Weight Of Stomach Contents Research Articles

Preslaughter feed withdrawal and sex influences on rabbit physiological response and meat quality

Although preslaughter feed withdrawal is commonly used in the livestock industry to reduce the risk of viscera puncture during evisceration, the optimal feed withdrawal time (FWT) appears to be species dependent and is not yet well defined in rabbits. This study aimed to evaluate the impact of three preslaughter FWTs while considering the effect of sex on physiological response and meat quality of rabbits. Three FWTs (4, 11 and 18 h) were tested using 144 recently weaned Grimaud rabbits fed until they reached an average commercial slaughter live body weight of 2.5±0.2 kg. Rabbits were allocated into 24 cages, with six animals in each cage. Eight cages (four cages for females and four cages for males) were assigned to each of the three FWTs. Blood lactate concentrations measured at exsanguination did not raise concerns related to stress. Female rabbits subjected to 4 h FWT had a higher gastrointestinal tract weight compared to male rabbits and to other females subjected to 11 and 18 h FWT (P=0.04). Stomach content weights were lower after 18 h FWT compared to 4 and 11 h (P=0.002) for both sexes, while caecum weights were not affected by FWT. Caecum pH was higher after 11 and 18 h FWT compared to 4 h (P=0.02). Technological meat quality was not particularly affected by FWT, except for Longissimus lumborum drip loss which was lower for rabbits after 18 h FWT compared to 4 h FWT (P=0.005). With respect to microbiological meat quality, the end of shelf life was reached after 10 days for vacuum-packed hind legs from rabbits after 11 h FWT, as Escherichia coli cell counts for four out of the eight hind legs analysed were higher than 3 Log10 colony-forming units (CFU)/10 g. For the other two FWT groups, the end of shelf life was reached after 15 d, at which point the cell counts for all hind legs were ≥3 Log10 CFU/10 g for E. coli and ≥7 Log10 CFU/g for total aerobic mesophilic and presumptive lactic acid bacteria (the maximum threshold concentrations according to current regulations). Our results demonstrate that when transport (30 min) and lairage (30 min) times are short (1 h in total), an 18-h preslaughter feed withdrawal for both male and female rabbits can allow the gut to empty properly with limited effect on meat quality.

Effects of buccal cavity parasite Ceratothoa carinata (Isopoda, Cymothoidae) on the condition and reproduction of its host fish Japanese scad Decapterus maruadsi.

All species of the isopod family Cymothoidae are obligate fish parasites, extracting nourishment through hematophagy and tissue consumption. To elucidate the detrimental effects of this parasitic relationship upon the host fish, we examined body length, weight of body, gonad, liver and stomach contents, and condition factor of Japanese scad Decapterus maruadsi infected with the buccal cavity parasite Ceratothoa carinata in different seasons. During the host fish's breeding season in July, the wet weight and condition factor of male and female host fish ages 1 and 2 were conspicuously diminished. No impacts were detected in September, after the breeding season. We found no impact of the parasite on the stomach content weight or signs of prey fish in the stomachs. Thus, parasite infection with C. carinata potentially diminishes the reproductive success of the host fish by negatively impacting the host's physiological condition, particularly during the breeding season.

Preslaughter feed withdrawal time and its effect on rabbit blood measures, gastrointestinal tract parameters and Longissimus lumborum glycolytic potential

This study aimed to characterise the physiological response of rabbits to feed withdrawal without stress caused by crating and transport to the slaughterhouse. A total of 72 recently weaned Grimaud rabbits were allocated into 12 cages, each with 6 rabbits (3 females and 3 males, to reflect commercial practices). A preslaughter feed withdrawal time (FWT) was randomly assigned to each of the 12 cages (t=0, 3, 6, 8, 10, 12, 14, 16, 18, 20, 22 or 24 h). Blood lactate and cortisol concentrations were measured at exsanguination. These observations did not indicate an elevated level of stress in the rabbits (P>0.05). The maximum Longissimus lumborum glycolytic potential was observed for rabbits that fasted for 3 and 6 h and was relatively stable from 127.78 to 139.04 μmol/g for rabbits with FWT longer than 12 h. As expected, gastrointestinal tract and stomach content weights were lower for rabbits with longer FWT (P<0.0001), while caecum weights did not (P=0.051). Rabbits with longer FWT had lower stomach pH and higher caecum pH (both P<0.0001). Metataxonomic 16S analysis revealed that FWT had a significant effect (all P<0.01) on microbiome beta diversity in faeces and caecum. The polymerase chain reaction analysis using specific primers revealed Enterobacteriaceae presence in the faeces of male rabbits only at 18 and 22 h. Our results suggest that the caecotrophic behaviour of rabbits allows them to be particularly resistant to hunger despite their small size. However, to limit Enterobacteriaceae shedding, the FWT should not exceed 18 h.

