Stomach Fullness Research Articles

Impacts of a Changing Ecosystem on the Feeding and Feeding Conditions for Atlantic Salmon During the First Months at Sea

During the last decades, many wild Atlantic salmon populations have declined dramatically. One hypothesis for an observed reduction in salmon marine growth and survival is reduced abundance of prey. However, the effect of spatial and temporal variation in marine prey abundance on post-smolt feeding conditions is poorly understood. Here we use stomach content data from 2572 salmon post-smolts sampled during 25 years in the Northeast Atlantic Ocean to examine spatial and temporal changes in diet and stomach fullness. Sandeel larvae west of Scotland and Ireland and in the northern North Sea, herring larvae in the eastern part of the Norwegian Sea, and amphipods in the western part of the Norwegian Sea were particularly important prey species. There was a reduction of fish larvae in the post-smolt stomachs over a large geographic area when comparing the period 1995–2004 to 2008–2019. This may be result of a bottom-up driven process, as increasing extent of Arctic Water masses and zooplankton abundance were positively correlated with post-smolt stomach fullness in the Norwegian Sea. Furthermore, the interspecific competition for fish larvae between post-smolts and mackerel may have increased with a larger mackerel stock expanding the feeding migrations northwards since 2007.

Spatial Variability of the Feeding Conditions for the Norwegian Spring Spawning Herring in May

The abundant and ecologically important copepods Calanus finmarchicus and Calanus hyperboreus within the Norwegian and Iceland Seas are key prey species of Norwegian spring spawning herring. The volume flux of East Icelandic Water, which carries the mentioned zooplankton species into the southern Norwegian Sea, is highly variable. The years 1996–2002 have previously been characterized as high influx years, 2003–2016 as low influx years and since 2017 a reversal to higher influx has been apparent. Hydrographic and zooplankton data, as well as fish data on herring (size and diet content), from the International Ecosystem Surveys in the Nordic Seas in May have been used in this study. Focus is on the south-western Norwegian Sea, where herring has regularly been observed in May since 2005 and where changes in plankton availability and in the hydrographic environment have also been observed. Diet biomass from 2017–2020 (higher influx period) showed higher stomach fullness compared to 2007–2011 (lower influx period). Furthermore, the highest stomach fullness is observed in the westernmost feeding region—referred to as the Feeding Spot. The scrutinized diet content showed a notably higher biomass of ingested C. hyperboreus in 2020 compared to 2007–2011, indicating a preference for the larger and more nutritious copepod. Zooplankton analysis from May 2020 revealed that the core of the western feeding region, i.e., the area with highest zooplankton biomass, was located within the subarctic waters immediately north/west of the junction between the Iceland-Faroe Front and the Jan Mayen Front. The core area was mainly represented by overwintering stages and the derived adult stages of C. finmarchicus and C. hyperboreus. Interplay between food availability and accessibility, in terms of temperature, to the Feeding Spot, is discussed.

Feeding ecology of Neoarius leptaspis in the Rawa Biru Lake, Merauke, Indonesia

Abstract. Wibowo DN, Rukayah S, Wahayu NL, Mote N. 2022. Feeding ecology of Neoarius leptaspis in the Rawa Biru Lake, Merauke, Indonesia. Biodiversitas 23: 1327-1335. A few studies have been carried out on Neoarius leptaspis (Bleeker, 1862), however, its feeding ecology was not examined, especially for the sample from Rawa Biru Lake, Merauke, Papua, Indonesia. Therefore, this study aims to analyze the feeding ecology of N. leptaspis at 8 sampling sites in the lake, which were sampled in the morning and evening. The parameters observed were natural food diversity, mouth width ratio, intestine length ratio, stomach fullness and content, preponderance index, and electivity index. The result showed that 25 plankton species were observed in the waters. Neoarius leptaspis has a mouth width ratio of approximately 75% of head width. The full stomach was observed in the samples collected in the evening, where the diets were dominated by animal materials as indicated by the indexes of preponderance and electivity. The mouth width ratio, feeding periodicity, intestine length, and dominant diets were similar to the previous reports on the same species from other regions. This showed that N. leptaspis is a predatory fish species based on the feeding ecology data, which provides essential information for fisheries and conservation.

