Feeding habits of ocellate spot skate,Okamejei kenojei (Müller & Henle, 1841), in coastal waters of Taean,Korea

The feeding habits of Okamejei kenojei were studied using 592 specimens collected in the coastal waters of Taean, Korea from April 2008 to March 2009. O. kenojei is a bottom‐feeding carnivore that consumes mainly shrimp, fishes, and crabs. Its diet also includes small quantities of amphipods, mysids, cephalopods, euphausiids, copepods, isopods, and polychaetes. The total length (TL) of individuals in this study ranged from 8.2 to 49.0 cm. Cluster analysis based on %IRI (index of relative importance) identified three size classes. Group A (< 20 cm TL) ate primarily caridean shrimp and amphipods; group B (20–30 cm TL) ate exclusively shrimp; and group C (> 30 cm TL) ate penaeoidean shrimp, fishes, and crabs. O. kenojei showed ontogenetic changes in feeding habits. Although shrimps were the primary food consumed by all size groups, the proportion of shrimp in the total diet decreased and the consumption of fishes and crabs gradually increased with the body size of O. kenojei. Size of the prey organisms also increased. Smaller individuals fed mainly on small prey, such as amphipods, mysids, and small shrimp, whereas larger individuals preferred larger prey, such as larger shrimp, fishes, and crabs. The size‐related diet breadth and the percentage of empty stomachs were significant; the diet breadth gradually increased with body size, whereas the percentage of empty stomachs decreased. Seasonal changes in the O. kenojei diet were not significant, but shrimp constituted 97.3% of the summer diet by %IRI. Seasonal changes in diet breadth and the percentage of empty stomachs were not significant.     

A smaller particle size improved the oral bioavailability of monkey head mushroom, Hericium erinaceum, powder resulting in enhancement of the immune response and disease resistance of white shrimp, Litopenaeus vannamei

The effects of different particle sizes (100–150, 74–100, and <74 μm) of powder of the dried and ground stipe from the monkey head mushroom, Hericium erinaceum, on the immune response and disease resistance of white shrimp, Litopenaeus vannamei, against the pathogen, Vibrio alginolyticus, were examined. Mushroom powder with a particle size of <74 μm had a significantly higher effect on the disease resistance of shrimp compared to particle sizes of >74 μm. Mortality of shrimp after being injected with V. alginolyticus was particle size-dependent, increasing from 66.7% ± 3.3%–93.3% ± 3.3% with diets containing stipe particle sizes of <74 and 100–150 μm, respectively. The mortality of shrimp fed the diet containing <74-μm stipe powder for 28 days was significant lower than that of shrimp fed with the control diet and the diet containing 74–100-μm stipe powder after being challenged by V. alginolyticus. The optimal concentration of the <74-μm mushroom powder for enhancing the immune response and disease resistance of shrimp was 0.2 μg (g shrimp)^?1 day^?1. No significant change in the total hemocyte count, differential hemocyte count, glutathione reductase, or phagocytic activity was found in shrimp fed the control diet and mushroom powder-containing diet at a level of up to 0.2 μg (g shrimp)^?1 day^?1. Shrimp fed 0.2 μg (g shrimp)^?1 day^?1 of a mushroom-containing diet had a significantly higher disease resistance to V. alginolyticus via an increase in phenoloxidase activity, respiratory bursts, superoxide dismutase activity, and glutathione peroxidase activity. Therefore, a diet containing the stipe powder of monkey head mushroom with a particle size <74 μm at a level of 0.2 μg (g shrimp)^?1 day^?1 was found to enhance the immunity and disease resistance of shrimp.     