Substantial decline in energy storage and stomach fullness in Antarctic minke whales (Balaenoptera bonaerensis) during the 1990s

A substantial decline in energy storage in the Antarctic minke whale during the 18-year Japanese JARPA research programme (austral summers 1987/88–2004/05) was reported in 2008 (Konishi et al., 2008). The statistical method used in the study was simple multiple linear regression. The results have since been thoroughly discussed by the Scientific Committee of the International Whaling Commission because of the potential importance of the findings. Some had suggested that the sampling heterogeneity in the JARPA data was so substantial that generalised linear models (GLMs) with interaction terms and random-effects terms should be explored. For the present article, five response variables related to energy storage and the variable ‘stomach content weight’ are systematically analysed using GLMs. For all five energy storage variables, the results show declines in the interval 3% to 9% over the JARPA period, all significantly different from zero at the 5% level, but no later decline. The weight of sieved stomach contents declined by 25% over the same period. The coefficients of the decline and the coefficients for most other independent variables were similar to values obtained by simple linear regression, but in some cases the standard errors were larger. The results indicate that important changes took place in the Antarctic ecosystem during the 1990s. It is hypothesised that the most important cause of the changes was the simultaneous increase in numbers of other krill feeders, especially humpback whales.

Pulsed supplies of small fish facilitate time-limited intraguild predation in salmon-stocked streams.

Pulsed supplies of prey generally increase predator food intake. However, it is unclear whether this holds true when predators and pulsed prey are in the same guild (i.e. intraguild (IG) predators and prey). IG prey may increase IG-predator food intake through predation, but they may decrease food intake through competition. To test these hypotheses, we compared the food intake of white-spotted charr (Salvelinus leucomaenis) (IG predator) in streams that were stocked or unstocked with masu salmon (Oncorhynchus masou) fry (IG prey) in streams in Hokkaido, Japan. One day after stocking, mean stomach content weight of charr was six times higher than in unstocked streams due to fry consumption. In particular, large charr showed intense piscivory. However, predation on fry was rare after about three weeks. Some factors that could explain this time-limited IG predation include the growth and decreasing abundance of fry over time and the acquisition of predator-avoidance behaviour. In days other than the first-day post-stocking, food intake by charr did not differ between stocked and unstocked streams. No effects of interspecific competition on charr food intake were observed.

Temporal and Age‐Based Variation in Juvenile Sablefish Diet Composition and Quality: Inferences from Stomach Contents and Stable Isotopes

AbstractPrey communities in the North Pacific Ocean have been disrupted by marine heatwaves, and reductions in forage fishes have had notable impacts on upper‐trophic‐level consumers. Little is known about the potential effects of a changing prey base for some commercially valuable fishes, such as Sablefish Anoplopoma fimbria. The objectives of this study were to evaluate temporal and age‐based shifts in diets of juvenile Sablefish, with a focus on understanding their reliance on high‐quality forage fishes. We collected Sablefish from a bay in Southeast Alaska over 2 years (2017–2019) during their first autumn (September–October; age 0), in late winter (March; age 1), and during their second summer (July; age 1). Pacific Herring Clupea pallasii constituted the majority of the Sablefish diet by weight (82.1%) and by frequency of occurrence (40.7%), with variation among months, years, and age‐classes. Stable isotopes corroborated our interpretation of diet composition from stomach contents and indicated that age‐0 Sablefish sampled in October 2017 relied on more depleted carbon sources than other groups, potentially explained by consumption of adult salmon carcasses. Significant relationships between stable isotope ratios and Sablefish length indicated that size‐based diet composition differences were most prevalent during March and July. Sablefish exploited prey taxa of variable quality (0.02–5.3 kJ/g), but mean energy density of consumed prey differed little among years or months (3.62–4.48 kJ/g). Overall, 21% of stomachs sampled were empty, with the percentage of empty stomachs peaking in late winter (46%). Stomach content weights expressed as a percentage of body weight were highest in autumn 2018, when Pacific Herring comprised over 80% of the diets by weight. Consumption of high‐energy prey, such as Pacific Herring, may contribute to rapid growth of Sablefish during the critical prewinter period. If strong Sablefish year‐classes become more frequent with a warming ocean, they will require substantial prey resources to support their growth to adulthood.

