Gelatinous zooplankton (ctenophores,salps and medusae): an important food resource of fishes in the temperate SW Atlantic Ocean

This study quantifies the occurrence of gelatinous zooplankton in the stomach contents of fishes from the southwest Atlantic Ocean (33°–55°S). More than 69,000 fish stomachs belonging to 107 species were examined. A total of 39 fishes were documented as consumers of gelatinous zooplankton, 23 of which were newly discovered. Three gelatinous organism consumption categories are recognized: (1) very frequent consumers (10 species, six of which were exclusive); frequent consumers (five species); and occasional consumers (26 species). Three types of gelatinous prey (ctenophores, salps and medusae) were found in the stomach contents of fishes. Ctenophores were consumed at high levels across almost the entire continental shelves of Argentina and Uruguay. Salps were frequent prey on the slope and southern shelf. In contrast, medusae were consumed in coastal areas, slopes and the southern shelf. Classification methods (group average sorting of the Bray–Curtis similarity measures based on log (X?+?1)-transformed percentage data) determined six areas where fishes predated on gelatinous organisms. SIMPER (similarity percentages) analysis determined which fishes contributed more to the consumption of gelatinous organisms. Results revealed that two fish species (Stromateus brasiliensis and Squalus acanthias) had high gelatinous zooplankton predation rates throughout the entire study area, while another six species (Patagonotothen ramsayi, Helicolenus dactylopterus lahillei, Macrourus holotrachys, Merluccius hubbsi, Schroederichthys bivius, and Macruronus magellanicus), while widely distributed, seemed to have specific areas where consumption occurred. This study not only provides new knowledge about the importance of gelatinous zooplankton in the diet of numerous fishes, but might also be valuable for planning and managing local fisheries.     

From gelatinous to muscle food chain: rock cod Patagonotothen ramsayi recycles coelenterate and tunicate resources on the Patagonian Shelf

Stomach contents of 4808 fishes of 20 species caught in the eastern part of the Patagonian Shelf between 1999 and 2012 were analysed to assess dietary contributions of gelatinous plankton resources. Gelatinous plankton occurred in diets of seven species with two species, Patagonotothen ramsayi and Squalus acanthias, having >10% ctenophores in their diet. Consumption of gelatinous plankton was important in P. ramsayi and was strikingly seasonal, with maximum occurrence (up to 46% of non‐empty stomachs) in late summer to autumn. Ctenophores were most abundant in P. ramsayi of 25–34 cm total length, L_T, whereas salps were more frequent in larger >35 cm L_T individuals. In winter to spring, occurrence of gelatinous plankton in diets was minimal, reflecting their overall seasonal abundance in the ocean. The recent increase in abundance of P. ramsayi has enabled the species to recycle a significant proportion of the ecosystem production from gelatinous dead end to the main muscular food chain via seasonal reliance on ctenophores, jellyfish and tunicates. This additional influx of production that has been diverted from the gelatinous food chain favours the increase in abundance of several piscivorous top predators and affects the trophic web structure of the Patagonian Shelf ecosystem.     

Associations between gelatinous zooplankton and hyperiid amphipods (Crustacea: Peracarida) in the Gulf of California

Hydrobiologia - Hyperiid amphipods are pelagic crustaceans that live associated with gelatinous zooplankton including medusae, ctenophores, siphonophores, and salps. Standard plankton sampling...     

A review of cnidarians and ctenophores feeding on competitors in the plankton

Predation among pelagic cnidarians and ctenophores is reviewed. The diets of semaeostome scyphomedusae and hydromedusae commonly include other gelatinous zooplanktivores. However, few species of siphonophores and ctenophores are known to consume other gelatinous species. Most of these species can be said to exhibit intraguild predation, since they consume species that potentially compete with them for food. In addition, some hydromedusan and ctenophore species may consume other gelatinous zooplanktivores exclusively. Characteristics of cnidarians and ctenophores as predators and as prey of other gelatinous species are discussed.     