Winter ecology of specialist and generalist morphs of European whitefish, Coregonus lavaretus, in subarctic northern Europe.

European whitefish is a model species for adaptive radiation of fishes in temperate and subarctic lakes. In northern Europe the most commonly observed morphotypes are a generalist (LSR) morph and a pelagic specialist (DR) morph. The evolution of a pelagic specialist morph is something of an enigma, however, as this region is characterized by long, dark winters with pelagic primary production limited to a brief window in late summer. We conducted the first winter-based study of polymorphic whitefish populations to determine the winter ecology of both morphs, and we combined seasonal diet and stable isotope analysis with several proxies of condition in three polymorphic whitefish populations. The generalist LSR morph fed on benthic and pelagic prey in summer but was solely reliant on benthic prey in winter. This was associated with a noticeable but moderate reduction in condition, lipid content and stomach fullness in winter relative to summer. In contrast, the DR whitefish occupied a strict pelagic niche in both seasons. A significant reduction in pelagic prey during winter resulted in severe decrease in condition, lipid content and stomach fullness in DR whitefish in winter relative to summer, with the pelagic morph apparently approaching starvation in winter. We suggest that this divergent approach to seasonal foraging is associated with the divergent life-history traits of both morphs.

Comparisons of Soybean and Wheat; in the Focus on the Nutritional Aspects and Acute Appetite Sensation.

Soybean flour is often used as a gluten-free ingredient. We aimed to compare the nutrients and the difference in satiety of soybean and wheat after ingestion. We measured the amounts of polyphenol and oxygen radical absorbance capacity (ORAC) and examined the acute appetite sensation after the ingestion of soybean powder and bread powder. Japanese women were enrolled in the meal tests. Participants were provided with 18 g of bread or soybean powder, 180 g of yogurt, and 285 mL of bottled water. Subjective satiety (hunger, appetite, satiety, and stomach fullness) was measured using a visual analog scale 120 min after sample ingestion. The polyphenol content and ORAC were 2- and 12-folds higher, respectively, in soybean powder than in bread flour. In the meal tests, the area under the curve (AUC) of satiety 60–120 min after ingestion (n = 44) was significantly higher for soybean powder than bread powder. The AUCs of hunger and appetite 60–120 min after ingestion were significantly lower for soybean powder than bread powder. The effect sizes of hunger and appetite by soybean powder were 0.341 and 0.424, respectively. Thus, these results suggest that soybean is a healthy food and soybeans maintain satiety and suppress hunger more than bread flour.

Food and Feeding Biology of Nile Tilapia (Oreochromis niloticus) in Lake Langeno, Ethiopia

This study aimed to investigate the natural feeding behavior of Nile tilapia in Lake Langeno, Ethiopia, with emphasis on potential spatial, size and seasonal effects on ingested food items. This study of the food and feeding biology of O. niloticus in Lake Langeno, Ethiopia, was conducted from March 2016to February 2017. Fish samples were collected monthly from six different sampling sites using different mesh sizes of gillnets. A total of 610 fish specimens with full stomachs were considered for the assessment of feeding biology. In total, seven food items, namely phytoplankton, zooplankton, insects, detritus, macrophytes, fish parts and nematodes, were identified from the fish stomach contents. Phytoplankton was the most commonly consumed food prey, followed by detritus, zooplankton and macrophytes. The other food items were occasionally and randomly consumed. Phytoplankton and detritus were the dominant food prey in the dry season, with zooplankton and macrophytes the main prey during the wet months. The contribution of phytoplankton, zooplankton and insects were slightly highest in small-sized groups (<10 cm), whereas detritus, macrophytes and fish parts were highest in larger-size groups (>20 cm) (p < 0.05). The present results point to a concurrence of the relative importance of dietary items at the individual level, species level and among the study sites. Phytoplankton was the primary consumed food item, which indicates the specialist feeding strategy of Nile tilapia in the lake. Generally, food items of plant origin, typically associated with less protein content than animal origin food items, dominated the stomach contents of Nile tilapia. The dietary pattern of Nile tilapia in Lake Langeno shifts with size and season, aspects that might warrant further study in view of aquaculture applications as well as climate change.