Reproductive biology of Chinese minnow Hemiculterella sauvagei Warpachowski, 1888 in the Chishui River,China

This study describes the reproductive biology of the Chinese minnow Hemiculterella sauvagei. The length‐weight relationship, sex ratio, spawning season, size at first maturity, and fecundity were analyzed based on 685 specimens collected from the Chishui River between July 2011 and July 2012. The relationship between standard length (SL) and body weight (BW) were estimated as BW = 2.14 × 10^?4 × SL^2.801 (R² = 0.839; N = 413; P < 0.05) for females and BW = 1.31 × 10^?4 × SL^3.001 (R² = 0.868; N = 272; P < 0.05) for males. The female to male sex ratio, 1.52 : 1, differed significantly from a 1 : 1 ratio. Females predominated in standard lengths >12 cm. Analyses of the monthly variation in the gonadosomatic index (GSI), the monthly proportions of macroscopic gonadal maturity, and the size distribution of oocytes consistently suggested a prolonged spawning season of H. sauvagei from March to August, with a peak from April to May. Logistic curves describing the relationship between proportion of maturity (P_r) at each length interval and standard length were estimated as P_r = 1/(1 + e^{26.867–0.306SL}) (R² = 0.999; N = 413; P < 0.05) for females and P_r = 1/(1 + e^{10.522–0.142SL}) (R² = 0.999; N = 272; P < 0.05) for males. Size at first maturity was estimated as 7.4 cm for males and 8.8 cm SL for females. Absolute fecundity varied from 563 to 5052, with a mean of 2413 ± 874 oocytes per ovary. The relative fecundity was estimated to be 41–299, with a mean of 171 ± 55 oocytes per ovary. The present study provides useful information for fishery management and resources conservation.     

Feeding dynamics,consumption rates and daily ration of wahoo Acanthocybium solandri in Indo‐Pacific waters

This study reports the diet composition of 363 wahoo Acanthocybium solandri captured from the Indo‐Pacific. The study also provides the first estimates of consumption and daily ration for the species worldwide, which are important parameters for ecosystem models and may improve ecosystem‐based fisheries management. Thirty‐four prey taxa were identified from A. solandri stomachs with Scombridae having the highest relative importance. Actinopterygii comprised 96% of the total prey wet mass, of which 29% were epipelagic fishes, with 22% alone from Scombridae. There was no significant relationship between fish size and the size of prey items consumed. Feeding intensity, as measured by stomach fullness, did not significantly differ either among seasons or reproductive activity. The mean daily consumption rate was estimated as 344 g day^?1, which corresponded to a mean daily ration of 2·44% body mass day^?1. The results from this study suggest A. solandri is an opportunistic predator similar to other pelagic piscivores, worldwide.     

Age and growth characteristics of Schizopygopsis younghusbandi Regan, 1905 in the Yarlung Tsangpo River in Tibet,China

To better understand the biology of Schizopygopsis younghusbandi Regan, 1905 and its relationship with management considerations, this study describes the relationships between otolith size and fish length and age, verifies annual periodicity of otolith annulus formation, and estimates the S. younghusbandi growth parameters. These age and growth characteristics were studied using 694 specimens collected from August 2008 to August 2009. Otoliths grew asymmetrically throughout the range of standard length (SL) studied, showing a clear pattern of alternating translucent and opaque bands. Marginal increment ration (MIR) analysis of specimens up to 6 years of age indicated that one opaque band and one translucent band were laid down each year. Maximum observed age was 17 years, corresponding to a female of 35.8 cm SL and 589.1 g body weight (BW). The SL‐BW relationship was described as BW = 1.122 × 10^?5 SL^3.030 for sexes combined. The von Bertalanffy growth function was used to model back‐calculated lengths as L_t = 338.4 (1?e^{?0.233 (t + 0.403)}) for males, and L_t = 433.9 (1?e^{?0.194 (t + 0.397)}) for females. Growth performance of S. younghusbandi was relatively higher than those of other Schizothoracinaes inhabiting the same river.     

Sap flow variation in selected riparian woodland species in the Okavango Delta,Botswana

In the tropical Okavango Delta, transpiration by trees is an important process partly responsible for maintaining the basin as a freshwater environment. Quantification of evapotranspiration from terrestrial landforms of the delta, fringed by riparian woodlands, is one of the main contributors to uncertainty in current hydrological modelling. We investigated sap flow of common trees in the distal, mid‐ and upper delta in July–August 2012, November–December 2012 and February–April 2013 using the compensation heat pulse velocity method. In the distal delta, four Diospyros mespiliformis individuals of different sizes were studied. Four trees of different species were studied in the mid‐ and upper delta. Sap flow density (SFD; flow per unit cross‐sectional area) was used as a common unit to facilitate comparison. Sap flow varied with tree size, species, season and location. It was positively correlated with tree size (r² = 0.67). Sap flow variation between seasons and across locations in all the species studied indicated two distinct groups. Group 1 transpired the least during the hottest season, November–December, and Group 2 the most. In Group 1, the highest average SFD was 1.17 l cm^?2 day^?1 during July–August; in Group 2, it was 1.07 l cm^?2 day^?1 during November–December. Changes in the hydrology of the delta would negatively affect the riparian woodland.     