Effects of Age and Sex on Liveweight and Body Composition of the West African Dwarf Sheep

SIXTEEN animals selected from the sheep flock of the University were divided into four age-groups [4, 30, 150-180 and 360-420 days) with each group consisting of two males and two females. They were weighed just before slaughter to obtain their live-weights. Weights of drainable blood, head, hot carcass, trotters, intestinal and stomach contents, liver, kidney, heart, spleen and lungs were recorded and expressed as percentage of the ingesta-free body or empty body weight [E.B.W.]. 
 All body components measured increased in weight with increasing age, but when expressed as percentage of the E.B.W., showed a progressive decrease with advancing age, except the stomach and intestinal contents. The percent moisture content of the visceral organs decreased with advancing age while the percent crude protein and ether extracts increased with age. 
 Sex effects on live-weight and weights of some body components were not apparent at the early age-groups. At maturity however, the males generally had higher values for the various body components. Similarly, the chemical composition of the visceral organs showed very little sex differ ences before maturity; after this stage the males consistently had higher moisture and crude protein values and lower either extracts values than the females.

The forgotten feeding ground: patterns in seasonal and depth-specific food intake of adult cod Gadus morhua in the western Baltic Sea.

This study presents the diet composition of western Baltic cod Gadus morhua based on 3150 stomachs sampled year-round between 2016 and 2017 using angling, gillnetting and bottom trawling, which enhanced the spatio-temporal coverage of cod habitats. Cod diet composition in shallow areas (<20 m depth) was dominated by benthic invertebrate species, mainly the common shore crab Carcinus maneas. Compared to historic diet data from the 1960s and 1980s (limited to depth >20 m), the contribution of herring Clupea harengus decreased and round goby Neogobius melanostomus occurred as a new prey species. Statistical modelling revealed significant relationships between diet composition, catch depth, fish length and season. Generalized additive modelling identified a negative relationship between catch depth and stomach content weight, suggesting reduced food intake in winter when cod use deeper areas for spawning and during peak summer when cod tend to avoid high water temperatures. The results of this study highlight the importance of shallow coastal areas as major feeding habitats of adult cod in the western Baltic Sea, which were previously unknown because samples were restricted to deeper trawlable areas. The results strongly suggest that historic stomach analyses overestimated the role of forage fish and underestimated the role of invertebrate prey. Eventually, this study shows the importance of a comprehensive habitat coverage for unbiased stomach sampling programmes to provide a more reliable estimation of top predator diet, a key information for food web analyses and multispecies models.

What is on the menu? Feeding, consumption and cannibalism in exploited stocks of the jumbo squid Dosidicus gigas in south-central Chile