Feeding habit of Brown trout (Salmo trutta fario) in upper parts of river Swat, Pakistan.

Salmo trutta fario is the most important fish species of family Salmonidae inhibited in cool waters all over the world including the nortern parts of Pakistan. This study was aimed to find out the prey selection and feeding habits of the species. One hundred and eighty five Salmo trutta fario were captured from March 2016 to April 2017. Feeding intensity as represented by a fullness index (FI), changing with various length groups and season. Out of 185 Brown trout 24 fish stomaches were found empty. The most important and common food items of brown trout were Brachycentridae, Blepharocera, Hydropsychidae, ephemerella spp. Kruskal Wallis H-test were applied on feeding intensity groups consisting of three month group. The test statistic for K.W-H-test were (H=8.13 with df =3) had a p-value of 0.043 < (alpha=0.05 indicates favor of the alternative hypothesis of at least one difference among the feeding intensity groups. The linear relationship of N with index of relative importance and %IRI denoted by least square regression line (N = 35.2 + 22.1%IRI), shows that for 22 prey there is 1% change in IRI. The relationship between total length (mm) and fish body weight (gm) is expressed by Pearson correlation coefficient (r = 0.976), showed that total length (mm) and fish body weight (gm.) is highly correlated. Descriptive statistics are used for the stomach fullness, which shows that feeding intensity was recorded higher from March to May. A total of 2289 preys was recorded including the most common were; Trichoptera, Hydropsychidae, Brachycentridae, diptera, blepharocera, ephemerala, chironomida, honey bees, grass hopper, locust, trout egg, trochanter, plant tissue, stones were retrieved from the gut contents of brown trout. According to index of relative importance IRI% four preys represents major components of the diet. The highest IRI% was recorded in Brachycentridae (39.38%), followed by blepharocera (13.23%), Hydropsychidae (10.76%) and ephemerella spp (8.28%). The relationship between IRI and FO is (r =0.556) is moderately correlated with coefficient of determination (r2=0.31). This study will help in the development of an artificial diet for the species for better growth performance in captivity.

Deep-Water Japanese Blunthorn Lobster Palinustus waguensis Kubo, 1963: First Estimates of Life History Parameters From the Southwest Coast of India

Palinustus waguensis Kubo, 1963, is the deep-sea Japanese blunthorn lobster belonging to the Family Palinuridae. It is a species that has been rarely reported, living in rocky habitats on deep-reef slopes at a depth of 100–250 m. An estimated catch of 100 kg of P. waguensis consisting of 113 males, 54 females, and 23 berried lobsters were collected during the first fortnight of January 2019 from the multi-day shrimp trawls operating off Sakthikulangara, Kerala, India. The mean total length was recorded as 112.3 mm in males, 102.6 mm in females. The parameters of the length-weight relationship were estimated as, a = 0.041, b = 2.84 for males and a = 0.05, b = 2.86 for females, which were not significantly different (P &gt; 0.05, r2 &gt; 0.90) between the males and females. The relative condition factor (K) in the males and females of P. waguensis ranged from 2.07–4.96 and 1.87–3.86, respectively, attributing to the better feeding efficiency in males. Food and feeding analysis revealed the dietary content as fish (53 %), crab (23.5 %), shrimp (7.8 %), digested matter (11.6 %), and foraminifera (4 %). Feeding intensity analysis about the fullness of the stomach showed the specimens bearing full stomachs (11.3 %), three-fourth full (9.9 %). Length at 50 % maturity (Lm50) was 96.9 mm. Gonado-somatic index (GSI) ranged from 3.39 to 8.13. The present study forms the first report on the biology of the deep-water Japanese blunthorn lobster, P. waguensis from India.