Associations between gelatinous zooplankton and hyperiid amphipods (Crustacea: Peracarida) in the Gulf of California

Hyperiid amphipods are pelagic crustaceans that live associated with gelatinous zooplankton including medusae, ctenophores, siphonophores, and salps. Standard plankton sampling disrupts natural associations, so the most reliable way to determine an association is through direct observation of the organisms in their environment. The planktonic fauna of the Gulf of California dwelling between 10 and 3000 m was surveyed using SCUBA diving and a remotely operated submersible (ROV) during March 2003. Here we report our observations on a total of 14 symbiotic associations found between the hyperiid amphipods and various taxa of gelatinous zooplankton. We found parental care behavior in a group of amphipods (Oxycephalidae) in which this phenomenon has not been previously reported. For two hyperiid species, Euthamneus rostratus and Vibilia australis, we present the first information on their symbiotic relations. Additional hosts were discovered for other well-known and widely distributed hyperiid species (i.e. Brachyscelus crusculum, Hyperoche medusarum). Photographic evidence of some of these interactions is included in this contribution. This is the first survey of these relationships in the Gulf of California, and many aspects of the ecology and biology of these symbioses remain to be studied.     

Food partitioning among carnivores within feeding guild structure of fishes inhabiting a mudflat ecosystem of Indian Sundarbans

The present study was aimed to determine dietary composition and feeding guild structure of the fishes inhabiting mudflat habitat of Indian Sundarbans. In addition, partitioning of food resources by the fish species belonging to the carnivorous feeding guild was also performed to understand the survival strategies of fish in a mudflat estuarine habitat. Seventeen prey categories were isolated from the stomachs of 31 studied fish species. Overall, five feeding guilds (viz. plankti-benthivore: 12 species, herbivore: one species, detritivore: three species, omnivore: one species and carnivore: 14 species) were identified on the basis of the prey abundance within their stomachs, considering 64 % Bray–Curtis similarity. Among the carnivorous, maximum trophic richness was obtained for Uroconger lepturus followed by Ophichthus apicalis. Teleost and decapods were the main animal prey items preferred by majority of the carnivorous fishes. However, O. apicalis and Terapon jarbua showed their preference toward maximum number of prey categories among carnivores, which was also ratified by the high values for standardized niche breadth presented by them. The maximum degree of interspecific dietary overlap was found between Uropterygius marmoratus and Pseudapocryptes elongatus as both of them were recognized as cranci-piscivore. The lowest was observed between Hyporhamphus limbatus and Coilia neglecta. As food resources are not limiting in the mudflats of Indian Sundarbans, the general patterns of resource partitioning and niche differentiation in resident ecological communities will improve the understanding of the mechanisms underlying species coexistence and community structure.     

Diet and foraging opportunism of the Guiana dolphin (Sotalia guianensis) in the Abrolhos Bank,Brazil

Diet analysis allows exploring how coastal dolphins interact with the environment and their role in the marine food webs. We studied the diet and feeding ecology of the Guiana dolphin, Sotalia guianensis, through analysis of stomach content from 42 animals stranded on the eastern coast of Brazil. A total of 1,336 semidigested prey items (fish, otoliths, cephalopod beaks, and crustaceans) were identified. Teleost fish comprised the most frequent food item (92% of the total), followed by cephalopods, and crustaceans. Prey belonged to 34 taxa and richness in individual stomachs varied from 1 to 15 prey taxa. Prey were generally small, but showed a significant trend to increase in size with dolphin length. The main prey of Guiana dolphins were demersal, estuarine, and sound-making fish such as catfish and sciaenids. No sex-related differences in diet were found. Diet composition varied seasonally and occurrence of prey items was coherent with breeding or high abundance periods of some fish species and squids. Our study shows the importance of demersal prey from estuarine and soft-sediment habitats to Guiana dolphin in the Abrolhos Bank and reveals that feeding habits are generalist and opportunistic, with diet reflecting the seasonal abundance and availability of prey.     

The food and feeding relationships of black oreo, Allocyttus niger, smooth oreo, Pseudocyttus maculatus, and eight other fish species from the continental slope of the south-west Chatham Rise, New Zealand

The food and feeding habits of black oreo and smooth oreo sampled at depths of 600–1200 m from the south-west Chatham Rise in 1983 are described, with notes on prey of eight other fish species. All these fish species fed benthopelagically. Black oreo preyed on hyperiid amphipods, salps and natant decapod crustaceans; smooth oreo on salps and amphipods. Dietary composition of both species changed with size of fish. Aspects of feeding relationships between the fish species were examined including dietary similarity and prey-size selection. Findings are compared with results of research on other New Zealand deepwater fish species.     

