand was also found as one of the gut contents. Diet preference in males and females was similar, but varied with size and season. The index of preponderance of detritus was 50.88% in males and 47.16% in females. Variation in feeding intensity was noticed in relation to size, months and season. The overall feeding intensity in males and females was categorized as actively fed (21.52% and 40.78% respectively), moderately fed (22.07%, 19.72%) and poorly fed (14.07%, 27.03%) respectively. S. melantho may designate as an omnivorous detritivore with scavenging activity.

The feeding ecology of schilbeid catfishes in river Ase, Niger delta, Southern Nigeria.

The feeding ecology of Parailia pellucida (Boulenger, 1901), Eutropius niloticus (Rϋppel, 1872) and Schilbe mystus (Linnaeus, 1756) were investigated for two years (March, 1982-February, 1984) in River Ase, Niger Delta, southern Nigeria. A cyclic pattern of fish sampling was used and fish samples were collected from 0600-0900, 0900-1200, 1200-1500, 1500-1800, 1800-2100, 2100-2400, 2400-0300, 0300-0600 (hrs) using various fishing gear. Percentage food items and condition factors (kf) were calculated for each species. Feeding habits in relation to size groups, diel and monthly variations in feeding intensity were described for Eutropius niloticus and Schilbe mystus which had adequate data. The three species P. pellucida, E. niloticus and S. mystus were omnivorous surface feeders. They consumed more food items in the dry season than during the rainy season. Diel variations in feeding habit occurred both day and night with higher intensity at night especially between the hours of 9p.m. and 12 midnight. S. mystus is both day and night feeder. The medium size group of E. niloticus consumed a wider variety of food items than the small and large size groups. S. mystus consumed almost the same food items in both dry and rainy seasons. In the three size groups, most food items were selectively consumed indicating gape size as a limiting factor. The condition factors (kf) of the three species were above 1 indicating well being. Some aspects of the feeding ecology of the three schilbeid catfishes have been discussed and the results compared with the results of earlier investigations conducted elsewhere. Key words : schilbeidae, feeding ecology, diel variation, seasonality

The survival of Pacific salmon in the North Pacific in the winter and spring

The effects of various factors (water temperature, food availability, predation, and the size of juveniles) on the survival of Pacific salmons during overwintering in open ocean waters are analyzed based on the data collected by expeditions of the Pacific Research Fisheries Center to the northwestern Pacific Ocean in the winter and spring seasons of 1986–1992 and 2009–2011, as well as in the summer seasons of 2004–2011. The temperature factor is unlikely to be a direct cause of the high salmon mortality in the ocean during the winter, as there is no clear evidence that it affects food availability for salmon. The biomass of forage zooplankton in the Subarctic Front zone in February and March is lower than that in April and June–July, but it does not decrease substantially in the winter months. Taking the fact into account that the total abundance of planktivorous nekton is also low in this area during the winter, food availability cannot be considered a crucial factor that has a serious influence on salmon mortality in this period. The difference in feeding intensity between salmon species and between their size groups in the winter and spring is determined by their life strategies. The observed variations in feeding intensity and lipid accumulation from autumn to spring are caused by cyclic seasonal changes in physiological processes in salmon rather than by the amount and availability of food resources. The low abundance of predators in subarctic waters and in the Subarctic Front zone in the winter also cannot reduce salmon abundance substantially. The probable relationship between the critical size of juveniles and their survival in the winter is considered using the example of a Sea of Okhotsk stock of pink salmon. The conclusion is that the size of juvenile pink salmon cannot always be used as a predictor of the values of its subsequent returns, because survival of salmon during the ocean period of life depends both on the initial conditions during downstream migration and on the ocean conditions that form in the winter. Thus, none of the factors above can be considered as strictly limiting the abundance of Pacific salmon in the winter. It is more probable that the survival of salmon in the ocean is influenced, to a lesser or greater extent, by the combined effects of abiotic and biotic factors.