Особенности питания окуневых рыб в малом озере на водосборе Онежского озера

Fish feeding process is studied as one of the links in the transformation of the energy of a water reservoir, as one of the factors that determine the ecology of fish and make an imprint on the morphology, physiology and behavior of fish, or as one of the criteria, which help the most rationally use natural resources of the water bodies. The results of work carried out by the Northern Water Problems Institute (NWPI KarRC RAS) and Petrozavodsk State University (PetrSU) within the framework of state assignments, forecast problems and economic contractual topics on assessing the nutrition of perch species (perch, ruff) in some lakes of the Konchezero group (South Karelia), in particular Lake Munozero, which is part of the lower reaches of the river Shuya belonging to the catchment area of Lake Onega. The work was carried out by the experts from the IWPS KarRC RAS and PetrSU in 2018-2020. Its main hydrological and ichthyological indicators have been studied. The reconnaissance fish productivity of Lake Munozero based on the development of the forage base at the present stage is estimated as 9 kg/ha. The feeding spectra of ruff and perch in the lake overlap only with respect to eggs, the ruff using eggs more actively. Predation is peculiar only to perch, while even fish whose size is less than 14 cm (the average size of the transition to predation for Karelia) hunt at a time when there is a lot of other food in the reservoir. As the perch passes to summer feeding, its diet becomes more diverse. Some benthic organisms are replaced by others, an air fraction appears, the perch's diet includes fish in summer and spring; nutrition becomes more active: the average stomach fullness index increases from 7.3 to 145.6‰.

Ontogenetic diet shifts and feeding dynamics of Trichiurus japonicus Temminck & Schlegel, 1844, off Guishan Island, Southern East China Sea

Trichiurus japonicus Temminck & Schlegel, 1844, is one of the most ecologically and economically important fish species in the waters of southern East China Sea. Species caught by trawlers operating in the surrounding waters of Guishan Island, southern East China Sea were collected regularly from March 2018 to February 2019. The stomachs of 434 hairtails ranging in total length (TL) from 100 to 1090 mm were analyzed to study their feeding habits. Diet composition and seasonal changes in prey items were analyzed over 12 months (2018–2019) to detect any feeding shifts in prey items. Feeding indices, namely Index of Relative Importance (%IRI), Gastro-somatic Index (GaSI), Empty Stomach Ratio (ESR), and Stomach Fullness Index (SFI), were calculated to determine the feeding habits, seasonal changes, and ontogenetic shifts in prey items. ESR values differed significantly across hairtail size groups. However, no significant variations were found in ESR values between the sexes and season. The diet of T. japonicus comprised fish (80.07%), shrimps (13.89%), cephalopods (0.61%), and miscellaneous items (5.43%). Benthosema pterotum was the most common prey item during the research period, followed by Myctophidae spp and Sergia lucens. The vacuity index (VI) of T. japonicus was 29.26 percent, indicating that it is a carnivore with a relatively edacious. An unidentified teleost, as well as shrimp remains, was observed in the form and was grouped as miscellaneous items. Juveniles of Trichiurus sp. were noticed occasionally in the gut, indicating the cannibalistic behavior of T. japonicus.

Awareness of Fluid Losses Does Not Impact Thirst during Exercise in the Heat: A Double-Blind, Cross-Over Study.

Background: Thirst has been used as an indicator of dehydration; however, as a perception, we hypothesized that it could be affected by received information related to fluid losses. The purpose of this study was to identify whether awareness of water loss can impact thirst perception during exercise in the heat. Methods: Eleven males participated in two sessions in random order, receiving true or false information about their fluid losses every 30 min. Thirst perception (TP), actual dehydration, stomach fullness, and heat perception were measured every 30 min during intermittent exercise until dehydrated by ~4% body mass (BM). Post exercise, they ingested water ad libitum for 30 min. Results: Pre-exercise BM, TP, and hydration status were not different between sessions (p > 0.05). As dehydration progressed during exercise, TP increased significantly (p = 0.001), but it was the same for both sessions (p = 0.447). Post-exercise water ingestion was almost identical (p = 0.949) in the two sessions. Conclusion: In this study, thirst was a good indicator of fluid needs during exercise in the heat when no fluid was ingested, regardless of receiving true or false water loss information.