Only few studies on the feeding and cannibalism behavior of the jumbo squid have been conducted in the Humboldt Current System despite this species is currently considered an important economic resource. It is possible that the diet of this ommastrephid squid varies throughout the year, among areas and body size. Therefore, we herein collected jumbo squids from commercial catches during January to December 2014 using purse-seine nets. The stomach contents were analyzed in terms of frequency of occurrence, number, and weight of prey items. The diet composition was analyzed using Detrended Correspondence Analysis. The variation of jumbo squid diet composition was evaluated from different biological and temporal predictors (sex, maturity, body size and months), considering and analyzing cannibalism. Daily ration was estimated using three methods to calculate consumption and consumption/biomass ratio. Our results suggest that there are significant differences in diet throughout the year, among sizes, and between sexes, however, no differences were found according to the interactions of these factors, except for the interaction between sex and month. In addition, significant differences were detected for each factor (sex, month and body size) when evaluating cannibalism, although these differences were only significant when factors were evaluated independently. Body size was the best predictor of diet composition, richness and cannibalism variation. Stomach content weight was highly biased due to the advanced level of digestion, which in turn biased the diet based on weight, daily ration and consumption analyses. In this sense, the bioenergetic model based on water temperature fitted better than models based on stomach content weight and body mass. These results showed that D. gigas mostly predates on crustaceans and cephalopods, which contrasts with most ecosystem models that suggest that this species highly predates on commercially-exploited fish species.

Impact of warming on the physiological condition of ridged-eye flounder Pleuronichthys lighti during the summer in the central Seto Inland Sea, Japan

Ridged-eye flounder Pleuronichthys lighti is a commercially important flatfish in East Asia. Water temperature has been increasing in the central Seto Inland Sea, Japan, with high levels (> 25 °C) in the bottom layer for 1–2 months during the summer since 1994. To study possible impact of warming on the physiological condition of the flounder, we examined the feeding activity and somatic condition of the flounder monthly from July to November in 1999–2006. Stomach content weight decreased during period with high water temperature > 25 °C from August to September, and physiological condition from August to November. Generalized linear mixed models suggested the negative effects of water temperature on stomach weight, while water temperature did not explain the variability in the physiological condition of the flounder. However, the decrease in relative condition factor from August to September was greater in the year with higher water temperature in this period. These results suggest that high water temperature during the summer in recent years appears to have been unfavorable for the flounder through negative impacts on their feeding and somatic condition.

Comparative morphology and trophic ecology in a population of the polymorphic lizard Sceloporus minor (Squamata: Phrynosomatidae) from central Mexico.

Polymorphism among individuals of the same population has generally been linked to alternative reproductive tactics, where different morphs can exhibit differences in their morphological, ecological, and behavioral attributes. These differences may result in a divergence in diet between morphs due to differential exploitation of habitat, morphological differences that influence prey selection, or differential energy expenditure that results in different nutritional needs. The present study analyzes the morphology (morphometry and body mass) and diet of red and yellow male morphs in a population (El Enzuelado) of the lizard Sceloporus minor from central Mexico. No differences between morphs were found for any of the morphometric variables analyzed (snout-vent length, tail length, jaw length, jaw width, head length, head width, head height, tibia length, femur length, forearm length and ventral patch length). In both morphs, allometric growth was observed in all body features analyzed, as well as in morphometric features of the head across seasons. Analysis of stomach contents showed that the diet of red males was composed of 12 categories of prey, while that of yellow males was composed of 10 categories; those categories of diet not shared between morphs (e.g., Isoptera, Psocoptera) were consumed by their respective morph in very low proportions. Categories of diet with the highest values of food importance for both groups were Coleoptera, Orthoptera, and leaves; a similar pattern was seen across seasons. This, in turn, is reflected in low niche breadth values for each morph and a very high niche overlap. There were no significant differences between morphs overall, or between morphs per season, in the weight and volume of stomach contents or in the number of prey items found in stomachs; however, differences in these variables across all males (independent of morph) were recorded between seasons. Likewise, no significant correlations were found between body size (snout-vent length) and the volume of stomach contents for either morph or between lizard mandibular dimensions and the volume of stomach contents for red morph males. For the yellow morph, prey volume unexpectedly decreased significantly with jaw size rather than increasing as expected. Overall, this study adds new information about the morphology and feeding of males in this species, and suggests that in this population, color morphs lack the morphological and ecological differences found in some other species of polymorphic lizard.