Evaluation of feeding indices of cobia Rachycentron canadum (Linnaeus. 1766) from Northwest coast of India

Cobia Rachycentron canadum (Linnaeus. 1766) is an esteemed table fish occurring along both east and west coast of India. Feeding indices of the species inhabiting waters of the northwest coast of Indian EEZ was studied to understand the variation of its feeding intensity based on season, sex and life history changes. Monthly variation of stomach condition of cobia male, female, pooled and size wise were analyzed. In general, 56% of fishes were found in either actively fed or moderately fed state. Except during April and July they were found in actively fed condition. Analysis of occurrence of empty stomach in different length classes of fishes revealed that the percentage of occurrence of empty stomachs decreased with the fish growth. Month- wise Mean Index of Feeding intensity (MIF) and Index of Fullness (IF) values showed that cobia fed well during post monsoon periods but poor feeding activity was noticed in July. Gastrosomatic index for male, female and pooled samples of matched with the MIF and IF values. The results indicated a seasonal variation in feeding intensity of cobia. On an average, feeding intensity during July was low.

Reproduction and feeding habits of the River Catfish Eutropiichthys vacha (Hamilton, 1822) (Siluriformes, Schilbidae) in an impacted habitat: Kotri hydrodam, River Indus, Pakistan

Reproduction and feeding habits of Eutropiichthys vacha were studied in Kotri hydrodam, a man-made and human impacted stretch of the Indus River, Pakistan during 2005-2006. A total 303 specimens were sampled and analyzed for maturity stages and gonadal development and food and feeding habits assessed from gut contents. Results showed male dominance over females: sex ratio 1.16:1.0. Minimum size at sexual maturity was 13.9 cm total length (TL). Mean fecundity ranged 1.38x104 to 2.17 x 105. Gonado-somatic index (GSI) was 0.1-2.5 and 0.3-6.5 for males and females, respectively. Highest GSIs were recorded in April. We observe an ontogenic dietary shift in E. vacha: young are omnivorous with insects dominating diet while adults are omni-piscivores with Puntius ticto accounting for 35.4% of species. Other species were Colisa spp., juveniles of Channa spp. and some cyprinids. Feeding intensities were lowest in April at peak of spawning. The intensities increase rapidly after spawning indicating voracious feeding in E. vacha. Feeding intensities in adults are low during the cold season. These results provide for assessment of spatial-temporal variations in feeding intensity in E. vacha while GaSI and diet composition reveal information on environmental shifts and ecosystem fluctuations in the impacted habitats of the River Indus for sound fisheries management.DOI: http://dx.doi.org/10.3126/on.v10i1.7795

Trophic ecology of three dominant myctophid species in the northern California Current region

The feeding ecology of 3 dominant sympatric myctophid species (Tarletonbeania crenu- laris, Diaphus theta, and Stenobrachius leucopsarus) in the northern California Current System was investigated based on samples collected in June, August, and September of 2006. All 3 species fed predominantly on Euphausia pacifica, the most abundant euphausiid off the central Oregon coast. In contrast, the same 3 lanternfishes showed marked variation in utilization of other principal food categories, and stronger resource partitioning was evident in smaller individuals. The proportion of euphausiids in the diet of T. crenularis and S. leucopsarus gradually increased with increasing size. D. theta at intermediate sizes (31 to 60 mm) preyed heavily upon salps and hyperiid amphipods, whereas the largest specimens consumed mostly euphausiids. S. leucopsarus showed little changes in composition of principal food categories between months, while T. crenularis and D. theta consumed more hyperiid amphipods in June, euphausiids in August, and salps in September. No feeding on salps was recorded in S. leucopsarus for the entire study period. All 3 species showed variation in feeding intensity, stomach fullness, state of digestion, and number of prey species and prey items per stomach. A divergence in feeding strategies of these co-occurring lanternfishes appears to reflect their structural morphology and generally conforms to an ecological subdivision of this midwater family into 'active' and 'inactive' species. Active myctophids (T. crenularis and D. theta) consumed significantly larger amounts of protein-rich prey such as euphausiids, hyperiid amphipods, and salps, while inactive S. leucopsarus showed higher preference for slower-moving, lipid-rich Neocalanus copepods.