Diet and feeding behaviour of albacore Thunnus alalunga in the western Mediterranean Sea during the spawning period.

Mature albacore tuna (Thunnus alalunga) are expected to have high energy requirements at the time of breeding. However, there are no descriptions of the diet of albacore in the Mediterranean Sea that can help us to understand if such requirements can be obtained from feeding during reproduction. In this study, we analysed the stomach contents of reproductively active albacore captured from 2010 to 2015 in the oligotrophic waters of the western Mediterranean Sea, one of their main spawning grounds. Estimates of stomach fullness revealed intense feeding activity, and prey composition indicated important consumption of mesopelagic fish, including barracudinas, myctophids and small pelagic crustaceans. Plastic debris occurred in 25%-53% of the stomachs sampled across all years. Prey composition was not different between males and females. However, females fed at higher rates and had higher hepatosomatic index values than males, suggesting that increased feeding could contribute to meet their higher energy demand associated with offspring production. We observed a diet shift from small crustaceans to fish prey along fish size. During the spawning period, albacore showed a specialist feeding behaviour by preying on aggregations of vertically migrating myctophids and small crustaceans, probably when they were near the surface. This study provides information and biological data to support ecosystem modelling and to increase the understanding of albacore ecology.

THREE SPOT GOURAMI (Trichogaster trichopterus) FOOD HABITS IN THE KOMERING RIVER'S DOWNSTREAM, SOUTH SUMATERA

One of the downstream areas of the Komering River with potential for capture fisheries is Sungai Dua Village. One of the types of fish caught by fishermen in Sungai Dua is the three spot gourami (Trichogaster trichopterus). The three spot gourami fish is a type of freshwater consumption fish that has high economic value. But the fishes only rely on catches from nature. If the fishing is carried out continuously, without domestication and cultivation, it will cause a decline in the fish population. The research about the biological aspects of red-eye septic fish (Trichogaster trichopterus) which include food habits, relationship length and weight, condition factors and stomach fullness index. This research was conducted from April to June 2017. Sampling was carried out in the downstream waters of the Komering River in Sungai Dua Village, Banyuasin Regency, South Sumatra. Fish samples were analyzed at the Animal Taxonomy Laboratory, Department of Biology, Faculty of Mathematics and Science, Sriwijaya University. The determination of stations in sampling was carried out using multiple sampling methods, namely purposive sampling and quota sampling. The result of this research showed that (1) the Cyanophyta is the main food for the three spot gourami, Diatomae and Desmidiacae as a complementary food, while the additional foods are Rhizopoda, Chlorophyta, Ostracoda, and Entomostraca, (2) The growth pattern of red-eyed fish is negative allometric with a b value of -2 (b &lt;3), the increase in length is faster than the weight gain, (3) The highest condition factor value is found in the size range 6.01-7.00 cm of 23.25 gr / cm and the lowest condition factor value is in the size range 5.01-6.00 cm of 0.62 gr / cm, and (4) The highest hull fullness index value of the red eye sepat fish hull is in the size range 7.01-8.00 cm at 32.86% and the lowest hull fullness index value at the size range 8.01-9.00 cm is 2.05% .