Resource seasonality and fish diets in an Illinois stream

Synopsis The purpose of this study was to evaluate the intensity of competition for food among 9 species of stream fishes that primarily eat aquatic invertebrates. The taxonomic and size composition, and numerical abundance of aquatic invertebrates were monitored for one year using drift and benthic samples. Diet data were obtained from stomachs of fishes captured at the same time and place that invertebrate sampling was done. Diet characteristics examined included taxonomic and size composition, number of prey per fish, and diet breadth. Drifting invertebrates were more abundant early in the year (March–June) than later (July–January). The summer-early fall scarcity of invertebrates was especially notable among those>3.6 mm long, which comprised the bulk of prey found in fish stomachs. Average prey size eaten by a fish species was positively correlated with fish mouth size, but interspecific overlap in prey size was extensive. Cyprinids as a group (5 species) ate proportionally fewer small (< 3.6 mm long) prey from July to January than did the centrarchids and stonecat. Taxonomic compositions of available invertebrates and fish diets varied markedly among sampling dates, but the use of prey taxa by fishes was not correlated with the availability of those taxa. Use of aquatic prey taxa was generally similar among fish species, but cyprinids as a group ate proportionally more terrestrial prey from July to January than did the centrarchids and stonecat. Diet breadths for all species increased as food levels declined, indicating that these fishes experienced resource depression. Food scarcity was evidently more severe for cyprinids since their stomachs contained few prey through the summer and fall relative to the centrarchids and stonecat. Though the fish species studied probably compete for food in the summer and fall, this competition did not account for the community structure observed.     

Piscivore diet response to a collapse in pelagic prey populations

Pelagic fish populations in the upper San Francisco Estuary have experienced significant declines since the turn of the century; a pattern known as the pelagic organism decline (POD). This study investigated food habits of piscivorous fishes over two consecutive fall seasons following the decline of pelagic fish prey. Specifically, this study addressed the contribution of pelagic versus benthic prey to piscivorous fish diets, including the frequency of predation on special-status pelagic species, and the spatial variability in prey consumption. The piscivore community was dominated by Striped Bass and also included small numbers of Sacramento Pikeminnow and Largemouth Bass. Overall, pelagic prey items contributed less than 10% of the diet by weight in both years, whereas pre-POD studies gleaned from the literature found contributions of 39–100%, suggesting a major switch from pelagic to benthic prey resources. Between-year variation in piscivore diets reflected differences in environmental conditions associated with variation in freshwater outflow. No special status fish species were detected in any of the piscivore stomachs examined. The consequences of this pelagic to benthic diet shift warrants further investigation to understand its ecological relevance.     

Trophic relationships and seasonal utilization of salt-marsh creeks by zooplanktivorous fishes

Synopsis In a high salinity estuary at North Inlet, South Carolina, co-occurrence and possible competition among adults of four dominant zooplanktivorous fishes were minimized by seasonal adjustments in lateral and vertical distributions as well as in dietary preferences. In winter, Atlantic silversides, Menidia menidia, occupied the entire water column while other planktivores were rare or absent from the estuary, and they consumed large prey such as mysid shrimps and fish larvae. An immigration of bay anchovies, Anchoa mitchilli, in the spring resulted in a redistribution of species with Atlantic silversides shifting to the surface waters and bay anchovies dominating the lower half of the water column. Both fishes consumed mostly copepods in the spring, but each favored a different species. There was little similarity in the large prey items consumed by the two fishes. Striped anchovies, Anchoa hepsetus, arrived in mid-summer and were most abundant at the surface while bay anchovies continued to dominate the bottom waters. Atlantic silversides were rare in all summer collections. The diets of the two anchovies were similar, but vertical separation during the period of maximum zooplankton abundance probably minimized competition. Rough silversides, Membras martinica, which were obligate surface dwellers, shared the upper water column with striped anchovies, but the two species had very different diets during their period of co-occurrence. Although seasonal changes in fish diets reflected shifts in zooplankton composition and all fishes consumed a variety of prey types, preferences for some prey taxa and total avoidance of others were indicated. Electivity indices indicated an especially strong selection for fiddler crab megalopae by all fishes in the summer and fall. All fishes, except rough silversides, which fed almost exclusively on copepods and crab zoeae, consumed large prey items when they were available. Fine scale partitioning of the food resources was apparent in the selection of different copepod and insect species by the fishes. Spatial and temporal separation in the distribution and/or dietary preferences of the zooplanktivores fishes probably reduces the potential for resource competition. Given the high abundances and selectivity of the planktivores, significant impacts on some zooplankton populations probably result.     