Contribution to the feeding ecology of the predatory wingfin anchovy Pterengraulis atherinoides (L.) in north Brazilian mangrove creeks

Stomach contents were examined from 136 Amazonian wingfin anchovy, Pterengraulis atherinoides (Engraulidae), caught from intertidal mangrove creeks at diurnal neap tides between June and September 1997 (early dry season) near Bragança (northern Brazil). The study found that P. atherinoides are specialized predators of juvenile Natantia and Teleostei (mean: 67 and 28% by dry weight, respectively). On average, 5.2 g ha^?1 day^?1 of Natantia and 2.6 g ha^?1 day^?1 of Teleostei (wet weight) were eaten by P. atherinoides. Diet changed with fish size as well as by month. While smaller sizes still fed on several food items (e.g. the copepod Pseudiaptomus marshii, the brachyuran crab Pachygrapsus gracilis, amphipods), fish >13 cm standard length (SL) fed exclusively on Natantia and Teleostei. Copepods were especially abundant in July and August, dominating the diet of fish <9 cm SL in numbers (92%). Our results suggest a positive relationship between predator size and prey size, both in penaeid and piscine prey. However, the largest predator size class apparently selected fewer but larger Teleostei prey. More than 64% of Natantia were juvenile penaeid shrimps of commercial importance (Fenneropenaeus subtilis, F. schmitti, Xiphopenaeus kroyeri). Comparison with ichthyoplankton samples taken simultaneously showed that Sciaenidae and Mugilidae were positively selected while Gobiidae and Engraulidae were negatively selected. The presence of pranzia larvae in the stomachs of fish <10 cm SL, from July onward, suggests that these sizes fulfil a mutually beneficial ‘cleaning’ function on other fish. Block net sampling at neap tides showed that P. atherinoides were present in intertidal mangrove creeks throughout the submergence period, suggesting temporal optimization of the foraging time in the eulittoral.     

Prey selection and diel feeding of the freshwater jellyfish, Craspedacusta sowerbyi

1. The diet of the invasive freshwater jellyfish, Craspedacusta sowerbyi (Lankester), was assessed by analysing its stomach contents. 2. The medusae ingested various zooplankton and benthic prey in the 0.1–3.0 mm size range. The selectivity indices for prey showed that larger zooplankton (0.4–1.4 mm) and active prey such as copepods were preferred; small potential prey, and the loricate rotifer Keratella cochlearis in particular, were almost never consumed. Measurements suggest that spacing between the tentacle branches could determine prey selection. Another possibility is that some prey are too small or slow to activate nematocysts after collision with the predator. Prey > 1.4 mm can probably escape or are otherwise too large to be handled. 3. The medusae of Craspedacusta medusae stayed in deep water during daytime and migrated upwards at night. The greatest number of prey in freshwater jellyfish stomachs was detected at night. 4. Calculation of consumption rates, based on mean stomach contents and digestion times of 4–5 h, showed that, on average, one medusa takes 190 zooplankton prey day^??1 at a mean prey density of about 100 L^??1. At the observed medusae density of 1 m^??3, the cropping rate was about 0.2 zooplankton prey L^??1 day^??1.     