Diet composition, feeding dynamics and proximate composition of obtuse barracuda Sphyraena obtusata (Cuvier, 1829) in the southeastern Arabian Sea

The feeding dynamics and nutritional value of obtuse barracuda, Sphyraena obtusata collected from the coastal waters of Karnataka, southeastern Arabian Sea, India, were investigated between August 2019 to March 2020. Three hundred and fifty five specimens of obtuse barracuda having 16.5–30.1 cm total length and 23.63–175.27 g total weight were analyzed. Of the analyzed stomachs, 119 stomachs (vacuity index = 33.52%) were empty. The high feeding intensity was observed during March with 32.43% fishes having full stomachs. Stomach fullness index values were significantly (p < 0.05) higher during November (2.46 ± 0.44) and March (2.46 ± 0.41). The most dominant prey item in terms of frequency (87.80%), number (57.63%), volume (91.82%), and % IRI (93.76%) was teleosts. Crustaceans and cephalopods were encountered less frequently and were represented by Acetes sp. and Uroteuthis duvauceli respectively. The high protein (21.39 ± 0.52%) and fat (1.21 ± 0.33%) content recorded during March resulted in high-energy value (102.11 ± 5.20). The information on dietary composition and nutritional value of obtuse barracuda provided in this study can be useful for sustainable management of the fish stock in the Karnataka coast. The high protein and energy content indicated that this fish may be considered as highly nutritive food for a healthy diet.

Examination of the Trexler-DeAngelis Model of Maternal Provisioning Reveals That Matrotrophy Is Costly

The evolution of matrotrophy (post-fertilization maternal provisioning to developing embryos) has been explained through several hypotheses. Trexler and DeAngelis proposed in 2003 a theoretical model that defines the ecological conditions under which matrotrophy would be favored over lecithotrophy (pre-fertilization maternal provisioning). According to this model, matrotrophy offers a selective advantage in environments with abundant and constantly available food, whereas environments with limited and fluctuating food resources should instead promote a lecithotrophic mode of maternal provisioning. This model also proposes that matrotrophy entails the consequence of leaner reproductive females and in turn shorter lifespans. In this study, we examined the Trexler-DeAngelis model using data from 45 populations of five viviparous species from the fish genus Poeciliopsis (family Poeciliidae). We used the matrotrophy index (MI) as a measure of post-fertilization maternal provisioning, and the index of stomach fullness and individual body condition (BC) as proxies for food availability. We also estimated the magnitude of fluctuations in food availability by calculating the temporal variances of these two proxies. Neither abundant nor constantly available food were associated with greater degrees of matrotrophy, which fails to support the predictions of the Trexler-DeAngelis model with respect to the ecological drivers of increased post-fertilization provisioning to embryos. Nonetheless, in all five species we observed that females with greater degrees of matrotrophy had poorer BC compared to females that provided less nutrients to embryos after fertilization. This finding is consistent with one of the expected consequences of advanced matrotrophy according to the Trexler-DeAngelis model, namely, a detriment to the nutritional status of females. Our study provides compelling evidence that gestating females experience a trade-off between post-fertilization provisioning to embryos and self-maintenance, revealing in turn that matrotrophy is a costly reproductive strategy.

Beyond Metoclopramide for Gastroparesis

Beyond Metoclopramide for Gastroparesis

Morphological investigation of canine epigastric organs and adjacent structures via computed tomography, ultrasound and anatomical prosection

The canine epigastric organs, their locations and visualization of these components are essential for veterinary practice and anatomical research. Despite their importance, conflicts and discrepancies in the published material, to date, still exist, even in a species that has been studied extensively. The aim of this research was to undertake computed tomography, and anatomical sections from differing views and levels in addition to the ultrasound appearance of the main organs of the epigastria region. The epigastric organs, and associated anatomical features and landmarks that affected by stomach fullness were described in relation to their relative positions, visual appearance and general anatomy for both empty and filled stomachs. These features were not only described, but also compared against the published literature.

Observations on the trophodynamics of sawtooth barracuda,Sphyraena putnamaefrom the Bay of Bengal, northern Indian Ocean