Diet seasonality and food overlap among fishes of the upper Orituco stream, northern Venezuela.

The diets of four diurnal fish species (Creagrutus bolivari, Knodus deuterodonoides, Knodus sp. and Poecilia reticulata) were examined during a year in the Orituco stream at northern Venezuela. The fishes were sampled monthly from February 1991 to March 1992 (except October 1991 and February 1992) in the stream main channel with a beach seine and a cast net. Diet is reported as frequency of occurrence and numeric proportion because variation in prey sizes was small. Non-parametric statistical tests were applied. A total of 18 distinct prey items were found in stomachs. The diet of these fishes consisted of aquatic insects (Coleoptera, Diptera, Hemiptera, Odonata, Plecoptera and Trichoptera), allochthonous plant matter (fragments of leaves and seeds), microalgae (Chlorophyta and Bacillariophyceae) and terrestrial arthropods (Coleoptera, Diptera, Hymenoptera and Arachnida). The low percentage of empty guts and the high fullness percentage of guts suggest that food was always abundant. Aquatic insects were more important in the dry season (November-April) while plant matter and terrestrial arthropods increased in the wet season (May-October). The Proportional Similarity Measure (PS) was high between characid species and low between characids and P. reticulata in the dry season. PS decreased during the wet season because of a reduction in aquatic insect consumption. The seasonal diet shift indicated the greater importance of allochthonous food only in the wet season.     

Diet assessment of the Atlantic Sea Nettle Chrysaora quinquecirrha in Barnegat Bay,New Jersey,using next‐generation sequencing

Next‐generation sequencing (NGS) methodologies have proven useful in deciphering the food items of generalist predators, but have yet to be applied to gelatinous animal gut and tentacle content. NGS can potentially supplement traditional methods of visual identification. Chrysaora quinquecirrha (Atlantic sea nettle) has progressively become more abundant in Mid‐Atlantic United States’ estuaries including Barnegat Bay (New Jersey), potentially having detrimental effects on both marine organisms and human enterprises. Full characterization of this predator's diet is essential for a comprehensive understanding of its impact on the food web and its management. Here, we tested the efficacy of NGS for prey item determination in the Atlantic sea nettle. We implemented a NGS ‘shotgun’ approach to randomly sequence DNA fragments isolated from gut lavages and gastric pouch/tentacle picks of eight and 84 sea nettles, respectively. These results were verified by visual identification and co‐occurring plankton tows. Over 550 000 contigs were assembled from ~110 million paired‐end reads. Of these, 100 contigs were confidently assigned to 23 different taxa, including soft‐bodied organisms previously undocumented as prey species, including copepods, fish, ctenophores, anemones, amphipods, barnacles, shrimp, polychaete worms, flukes, flatworms, echinoderms, gastropods, bivalves and hemichordates. Our results not only indicate that a ‘shotgun’ NGS approach can supplement visual identification methods, but targeted enrichment of a specific amplicon/gene is not a prerequisite for identifying Atlantic sea nettle prey items.     