Horse mackerel (Trachurus trachurus) stomach fullness off Portugal: index calibration and spatio-temporal variations in feeding intensity

Abstract Garrido, S., Murta, A. G., Moreira, A., Ferreira, M. J., and Angélico, M. M. 2008. Horse mackerel (Trachurus trachurus) stomach fullness off Portugal: index calibration and spatio-temporal variations in feeding intensity. – ICES Journal of Marine Science, 65: 1662–1669. An index for stomach fullness used in the routine biological sampling of horse mackerel from Portuguese waters was calibrated about the correspondent stomach mass. The fullness scale comprises four levels (1, empty; 2, &lt;50% filled; 3, &gt;50% filled; 4, bursting) that are easily attributed to whole stomachs during the sampling process. Significant differences were found among the four levels of the fullness scale in their relative stomach masses, indicating that the index can be used for the semi-quantitative analysis of feeding intensity in this species. The fullness index was applied to study spatio-temporal variations in horse mackerel feeding off the Portuguese coast, using data collected from 1985 to 2006 on commercial vessels and research cruises. There was no significant difference in feeding intensity between sexes. Smaller horse mackerel and those in the resting stage of reproduction fed more intensively than larger and spawning fish. Feeding intensities of fish from the southern and northwest coasts of Portugal were greater than for those captured along the southwest coast. Horse mackerel feeding intensity was greater at dawn and varied seasonally, being higher during spring and autumn and lower during winter. Interannual variation in feeding intensity of horse mackerel captured along the west coast of Portugal revealed a significant but slight decrease in recent years.

Disproportionate Relative Importance of a Terrestrial Beetle Family (Coleoptera: Scarabaeidae) as a Prey Source for Central Appalachian Brook Trout

AbstractBrook trout Salvelinus fontinalis and other salmonids in Appalachia typically inhabit headwater watersheds, where food resources may limit growth. We monitored the feeding trends of a brook trout population in central Appalachia over the course of 2 years to determine variation in feeding intensity and important prey items. One terrestrial beetle family, Scarabaeidae, provided a disproportionate amount of energy during the only time of year when brook trout were feeding substantially above maintenance ration. Scarab beetles contributed 39.6% of all energy consumed during May and June of both years, though the number of fish with one or more scarabaeids present in the stomach varied by month (22.2–51.7%). The species composition of scarab beetles consumed suggested that four species are of particular importance. Our findings imply that scarabaeids represent a considerably important prey taxon for brook trout in the region. Considering the foraging habits of the scarabaeid species in question, the phenomenon we witnessed probably occurs throughout Appalachia.

The feeding ecology of mochokid species in River Ase, Niger Delta, Nigeria

The feeding ecology of fifteen mochokid species ( Brachysnodontis batensoda, Hemisynodontis membranaceous, Synodontis budgetti, S. omias, S. clarias, S. resupinatus, S. sorex, S. eupterus, S. nigrita, S. ocellifer, S. schall, Synodontis gambiensis, S. violaceous, S. vermiculatus, S. courteti ) in River Ase, Niger Delta, Nigeria was studied for two years. Monthly mean condition factors (kf) for all species were above one (1) indicating well being throughout the study period. Feeding habits in relation to three sized groups, diel and monthly variations in feeding intensity were described for Synodontis schall due to adequate data. S. schall fed both day and night but with higher feeding intensity at night. On monthly basis, feeding intensity was highest in December. There was no significant difference (P>0.05) between food items consumed during the dry and rainy seasons. All the fish species fed on various food items with detritus being the most prominent food item by consumed by many species. The feeding ecology of mochokid species has been discussed. Keywords : feeding ecology, mochokid species, Niger Delta Tropical Freshwater Biology Vol. 14 2005: 71-93

The feeding ecology of bagrid species in River Ase, Niger Delta, southern Nigeria