AbstractMarine capture ofSphyraena putnamaealong western Bay of Bengal has been increasing. Owing to scarcity of information available on feeding dynamics globally, the present study was conducted using 763 individuals captured during 2017–19, to decipher trophic ecology and relationships. Of the individuals analysed, 54.8% had their stomachs either empty or with trace amounts of food, 27.3% had part-full stomachs and 18.0% had full stomachs. Stomach vacuity and fullness as well as predator–prey weight ratio varied with increase in body size, implying higher feeding intensity in large-sized fishes. Feeding activity was highest during July–November and lowest during March–April. The species is an opportunistic piscivorous pelagic predator that feeds on teleosts (&gt;85%) and cephalopods. Sardines were the major prey, followed by whitebait, squid, bigeye scad, Indian scad, silverbellies and Indian mackerel. Diet contents were similar between sexes (82.17%); however, it varied among seasons (56.86–69.85%). Shifts in prey preferences from sardines, squid and bigeye scad to ribbonfish, shad, grunter, Indian mackerel, horse mackerel andAceteswere observed with increase in fish size, and diet varied between individuals sized &lt;60.0 and &gt;60.0 cm. Trophic level value was 3.51 ± 0.13 and Levin's Standardized Niche Breadth Index was 0.21. Dietary niche breadth varied across seasons and sizes, with higher values during summer and winter (0.36–0.41) and in fish measuring &gt;45.0 cm (0.50–0.68), which implies generalized feeding behaviour. The present study represents the first detailed report on the diet ofS. putnamaeand will provide a substantial contribution to stock management through understanding of trophic interactions.

Poor feeding opportunities and reduced condition factor for salmon post-smolts in the Northeast Atlantic Ocean

AbstractDuring the last few decades, many wild Atlantic salmon populations have declined dramatically. One possible contributing factor for the decline is reduced prey availability at sea. Here, we examine post-smolt diet and investigate if post-smolts show signs of selective feeding based on 2546 post-smolts sampled from west of Ireland to the northern Norwegian Sea over a 25-year period. We also test for changes over time in stomach fullness, diet, condition factor and body length. There was a clear reduction in condition factor for post-smolts sampled in the Norwegian Sea in the period 2003–2012. The post-smolt stomach fullness was also reduced in the same period. The reduction in condition factor is partly explained by reduced stomach fullness, including a reduction of highly energetic fish larvae and Amphipoda in the diet. Feeding on other prey, such as meso-zooplankton and insects, cannot substitute the high-quality fish larvae and Amphipoda in the post-smolt diet. This is the first study to document how salmon post-smolts feeding in the Norwegian Sea are affected by reduced feeding conditions. Possible causes for the observed changes in post-smolt feeding are ocean warming, decreased primary productivity, and reduced recruitment of important fish larvae.

Running on empty? Freshwater feeding by spawning anadromous alewife Alosa pseudoharengus

Anadromous alewife Alosa pseudoharengus (n=202; mean ± s.d. fork length= 231 ± 14 mm) were captured from 10 May to 27 June 2018 in an upper watershed lake on the Isthmus of Chignecto, Canada (45°57'N, 64°14'W). Thirty individuals (mean ± s.d. fork length=250 ± 12 mm) were captured in an adjacent estuary downstream of a tide gate on 25 April 2018. Comparing estuarine to freshwater specimens, mean gonad mass and gonadosomatic indices in males and females decreased approximately 40% and 60%, and 31% and 50%, respectively. Individuals were characterized as pre-spawners in the estuary and spawners in the lake. Males maintained similar body condition throughout the spawning run whereas female condition decreased 9.4% between the estuary and lake. Stomach fullness decreased comparing estuarine and freshwater specimens, yet 93% of stomachs examined from individuals captured in the lake contained prey. Most males fed throughout all spawning stages (3%-17% empty stomachs), while all females fed during pre- and post-spawning stages and some fasted during spawning (11% empty stomachs). Cumulative prey curve never reached an asymptote, either weekly or for the entire sampling period, so freshwater diet may not have been completely described. Calanoid copepods (79.3%IA ) were a diet staple, with the secondary prey of mayfly nymphs (O. Ephemeroptera) consumed more by females (13.6%IA ) than males (6.2%IA ). PERMANOVA and PERMDISP analyses revealed significant dietary differences in freshwater were weekly and not due to dispersion effects, thus most likely due to feeding on various development stages of insect species. Our results challenge the long-held paradigm that anadromous A. pseudoharengus fast during the spawning migration.