Warming Ocean Conditions Relate to Increased Trophic Requirements of Threatened and Endangered Salmon

The trophic habits, size and condition of yearling Chinook salmon (Oncorhynchus tshawytscha) caught early in their marine residence were examined during 19 survey years (1981–1985; 1998–2011). Juvenile salmon consumed distinct highly piscivorous diets in cold and warm ocean regimes with major differences between ocean regimes driven by changes in consumption of juvenile rockfishes, followed by several other fish prey, adult euphausiids and decapod larvae. Notable, Chinook salmon consumed 30% more food in the warm versus cold ocean regime in both May and June. Additionally, there were about 30% fewer empty stomachs in the warm ocean regime in May, and 10% fewer in warm June periods. The total prey energy density consumed during the warmer ocean regime was also significantly higher than in cold. Chinook salmon had lower condition factor and were smaller in fork length during the warm ocean regime, and were longer and heavier for their size during the cold ocean regime. The significant increase in foraging during the warm ocean regime occurred concurrently with lower available prey biomass. Adult return rates of juvenile Chinook salmon that entered the ocean during a warm ocean regime were lower. Notably, our long term data set contradicts the long held assertion that juvenile salmon eat less in a warm ocean regime when low growth and survival is observed, and when available prey are reduced. Comparing diet changes between decades under variable ocean conditions may assist us in understanding the effects of projected warming ocean regimes on juvenile Chinook salmon and their survival in the ocean environment. Bioenergetically, the salmon appear to require more food resources during warm ocean regimes.     

Feeding patterns of the dominant benthic and demersal fish community in a temperate estuary

The diet and feeding relationships of the 12 most abundant benthic and demersal fish species of the Mondego Estuary, Portugal, were studied between June 2003 and May 2006. Fishes were caught during the night using a 2 m beam trawl. The stomach contents were analysed for prey identification, counting and weighing. According to prey importance in diets, three main feeding guilds were identified: (1) invertebrate feeders, (2) invertebrate and fish feeders and (3) plankton and invertebrate feeders. Besides these main feeding guilds, some fishes also presented fractions of algae and zooplankton in their stomach contents. The most abundant prey items were macroinvertebrates, with several polychaetes ( Nephtys spp., Capitellidae, Spionidae and Eunicidae), Corophium spp. and Crangon crangon among the dominant prey. Pomatoschistus spp. were the most preyed on fishes. Several fish species showed a tendency for a specialized diet, but almost all also showed some degree of opportunistic feeding by preying on other food resources. High diet overlap was found between some fish species, yet exploitative competition could not be concluded.     

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.     

Interactions of pelagic cnidarians and ctenophores with fish: a review

Medusae, siphonophores and ctenophores (here grouped as `pelagic coelenterates') interact with fish in several ways. Some interactions are detrimental to fish populations, such as predation by gelatinous species on pelagic eggs and larvae of fish, the potential competition for prey among pelagic coelenterates and fish larvae and zooplanktivorous fish species, and pelagic coelenterates serving as intermediate hosts for fish parasites. Other interactions are positive for fish, such as predation by fish on gelatinous species and commensal associations among fish and pelagic coelenterates. The interactions range from beneficial for the gelatinous species (food, parasite removal), to negative (predation on them). We review existing information and present new data on these topics. Although such interactions have been documented frequently, the significance to either fish or pelagic coelenterate populations is poorly understood. The effects of pelagic coelenterates on fish populations are of particular interest because of the great importance of fisheries to the global economy. As fishing pressures mount, it becomes increasingly important to understand how they may influence the balance between pelagic coelenterates and fish.     

Coping with the cold: energy storage strategies for surviving winter in freshwater fish

For many ectothermic animals, the acquisition, storage and depletion of lipids is integral to successfully coping with reduced metabolic rates and activity levels associated with cold, winter periods. In fish, lipids are crucial for overwinter survival and successful reproduction. The timing and magnitude of seasonal lipid storage should therefore vary predictably among fish with different thermal preferences and spawn times. Small‐ and large‐bodied fish should also face different constraints associated with season that influence lipid cycling. However, much work to date has been species‐ and location‐specific and a general conceptual model for the seasonal energy budgets of freshwater fish is lacking. Here, we conducted a comprehensive literature review of seasonal lipid levels in freshwater fishes. We predicted that warm and cool water species would be more likely to demonstrate peak lipid levels during warm months than cold water species, and expected a larger magnitude of annual lipid cycling in warm and cool water compared to cold water fish. We also expected dampened lipid cycling in larger fish due to their lower mass‐specific metabolic rates. Observed patterns in the timing and magnitude of lipid storage contradicted our prediction because lipid cycling was widespread across species, despite thermal guild, with peak lipid levels commonly occurring during warmer months, even in cold water fish. For body size effects, larger bodied fish species had dampened seasonal lipid cycling, as predicted. We developed a conceptual framework describing how the ‘scope’ for variation in annual lipid cycling changes with body size both among and within species in order to guide future work. Together, our findings suggest that energy acquired during warm months is broadly important for overwinter survival and reproduction in fishes, and provide a new perspective on the differential constraints and physiological responses to seasonality among freshwater fish. Improving our understanding of these dynamics is especially pressing given that a changing global climate is anticipated to alter existing seasonal signals.     