A Study on Some Biological Aspects of Giant Snakehead Fish (Channa micropeltes) in Huai Suea Ten Wetland Site in Thailand

This research was aimed to study on biological aspects of giant snakehead fish (Channa micropeltes) in Huai Suea Ten wetland site, Nam Phong District, Khon Kaen Province in Thailand between April, 2017 and March, 2018. Thirty-six fish species belonging to 17 families were observed at 10 sampling sites. Three Channidae fishes, namely snakehead fish (Channa striata), giant snakehead fish (Channa micropeltes), and forest snakehead fish (Channa lucius), belonging to the family Channidae were reported. A total of 230 giant snakehead fish were found in this survey which consisted of 118 males and 112 females. The sex ratio (male: female) was 1:0.95. The gonadosomatic index value of the female (0.79±0.05%) was higher than that of the male (0.25±0.08%). The body length and body weight of a total of 230 giant snakehead fish observed in this study showed the average of a total body length was 43.71±11.72 cm; and the average of the body weight was 448±173 g/fish. The condition factor of giant snakehead fish observed in 12 months were in a range of 0.45-0.74 for the male and 0.39-0.70 for the female. The ratio of the body and intestinal length of giant snakehead fish was as 1: 0.70. The stomach digesta components, expressed as the percentages of a whole stomach content weight of this fish species consisted of 51.8% of fish fillet, 30.3% of small fish and 17.9% of digested digesta.

Grazing management affects fish diets in a Wadden Sea salt marsh

Salt marshes provide favourable feeding conditions for fish thanks to a variety of food sources including terrestrial prey, which can be negatively affected by livestock grazing. We evaluated the seasonal effect of sheep grazing on fish diets in a Wadden Sea salt marsh. Consumed quantities and frequencies of terrestrial prey differed between predators. While terrestrial prey was unimportant for herring and sand goby, common goby and three-spined sticklebacks consumed it immediately during winter, when it became available through marsh flooding. In contrast to the relative stomach content weights, the stomachs content compositions differed between grazing treatments. Sticklebacks consumed terrestrial prey more often and in higher amounts in the ungrazed than in the grazed marsh. Using random forest models, the importance of grazing management for fish compared to other influencing factors was analysed based on sticklebacks. Its most important terrestrial prey was the energy-rich and probably easy to catch amphipod Orchestia gammarellus. Both the ratio of fishes feeding on Orchestia and the consumed amount of Orchestia depend mainly on the accessibility, determined by the flooding height and duration. The abundance of Orchestia was the second most important factor determining its consumed amounts. Orchestia densities are significantly reduced by sheep grazing. Therefore, sheep grazing has a negative impact on fish feeding opportunities in winter, when marine prey on the tidal flats is scarce. To improve the feeding habitat value of Wadden Sea salt marshes for fish it is advisable to keep lower elevated marshes with large creeks ungrazed.

Food habits of bluegillLepomis macrochiruspopulations in reservoirs in Kagawa, Japan

Food habitats of bluegill Lepomis macrochirus populations in Hachiman and Saburo Reservoirs, Japan, were examined. In both populations, stomach content weights reduced relative to an increase in body weight, there being no gender-specific differences. However, relative stomach weights of males were significantly greater than those of females, a sexually dimorphic characteristic of bluegill. Feeding amounts of bluegills in Hachiman Reservoir tended to be low in winter–spring, and high in summer–autumn. Stomach contents, including insects, zooplankton, crustaceans, fishes, plants and inorganic debris, showed highly generalized feeding, although insects were frequently taken, particularly during spring–summer, with chironomids being a principle dietary item. In spring, numerous eggs of the crucian carp were ingested, suggesting a significant impact upon reproduction of the latter. In summer, many bluegill stomachs were filled with green algae. However, similar cramming of the intestinal tract suggested no digestive ability of bluegill for plant materials, including algae. In both habitats examined, the stomach contents of small bluegills (ca. 20–50 mm TL) comprised almost entirely zooplankton, diets subsequently diversifying gradually with growth. The almost complete absence of zooplankton in bluegills greater than ca. 110 mm in TL indicated a growth-related food habit shift from planktivory to omnivory.

How do season, on-farm fasting interval and lairage period affect swine welfare, carcass and meat quality traits?