The feeding ecology of seven bagrid species was studied between March, 1982 and February, 1984. A summary of the food items and condition factors (kf) in relation to sized groups were described for all the seven species while feeding intensity are to sized groups, diel and monthly variations in feeding intensity are provided only for Chrysichthys auratus longifilis (Geoffrey St. Hilaire, 1908) and C. nigrodigitatus (Lacepede 1803) due to data. Variations in food items between dry and rainy seasons were not remarkably different. There were differences in the feeding habits of different sized groups in C. auratus longifilis while in C. nigrodigitatus, all the sized groups consumed mainly detritus. Both C. auratus longifilis and C. nigrodigitatus fed both day and night. Feeding intensity was highest in C. auratus longifilis from 2100 to 2400 (h) and from 2400 to 0300(h) for C. nigrodigitatus. Based on the food items, Bagrus bayad macropterus Pfaff, 1933 was mainly piscivorous in diet while B. domac niger Daget, 1954 fed on fish and decapod crustaceans. C. auratus, C. nigrodigitatus, C. furcatus (Gunther, 1864) and Auchenoglanis occidentalis (Cuvier and Valencienness, 1840) were omnivorous bottom feeders. Clarotes laticeps fed on fish and detritus. The feeding ecology of bagrid species has been discussed and compared with the findings of earlier studies conducted elsewhere. Key Words: Bagridae, feeding ecology, Niger Delta, diets, seasonality Tropical Freshwater Biology 11 (2002) 47-68

Marine feeding of anadromousSalmo truttaduring winter

Juvenile and adult anadromous troutSalmo truttautilize the sea for feeding during the winter in the Skagerrak. This finding conflicts with the traditional view that anadromous trout overwinter in fresh water. Adults, just prior to spawning, were captured at sea in October to December, and spent fish were caught at sea from October to April, showing that the fish may leave the stream and move to sea just after spawning and spend the winter there. During mid‐winter (January to February), the feeding probability (chance of finding a fish with food in its stomach) increased markedly with increasing body length, with no similar effect during early and late winter (October to December and March to April). Among individuals with food in their stomach (72·5%), there was no evidence for variation in feeding intensity [stomach fullness = (mass of stomach content)(fish body mass)−1] among early, mid‐, and late winter.

The Ecology and Conservation of European Smelt (&lt;i&gt;Osmerus eperlanus&lt;/i&gt; L.) from Waterford Estuary, in Southeastern Ireland

The smelt (Osmerus eperlanus L.) is a little-known indigenous fish species in Ireland. All known Irish populations are anadromous. A total of 173 smelt were captured using a variety of fishing methods in Waterford Estuary over the period June 1997 � /June 1998. Analyses of the stomach contents revealed that they fed almost exclusively upon the marine mysid Praunus neglectus and other macroinvertebrates such as Hyperia galba and Crangon allmani. Piscivorous feeding, including cannibalism, was also evident, and three fish species were recorded in the smelt stomach contents (Merlangus merlangus, Sprattus sprattus and Osmerus eperlanus). Seasonal variation in feeding intensity was also noted. Six metazoan parasite species were recorded from the Waterford Estuary smelt. These included two digeneans (Diplostomum spathaceum and D. gasterostei), one cestode (Proteocephalus longicollis), two nematodes (Hysterthylacium aduncum and Anisakinae sp.) and one ectoparasitic crustacean species (Caligus eperlanus). Parasite prevalences and mean intensities of infection were recorded. The smelt examined ranged from 1� /to 5� /years, with the majority belonging to the 2� /and 3� /cohorts. They varied in size (125 � /260mm fork length) and in weight (15 � /129g). Their growth rates were broadly similar to those of smelt populations elsewhere in Europe. Maturation of gonads and increasing egg diameter in ovaries of female smelt in the Waterford Estuary were noted prior to a spring spawning period. No clear correlations were found for either mean egg diameter or fecundity when parental body size or age were taken into account. However, this may be due to the relatively small sample size.

Tracing the life history of red gurnard (Aspitrigla cuculus ) using validated otolith annual rings

Back calculation, marginal increment analysis and modal progression analysis were used to trace growth processes of the red gurnard, Aspitrigla cuculus L., in the Mediterranean Sea. Three false rings appeared regularly on otoliths and were hypothesized to refer to the ontogeny on the basis of the study of the recruitment and reproduction processes of the species. The first two rings were laid down during the first pelagic period and the transformation to the bottom mode of life, respectively. The third ring corresponded to the first spawning at the end of the second year of life. The marginal increment analysis demonstrated that one opaque and one translucent zone is formed each year, the translucent ring corresponding to the period of slow growth in the winter. Temperature and salinity of Mediterranean waters below the thermocline where red gurnard live do not undergo seasonal variations. Therefore, traditional interpretation of the discontinuity patterns on otoliths related to the decrease of water temperature should be rejected for Mediterranean fish distributed on the deep shelf and slope. Discontinuities in otolith structure may be related to seasonal variation in feeding intensity as a consequence of decreases in the benthic mysids biomass and time available to find food due to reduced daylight. Future research should focus on the trophic ecology of the demersal fishes and the seasonal fluctuations of the prey resources during the year in order to assess the role of the food supply with regard to otolith growth patterns in the Mediterranean Sea.