Polygonal tundra geomorphological change in response to warming alters future CO2 and CH4 flux on the Barrow Peninsula

The landscape of the Barrow Peninsula in northern Alaska is thought to have formed over centuries to millennia, and is now dominated by ice‐wedge polygonal tundra that spans drained thaw‐lake basins and interstitial tundra. In nearby tundra regions, studies have identified a rapid increase in thermokarst formation (i.e., pits) over recent decades in response to climate warming, facilitating changes in polygonal tundra geomorphology. We assessed the future impact of 100 years of tundra geomorphic change on peak growing season carbon exchange in response to: (i) landscape succession associated with the thaw‐lake cycle; and (ii) low, moderate, and extreme scenarios of thermokarst pit formation (10%, 30%, and 50%) reported for Alaskan arctic tundra sites. We developed a 30 × 30 m resolution tundra geomorphology map (overall accuracy:75%; Kappa:0.69) for our ~1800 km² study area composed of ten classes; drained slope, high center polygon, flat‐center polygon, low center polygon, coalescent low center polygon, polygon trough, meadow, ponds, rivers, and lakes, to determine their spatial distribution across the Barrow Peninsula. Land‐atmosphere CO₂ and CH₄ flux data were collected for the summers of 2006–2010 at eighty‐two sites near Barrow, across the mapped classes. The developed geomorphic map was used for the regional assessment of carbon flux. Results indicate (i) at present during peak growing season on the Barrow Peninsula, CO₂ uptake occurs at ‐902.3 10⁶gC‐CO₂ day^?1 (uncertainty using 95% CI is between ?438.3 and ?1366 10⁶gC‐CO₂ day^?1) and CH₄ flux at 28.9 10⁶gC‐CH₄ day^?1(uncertainty using 95% CI is between 12.9 and 44.9 10⁶gC‐CH₄ day^?1), (ii) one century of future landscape change associated with the thaw‐lake cycle only slightly alter CO₂ and CH₄ exchange, while (iii) moderate increases in thermokarst pits would strengthen both CO₂ uptake (?166.9 10⁶gC‐CO₂ day^?1) and CH₄ flux (2.8 10⁶gC‐CH₄ day^?1) with geomorphic change from low to high center polygons, cumulatively resulting in an estimated negative feedback to warming during peak growing season.     

Seasonal variation in the diet of juvenile lake sturgeon,Acipenser fulvescens,Rafinesque, 1817, in the Winnipeg River,Manitoba, Canada

The lake sturgeon, Acipenser fulvescens, is a threatened species across most of its range. To understand any potential shifts in diet across season or habitat, stomach contents were examined from juvenile lake sturgeon caught in the Winnipeg River, Manitoba, Canada. This information will aid in assessment of environmental impacts and conservation initiatives for this threatened species. From 2006 to 2008 gut contents were collected from juvenile lake sturgeon using a non‐lethal gastric lavage methodology. Juvenile lake sturgeon were sampled from four discrete deep water habitat types (13.7–27.4 m depths), during the months of May, June, July and October. In total, 13 066 prey items belonging to 14 prey groups were collected from 345 juvenile lake sturgeon (251–835 mm TL). Overall, juvenile lake sturgeon consumed a low diversity of organisms; insect larvae from three invertebrate orders, Trichoptera, Diptera and Ephemeroptera, accounted for 97.4% of the total numeric abundance of prey items recovered. A relationship between size of juvenile lake sturgeon and prey quantity or type was not observed. Diet of juvenile lake sturgeon varied in relation to season, with Diptera (77.6%) being the most abundant prey in May, Trichoptera the most abundant in June (n = 3,056, 60.4%) and July (n = 2,055, 52.6%). During October, 96% of stomachs examined were empty. In terms of habitat type, the standardized abundance of invertebrate prey items was highest in deep water habitats characterized by medium water velocity (depths > 13.7 m) and coarse substrate (particle sizes > 0.063 mm) in May and June when compared to deep water habitats characterized by low water velocity (<0.2 m.s^?1) and fine substrate (particle sizes < 0.063 mm). However, in July, the opposite was observed and prey abundance in juvenile lake sturgeon stomachs decreased with increasing particle size. Results suggest a high degree of dietary overlap among juvenile lake sturgeon from multiple size/age classes occupying deep‐water habitats of the Winnipeg River.     