This study was carried out in order to determine the effects of different combinations of on-farm fasting intervals (8, 12, 16, 20h) and 1.5h of transport plus lairage periods (1, 3, 6h) at different seasons (summer/winter) on blood stress parameters (cortisol and lactate), stomach content and weight, skin lesion and meat quality in a total of 960 pigs from eight farms. Blood lactate levels were greater in the summer (P < 0.001) and stomach content was affected (P < 0.05) by season, on-farm fasting interval (P < 0.001), lairage time (P < 0.0001). Stomach content weight reduces as the total feed withdrawal time increases up to on-farm fasting of 17 and 1h of lairage. Stomach content can be influenced by feed and water in different ways according to treatments. Only 8h of on-farm fasting is not enough to empty stomachs from feed content. However, an on-farm fasting period of 16h or longer can also increase the occurrence of more water in the stomachs. Carcass lesions caused by fighting were greater (P ≤ 0.005) in the winter, mainly after 3 and 6h of lairage (P ≤ 0.005). Loin and ham pHu was lower (P ≤ 0.05) for pigs slaughtered after 6h of lairage during the summer. The application of 12h of on-farm fasting with 6h of lairage seemed to be best combination to reduce stomach content weight (feed and water). In the winter, shorter lairage period can be used to reduce percentage of skin lesions and better pork quality traits in pigs.

ANALISIS DEL CONTENIDO ESTOMACAL DEL CAMARON TITI Xiphopenaeus kroyeri (HELLER) (CRUSTACEA: NATANTIA: PENAEIDAE)

Juveniles and adults of the seabob Xiphopenaeus kroyeri (Heller) were collected at monthly invervals between September 1988 and June 1988. The food items were determined in order of descending importance as: detritus and fragments of bivalve shells, polychaete worms, foraminiferans, and crustaceans. There was a difference in the feeding habits between the rainy seasson (September to December) and the dry season (January to June) with items like rotifers, sponges and radiolarians appearing only during the dry season. Analysis of the frequency of occurrence of different food items showed that groups like rotifers and bryozoans appear more frequently in juveniles. Measurements of protein and carbohydrate levels in the stomach contents revealed the highest peaks of proteins for adults in September (92.03 ug/mg dry weight of stomach contents) and for juveniles in December (81.27 ug/mg), and of carbohydrates for adults in October (45.81 ug/mg) and for juveniles in December (35.25 ug/mg). Quantitative differences in proteins and carbohydrates between the two size groups were not statistically significant.

Sex differences in the composition of the natural diet of Panulirus argus (Decapoda: Palinuridae) in the eastern of the Gulf of Batabano, Cuba

The spiny lobster Panulirus argus is one of the most valuable fishery resources in the Caribbean Sea. This is the only species of lobster that has commercial importance in Cuba. This study was aimed to identify the organisms that conform the natural diet for both sexes of P. argus and to determine the importance of each prey in the diet of each sex. A total of 30 stomachs of commercial lobsters (≥ 76mm of carapace length) was analyzed. The identified content was grouping by items and classified for species if it was possible. The total weight of each item was determined and the gravimetric method was applied to estimate the relative weight of the principal diet components. The most frequently consumed prey was also determined. Items with high, middle or low importance were established by the relative importance index (IIR). Similarities between both sexes diet were estimated by similarity index (ISe). Stomachs were extracted of lobsters captured in a fishing zones from eastern of the gulf of Batabano. The predation pressure (P) on the mollusks species found in the stomach content was calculated based on the respective opercula. It was possible to identified 15 feeding entities (12 in females and 14 in the males) being the preferences: crustacean rests (100%), shell rests (80%), vegetable rests (70%), opercula (63%) and mineral rests (53%). Those preference entities were the same between sexes although in the males the foraminifera and the mineral rest were included. The IIR showed crustaceans as a single group of high importance. The gravimetric analysis showed crustaceans as the most consumed prey (62.3% in females and 40% in males). The opercula of Lobatus gigas, Turbo castanea, Fasciolaria tulipa, Nassarius antillarum, Cerithium sp and Tegula fasciata were found. Tegula fasciata showed the highest predation pressure (2.25 in females and 2.14 in males) and together Cerithium sp. they were the most abundant species (60.5% and 33.9% respectively). Respect to the weight of stomach contents the Mann-Whitney test showed no significant difference between females and males. The diet of both sexes of P. argus in the assessed area was similar (ISe=96.75%) and it was constituted mainly of crustaceans and mollusks.