Comparative experimental studies on the feeding of chaetognaths and ctenophores

There is very little quantitative experimental information onfeeding in chaetognaths and ctenophores because of the difficultyof obtaining undamaged specimens. As important plankton predators,a knowledge of their daily rations as a function of food concentrationis vital to ecosystem models of water column trophodynamics.At specified food concentrations, three ctenophore species alwaysingested higher specific daily rations than three species ofchaetognaths. Food consumption of ctenophores increased linearlythroughout the food concentration range (exceeding 10⁶ µgC/m³ Although food consumption of chaetognaths reached an upperlimit at very high food concentrations, it seemed unlikely thatsatiation would occur under environmental conditions. Below10,000 food items/m³ chaetognaths were unable to obtain l% oftheir specific daily ration, although the few environmentalstudies based on gut contents suggest substantial feeding evenbelow this concentration. The apparent threshold may reflectthe environmental patch density necessary for feeding to begin.At high food concentrations daily rations of newly-hatched ctenophoresand chaetognaths can exceed well over 10 times their body carbon.In ctenophores even adults can consume these extremely largerations although chaetognaths follow the more usual pattern,where ration decreases throughout life. Gut residence time offood (where single items were ingested) increased with age andsize of food item selected in Sagitta hispida from one to twohours, levelling off after animals reached 6 mm. Mnemiopsismccradyi maintained a uniform digestion time of one hour asit grew, except for a brief period when it first selected larger-sizedfood. In older animals of both species, multiple ingestion becamemore common, where gut residence time was directly proportionalto number of food items consumed, ranging up to 5 hours forfive or more food items. Chaetognaths showed more variabilityof gut residence time than did ctenophores. It was concludedthat these animals are much better at catching food in the environmentthan laboratory experiments would suggest.     

Diet and feeding habits of Economidichthys pygmaeus (Perciformes: Gobiidae) in Lake Pamvotis,NW Greece

The purpose of the study was to define the diet composition, feeding preferences, seasonal, size and sex related changes in diet, feeding strategy and diel cycle of Economidichthys pygmaeus. Important features of the overall feeding patterns of the goby include (i) feeding activity, (ii) bottom habits and (iii) consumption of food items to identify the dietary breadth. Stomach contents of 533 specimens, 13.42–48.65 mm total length (TL), collected by hand net (2 mm mesh size) from October 2006 to September 2007 were analyzed. The percentage of 76 empty stomachs (14.26%) did not vary significantly with season. The food composition suggested that the goby is a carnivorous fish. Prey items identified in the stomachs belonged to four major groups: Crustaceans, Insects, Mollusca and Plants. Copepods were the most important (%IRI = 57.51), especially in fish larger than 23 mm TL. Chironomids (%IRI = 43.23) constituted the main prey for fish <23 mm TL. Diet composition showed little seasonal variation. Copepoda dominated the diet in autumn and winter (43.4%; 82.4%) and were replaced by Chironomidae larvae in spring (39.7%) and summer (47.7%). During the reproductive season, large males show a narrow food spectrum as opposed to large females, reflecting the different activity pattern exhibited by males and females during the breeding season, since the former supports parental care. According to the modified Costello graphical method, specialist individuals form the goby population that feeds on two preferential prey types (e.g. Copepods, Chironomids). Nevertheless, they consume some occasional prey (e.g. Cladocera, Insects, Gastropods). The species foraged chiefly at night and early morning, during lower light intensity. The highest feeding activity recorded at night (02.00 hours) and during early morning (08.00 hours) could be related to the cryptic behaviour displayed by the species.