Age,growth and maturity of tub gurnard (Chelidonichthys lucerna Linnaeus 1758; Triglidae) in the inshore coastal waters of Northwest Wales,UK

The tub gurnard Chelidonichthys lucerna has been identified by ICES as a potential commercial species in the northeast Atlantic with recommendations made to monitor landings and discards and to derive information on population biology for stock assessment purposes, however, data are lacking for the species in the northeast Atlantic. Therefore, aims of this study were to provide data on the size/age‐structure and patterns of growth, maturity and mortality of C. lucerna in Northwest Wales, UK, and in doing so to provide data on the biological characteristics of the most northerly population studied to date for comparison with the existing data for southerly Mediterranean populations. Data on the age, growth and maturity of C. lucerna were collected by otter trawling (73 mm cod‐end stretched mesh size) in the coastal waters of Northwest Wales, UK in October (2000–2011, excluding 2006). Total length (TL) of fish sampled ranged between 10.5–41.0 cm (males) and 10.4–57.5 cm (females). The majority of the female fish were between 20–30 cm TL (60.2%) and the majority of the male fish between 20–30 cm TL (58.3%) respectively. TL/weight (W) relations for male and female fish were similar and the combined data was described by W = 0.0067 TL^3.10. Age of fish ranged between 1–7 years old for female fish and 1–5 years old for male fish respectively with the majority of female fish 3 years old (40%) and the majority of male fish 3 years old (37%). The age structures of female and male tub gurnards were not significantly different with the older age classes consisting predominantly of female fish. Both males and females exhibited similar asymptotic growth patterns and the combined von Bertalanffy growth function was TL_t = 51.6 (1 ? e ^{[?0.25(t + 0.41)]}). Instantaneous rates of total mortality were calculated as 1.04 year^?1 for males and 1.11 year^?1 for females. The size (L₅₀) and age at first maturity (A₅₀) were estimated to be 29.1 cm TL and 2.8 years for males, 27.7 cm TL and 2.7 years for females and 28.0 cm TL and 2.8 years for both sexes combined. The results of this study provide the first information on the biology and population dynamics of C. lucerna in the Irish Sea, the first data collected in the northeast Atlantic since 1985 and the most northerly population studied to date.     

Preliminary results on growth and feeding of wild-caught young goldblotch grouper, Epinephelus costae, in captivity

Growth, food intake, feed conversion, survival, and behaviour of wild‐caught goldblotch grouper, Epinephelus costae Steindachner, (initial weight=103.04 ± 8.27g) were evaluated when reared in captivity. Average weight gains ranged between 0.106 and 0.278 g day^?1, while corresponding gains in length ranged between 0.005 and 0.018 cm day^?1. Average daily growth rate was between 0.075 and 0.232% body weight day^?1 (overall 0.141 ± 0.08% bw/day). Daily rate of feeding was estimated to be between 0.299 and 0.418% bw day^?1 (overall 0.365 ± 0.09% bw day^?1). Food conversion ratio (FCR) ranged between 0.21 and 0.77 (overall FCR=0.423). Food intake was dependent on water temperature.     

Comparative feeding ecology of shortfin mako, blue and thresher sharks in the California Current

This study describes the feeding ecology of three pelagic shark species in the California Current: shortfin mako (Isurus oxyrinchus); blue (Prionace glauca); and thresher (Alopias vulpinus) sharks. Stomach contents of sharks collected from 2002 to 2008 were identified to the lowest taxonomic level and analyzed using univariate and multivariate methods. Of 330 mako sharks sampled (53 to 248?cm fork length [FL]), 238 stomachs contained 42 prey taxa, with jumbo squid (Dosidicus gigas) and Pacific saury (Cololabis saira) representing the most important prey based on the geometric index of importance (GII). In addition, 158 blue sharks were sampled (76 to 248?cm FL) and 114 stomachs contained 38 prey taxa, with jumbo and Gonatus spp. squids representing the most important prey. Lastly, 225 thresher sharks were sampled (108 to 228?cm FL) and 157 stomachs contained 18 prey taxa with northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) identified as the most important prey. Overall, mako sharks had the most diverse diet based upon Simpson??s diversity index (1/D) (8.43?±?1.16), feeding on many species of teleosts and cephalopods, followed by blue sharks (6.20?±?2.11) which consumed a wide range of prey (primarily cephalopods), while thresher sharks were most specialized (2.62?±?0.34), feeding primarily on coastal pelagic teleosts. Dietary overlap was lowest between blue and thresher sharks (S?rensen similarity index?=?0.321 and Simplified Morisita Horn index?=?0.006), and seasonal variability in diet was greatest for blue sharks (Simplified Morisita Horn index?=?0.260, Analysis of Similarity (ANOSIM) p?<?0.001). In addition, size class, and subregion were significant factors that affected diet of each species differently (ANOSIM p?<?0.001). Despite similarities in life history characteristics and spatial and temporal overlap in habitat, diets of these three common shark species are distinct in the California Current.     