Feeding ecology of mackerel and dietary overlap with herring in Icelandic waters

ABSTRACTThe Northeast Atlantic mackerel (Scomber scombrus) has been extending its summer feeding distribution north and west, including around Iceland, since around 2006. The objective of this study is to quantify the weight gain and total food consumption of mackerel and to evaluate the food competition between mackerel and herring (Clupea harengus) feeding in the marine ecosystem around Iceland during the summers 2009–2011. Mackerel feeding in Icelandic waters gained around 43% on average in weight during these summers. Based on swept-area abundance estimates of mackerel from an international survey in 2011 and available estimates of food conversion efficiency in mackerel, the weight gain in Icelandic waters in 2011 corresponded to a total consumption of around 3.4 (2.4−4.5) million tonnes. Overall, 98% of 2314 mackerel, 91% of 398 Icelandic summer-spawning herring and 96% of 424 Norwegian spring-spawning herring stomachs, collected over the summers 2009−2011, contained food. The mean weight of the stomach content of mackerel was higher than for herring in all the years. While the stomach content weight of mackerel was generally highest in southeastern and southwestern areas, it was highest for herring in western, eastern and northern areas. Analysis of stomach contents showed that Copepoda were the most important food of mackerel in most areas, while Copepoda and Euphausiacea were the most important food items for herring. Fish prey contributed a higher proportion in stomachs of mackerel than herring, although relatively low for both species.

Trophic ecology of Mugil liza at the southern limit of its distribution (Buenos Aires, Argentina)

AbstractIn order to get to know the habitat and feeding habits of Mugil liza on the southern coast of Buenos Aires province, 65 specimens obtained at two sampling sites - the San Blas bay (SBB) and the mouth of the Quequén-Salado river (QSR) - during spring (November 2012) and summer (February 2013) were analyzed. Specimens were measured, sexed and weighed, their stomachs were removed and their stomach contents weighed and analyzed under the stereoscopic microscope. The specimens were adults, 28-49 cm in length and weighing 380-1100 g. Population growth was higher in the SBB (TW: 0.003*TL3.36), than in RQS (TW: 0.045*TL2.61). About 98% of the stomachs had some content, their repletion rate being of between 0.4 and 1.2%. About 75% of the stomachs contained very fine sand with few benthic organisms (algae, copepods, foraminifera), whereas the remaining 25% of stomachs contained coarse sand and a greater presence of benthic fauna (amphipods, bivalves, gastropods and coral organisms). The linear relationship between the weight of stomach contents and the total weight and length of the fish showed that the rates of growth (slope) were the same at both sites, but intercept values were significantly higher for San Blas bay (test parallelism; p &lt; 0.001).

Diel feeding patterns and daily food intake of juvenile stone flounder Platichthys bicoloratus

Pleuronectid flatfish are considered visual day feeders, but their ability to feed at night has not been examined in the field. Juvenile (age-0) stone flounder Platichthys bicoloratus were collected, and their stomach contents were investigated in situ every 4h over a 24-h period in an estuarine habitat to elucidate diel feeding periodicity. The weight of juvenile stomach contents was usually the highest around dusk and the main prey was bivalve siphons. To reveal whether juveniles feed only at particular times during the day or throughout a 24-h period, we conducted 24-h cage experiments in which 10 juveniles with empty stomachs were held in a cage for approximately 4h (six trials). This experiment was carried out three times during different moon phases. Juveniles primarily ingested prey during the day, but 30% of fish that were caged at night also ingested prey. The number of successful captures by the caged fish was much greater during the day than that at night. These results indicate that stone flounder generally feed during the day and they may only feed at night under unusual situations, although they have the ability to capture prey at night. The mean daily ration estimated by diel changes in stomach content weight varied from 3.4% (95% confidence interval, 1.8–4.8%) to 13.2% (11.0–15.6%) of body weight between survey dates, indicating that daily food consumption by fish estimated from a single survey may be strongly biased.