The abundance and trophic biology of Clarias albopunctatus Nichols & LaMonte, 1953 (Osteichthyes: Clariidae) in a tropical floodriver basin

The abundance, food and feeding biology of Clarias albopunctatus was studied over a period of 17 months in the lower River Anambra, Nigeria. The catfish was more abundant in late dry season (January–March) and early rainy season (April–June) than in other periods of the year in the small-sized Akwu pond than in other habitats. Feeding intensity was higher at night and at dawn (20.00–05.00 h) than during the day (08.00–17.00 h) in the 151–200 mm TL size class and during the rainy season (April–September). There was no sex-dependent variation in feeding intensity. Insects were the predominant food, followed by crustaceans. Of primary importance were Chironomidae (mainly Chironomus spp. and Tanypus sp.), Odonata nymphs, Dytiscus sp., mosquito larvae and pupae, Gyrinus sp., Daphnia sp., Ostracoda and Tilapia fry. Qualitative food composition and food richness were size, but not sex – or season-dependent. Diet breadth increased with catfish size and during the rainy season. The feeding behaviour of the catfish include foraging, shovelling and surface feeding. Abundant food and ability to switch to more available items enable C. albopunctatus to maintain its abundance in the River Anambra.

European hake Merluccius merluccius (L., 1758) feeding in the Cantabrian Sea: seasonal, bathymetric and length variations

In 1994, 5828 stomachs of European hake, Merluccius merluccius (L., 1758) were analysed on commercial trawl and gill-net vessels in the Cantabrian Sea (northern Spain). Data were analysed quantitatively using fullness indices, and differences in feeding intensity and diet composition were compared statistically by quarter, by depth strata, and throughout the predator length-range. The results show that feeding is more intense during the second quarter among specimens longer than 30 cm, which may be related to recovery from the spawning season. There was very little seasonal variation in diet composition, this being centred on blue whiting from 30 cm, as well as on horse mackerel Trachurus trachurus (L., 1758) and silvery pout Gadiculus argenteus (Guichenot, 1850) at shorter lengths. By depth, there was no noteworthy variation in feeding intensity, but an increase in the predominance of blue whiting was observed as depth increased, with a greater intake of horse mackerel and clupeids at less than 200 m. Regarding predation on blue whiting Micromesistius poutassou (Risso, 1826) in the Cantabrian Sea, there is apparently no selection of prey lengths, since length distributions in the stomachs closely coincided with those of the total catches of this species in the study area. Compared with another study conducted in the northern Bay of Biscay, the present findings show marked differences in the composition of this species's diet.

Feeding habits and diet in two populations of spined loach, Cobitis taenia (L.)

SUMMARY. The feeding habits of Cobitis taenia were studied by means of monthly samples taken over a 2‐year period, October 1972‐October 1974, from two sites, one on the River Great Ouse at Newport Pagnell and the other at some neighbouring gravel pits. Dietury components, seasonal variation in these components, and seasonal and diurnal variation in feeding intensity were examined. The ecological niche of the food items and their size range are discussed, since both these factors appeared important in governing the micro‐habitat of the fish.The feeding activity followed a seasonal cycle with little or no feeding in the winter and a high level of feeding activity in mid‐summer.The diet showed a predominance of small food items, such as chydorids. copepods and rhizopods. These items varied in occurrence during the feeding period which appeared to be related to their own abundance, pointing to non‐seleclive feeding by the fish. The small size and benthic habits of the food items, many of which are closely associated with surface layers of mud and weed, indicated a preference by Cobitis taenia (L.) for feeding in this type ot habitat and on this type of food, in contrast to the stone loach. Noemacheilus barbatulus (L.), which is believed to inhabit stony areas and take larger food items.