Shifts in reciprocal river‐riparian arthropod fluxes along an urban‐rural landscape gradient

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Difference in age,growth, and sexual demography of black‐spot tuskfish,Choerodon schoenleinii (Valenciennes, 1839), in two adjacent populations,Ryukyu Archipelago,southern Japan

To better understand the plasticity of life history traits in the blackspot tuskfish, Choerodon schoenleinii (Valenciennes, 1839), the characteristics of the population around the Yaeyama Islands (24°N, 124E) were examined and compared to those around Okinawajima Island (26°N, 128E) that had been investigated in a previous study. Age and growth of the Yaeyama population were examined based on 103 specimens collected at fish markets between 2006 and 2016. Specimens included 83 females (25.2–69.0 cm total length [TL]), and 20 males (43.1–71.8 cm TL). Ages determined from sectioned otoliths ranged from 1–9 for females, and 4–15 for males. Values for von Bertalanffy growth functions were L_t = 74.2 {1?exp[?0.23 (t + 0.38)]}, and the growth of the Yaeyama population was significantly faster than that of the previously studied population. Sexual demography of the two populations was compared using body length data on landings measured at the fish markets. In the Yaeyama population, females and males ranged from 24–65 cm TL and 39–75 cm TL, respectively; length at 50% individual sex change size was estimated at 54.7 ± 0.56 cm (±95% C.I.). In contrast, in the Okinawajima population, females and males ranged from 16–65 cm TL and 30–75 cm TL, respectively; meanwhile, 50% sex change size was estimated to be 50.0 ± 0.25 cm. There were thus significant differences in the size at sex change between the two populations. This difference may be related to the difference in population density between the sites.     

Population pattern and dynamics of the Bluemouth Helicolenus dactylopterus (Delaroche, 1809) in the eastern Mediterranean Sea

Present study evaluated the population status of the Bluemouth (Helicolenus dactylopterus) population distributed in the Antalya Bay for the first time, within the scope of two different surveys carried out in monthly basis, between September 2009 and June 2011 (200–900 m). In accordance with the major availability of the food, 80.9% of the total catch (in number) of the species at the upper slope (200–499 m). The 80.8% of all recruits’ specimens inhabits between 200 and 399 m while 72% of the total spawner specimens (TL ≥ 20 cm) inhabits at depths of between 600 and 799 m. Highest average abundance of the species was estimated 1,060 n/km² (400 m), while the highest average biomass was 93 kg/km² (600 m). Lengths of individuals ranged from 4 to 36 cm, and estimated ages from 0 to 27 years. Parameters of the von Bertalanffy growth curves were L _∞   = 34.14 cm, K = 0.09 year^?1, and t₀ = ?1.28 years. Margin band analysis confirmed the formation of a single growth annulus per year. In the central part of the otolith, close to the nucleus, a strongly marked check ring is formed which presenting first time for this species in the literature. The duration of the spawning stage for the females was observed between December and February. Selectivity rate of the commercially used 44 mm diamond codend mesh, with a 7.4 cm catch size, found to be very low for the species (a first spawning size of 17–20 cm). The stock of Bluemouth in the Antalya Bay was considered in above reference levels and in high abundance status due to estimated low fishing mortality (0.067^?1), exploitation rate status below reference level (0.207^?1) and F_curr is very low than reference point (0.219^?1).     

Fluctuating water levels control water chemistry and metabolism of a charophyte‐dominated pond

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Diet composition of greater weever,Trachinus draco (Linnaeus, 1758) captured in the eastern‐central Adriatic Sea in relation to fish size,season and sampling area

The diet compositions of greater weever, Trachinus draco, from the eastern‐central Adriatic Sea, were investigated with respect to seasons, fish size and sampling locations. Analyzed were the stomach contents of 592 specimens, total length (TL) of 9.9–31.2 cm, collected by commercial bottom trawls from January to December 2008. The frequency of empty stomachs varied significantly with the season (43.3% maximum during winter; 6.8% minimum during summer). Prey items identified in the stomachs belonged to seven major taxonomic groups: Bivalvia, Cephalopoda, Decapoda, Mysidacea, Isopoda, Amphipoda and Teleostei. Decapods were the most important prey (%IRI = 72.8) followed by teleosts (%IRI = 16.4) and mysids (%IRI = 15.0); other prey groups were only occasionally ingested. Diet composition showed little seasonal variation; decapods were the most important prey in all seasons. Fish size was the most important factor influencing the composition of the diet. Small individuals (<15 cm TL) fed primarily on small crustaceans (mysids), whereas larger fish consumed bigger prey, such as decapods, teleosts and cephalopods. There was high dietary similarity between sampling locations. Based on the diet, greater weever can be a considered a generalistic predator.     

Growth rate of tank-reared Mediterranean amberjack, Seriola dumerili (Risso 1810) fed on three different diets

Mediterranean amberjack Seriola dumerili (Risso 1810) has aquaculture potential. The growth rate and food conversion ratio of S. dumerili on three different types of food (A: 100% frozen sardines; B: 50% frozen sardines and 50% pellet; C: 100% pellet) were measured, and analysed with respect to temperature, condition index and chemical composition of the fish fillet. Wild S. dumerili, average body weight 248 g and average total length 26.9 cm were caught in August and September 1994 in the South Adriatic Sea near Dubrovnik, Croatia and kept in three tanks (n=15 in each tank; duration of experiment, 226 days). The fish that were fed on diet A [initial weight, 252 ± 71 g; total length (TL), 24.3 ± 2.6 cm] started feeding immediately; however, fish assigned to diet C began to feed entirely on the pelleted diet 1 month after the start of the experiment. The mortality of fish fed on diet A was negligible, the registered growth rate was 313 ± 74 g (124.2%), specific growth rate was 0.32% day^?1 and the food conversion rate was 6.7. The fish fed on diet B (initial weight, 246 ± 74 g; TL, 28.2 ± 2.5 cm) started to feed on day 3 and achieved a total growth rate of about 98% (final weight gain, 241 ± 69 g) and specific growth rate of 0.24% day^?1 (feed conversion rate of 9.00 and mortality 13%). The fish fed on diet C (initial weight, 246 ± 74 g; TL, 28.2 ± 2.5 cm) started to feed on the pellets after 1 month and had a growth rate of 87% (weight gain 214 ± 85 g), a specific growth rate of 0.24% day^?1 and a food conversion rate of 10.6 with considerable mortality (27%). In all three diet groups the fish grew with considerable variation in food consumption and growth rate, depending on seasonal temperature variations of the ambient sea water supplied to the rearing tanks. Chemical analysis showed that the protein level (amount) in the fish meat exceeded 20% in all three fish fillet samples.     

Diet of the Atlantic bonito Sarda sarda (Bloch, 1793) in the Northeast Aegean Sea

Seasonal and size‐related patterns in feeding habits of the Atlantic bonito (Sarda sarda) in the Northeast Aegean were investigated over a 2‐year period May 2007 – May 2009 based on analysis of stomach contents of 134 fish ranging from 266–655 mm fork length. The fish were caught by purse‐seine boats operating around the islands of Lesvos and Chios (Greece). Of the stomachs examined, 46% contained at least one prey item and significant seasonal and size‐related patterns were found in the occurrence of non‐empty stomachs. The overall diet composition in terms of numerical importance was 71% fish, 28% crustaceans and 1% cephalopods. Of the fish, Engraulidae (Engraulis encrasicolus) were the dominant prey taxon, followed by Centracanthidae (Spicara spp.) and then Clupeidae (Sardina pilchardus). Statistically significant monthly variation in diet was apparent, suggesting that S. sarda take advantage of seasonally abundant prey fish in the study area, but no size‐related variation in the importance of the main prey species was detected.