Feeding patterns of Lampanyctus pusillus (Pisces: Myctophidae) throughout its ontogenetic development

The trophic ecology of the lanternfish Lampanyctus pusillus was investigated using individuals captured off the Balearic Islands (39°N, 2°E) (western Mediterranean) in December 2009. Based on gut content analyses, the trophic niche breadth, diet composition and selectivity were determined for the entire life cycle of L. pusillus. The larval stages fed actively near the surface during the day, with a feeding incidence (FI) of approximately 71 %. In contrast, the adults fed at night, both in near-surface depths and in the 400 m deep scattering layer, with a higher FI (83 %). Diet analysis revealed a shift in the prey choice throughout ontogenetic development, from preflexion individuals, which selected nauplii and small oncaeids, to postflexion larvae, which consumed a variety of calanoids, mainly Clausocalanus spp., to the adults, which preyed on large organisms, exhibiting positive selectivity for Pleuromamma spp. and euphausiids. These results show that the vertical distribution of larvae and adults is partly conditioned by their respective feeding habits, with larvae feeding on small zooplankton in the upper layer and adults preferring to consume larger taxa that perform nycthemeral migrations.     

Determination of δ13C and δ15N and trophic fractionation in jellyfish: implications for food web ecology

Application of stable isotope analysis (SIA) in jellyfish allows definition of trophic patterns not detectable using gut content analysis alone, but analytical protocols require standardization to avoid bias in interpreting isotopic data. We determined δ¹³C and δ¹⁵N in Aurelia sp. from the northern Gulf of Mexico (30°00′N, 89°00′W–30°24′N, 88°00′W) to define differences in stable isotope composition between body parts and whole body, the effect of lipid extraction on δ¹³C in tissues, and fractionation values from medusa to prey. The isotopic composition of bell and whole Aurelia sp. was not different. The increase in δ¹³C values after lipid removal suggested a correction is needed. To aid future analyses, we derived a correction equation from empirical data for jellyfish samples. Laboratory feeding experiments indicated medusae increased +4 ‰ in δ¹³C and +0.1 ‰ in δ¹⁵N compared to their diet. These results suggest protocols commonly applied for other species may be inaccurate to define Aurelia sp. trophic ecology. Because Aurelia spp. are commonly found in marine ecosystems, accurately defining their trophic role by use of SIA has implications for understanding marine food webs worldwide.     

Feeding opportunities of larval and juvenile cod (Gadus morhua) in a Greenlandic fjord: temporal and spatial linkages between cod and their preferred prey

Feeding of fish depends on a spatial and temporal match with prey, and since larval and juvenile feeding can be highly selective, their preferences for given prey sizes and taxa should be considered when quantifying the actual availability of potential prey. We investigated the diet and prey preferences of the early-life stages of Atlantic cod (Gadus morhua) to quantify the availability of prey during a spring-summer season in a West Greenlandic fjord. We hypothesized that abundances of larval and juvenile cod at size were synchronized to optimal availability of preferred prey in space and time. The present analysis is based on nine cruises each covering 5 stations visited between 24 May and 5 August 2010 comparing zooplankton abundance, cod gut content and distribution patterns. Cod 4–25 mm in length preferred prey of about 5 % of their own length. During ontogeny, their preferences changed from calanoid nauplii towards Pseudocalanus spp. and Calanus spp. copepodites. The larvae/juvenile had an exceptionally high dietary contribution from cladocerans, which were highly preferred by cod larger than 9 mm, while the abundant Metridia longa and the non-calanoid copepods contributed less. These findings stress the importance of focusing on abundance of preferred prey when assessing the actual prey availability to young fish. We found a spatio-temporal overlap between cod and their preferred prey, and observations suggest that advection of both zooplankton and cod contributed to this overlap. Hence, the larval feeding opportunities might be sensitive to climate-related changes affecting the circulation patterns in this fjord.     

Observations on the nocturnal feeding of some mesopelagic decapod crustacea

Feeding in relation to temporal changes in the depth distribution of predator and prey is described for 9 species of mesopelagic decapods from an examination of 268 foreguts. Intensive nighttime feeding appears to be the rule in all species. The smaller decapods Sergestes (Sergestes) atlanticus, Sergestes (Sergestes) sargassi and Sergestes (Sergestes) pectinatus exploit the smaller prey, principally copepods and to a lesser extent ostracods. Larger decapod species Sergestes (Sergestes) henseni, Sergestes (Sergestes) curvatus, Sergestes (Sergia) grandis, Systellaspis debilis, and Acanthephyra purpurea mainly prey on macrozooplankton and micronekton, i.e., chaetognaths, euphausiids, decapods and fish, but copepods also occur in the foreguts. Gennadas valens is exceptional for the high incidence of foraminiferal remains, and a predator-prey relationship seems probable. All 9 decapod species have mixed diets, and pronounced feeding preferences are not evident. However, a high incidence of “secondary” feeding or “dietary contamination” has been deduced from the frequent occurrence of remains of the copepods Pleuromamma spp. and Oncaea spp. in the foreguts of the larger decapod species. Direct feeding cannot have occurred, since the depth distributions of these copepods and decapods are disjunct by day and night. It is concluded that the remains of Pleuromamma probably represent the food of the larger prey such as chaetognaths etc. which are eaten by the decapods. The presence of Oncaea is speculatively attributed to a possible ectoparasitic relationship with the larger prey items, but confirmatory evidence is required. These anomalies suggest that caution must be exercised in deducing predator-prey relationships simply from gut contents without consideration of distributional factors.     

Ontogenetic shift in foraging habit of ocean sunfish Mola mola from dietary and behavioral studies

The ocean sunfish (Mola mola) is typically considered to feed on gelatinous zooplankton, but reports in the literature describe various benthic organisms being found in their stomachs. This might reflect ontogenetic dietary shift, as little was known about the foraging habit of this species. We examined their foraging habits using dietary analyses in combination with a behavioral study in Iwate, Japan (39°22′N, 141°58′E) from 2009 to 2010. Our stomach content analyses (n = 17, 31–250 cm total length) suggested that small sunfish (<50 cm) feed on benthic crustaceans, but large sunfish (>200 cm) feed on jellyfish. Larger sunfish showed higher values of both carbon and nitrogen stable isotope ratios. Deployment of accelerometers and animal-borne cameras on small sunfish in July (49–58 cm, n = 5) suggested their possibility of feeding, while they stayed near the seabed. This indicates that small sunfish might feed on benthic preys. Deployment of accelero-magnetometers on large sunfish in July (84–164 cm, n = 4) clarified that the large sunfish in July swam back and forth between the surface and deep water (>100 m). Temporary decelerations, which were considered to be associated with feeding of planktonic prey, were observed in deep water. Whereas deployment of accelero-magnetometers on large sunfish in November (105 cm, n = 3) showed several bursts, they swam within the mixed layer (0–100 m), which might be associated with chasing of rapid prey. These results suggest that ocean sunfish have heterogeneous diets depending on their body size and possibly season.     

Feeding ecology of the green turtle (Chelonia mydas) at rocky reefs in western South Atlantic

Feeding ecology of green turtles was investigated between January 2005 and April 2008 at Arvoredo Reserve, Brazil (27°17′S, 48°18′W). Data were obtained through the performance of observational sessions, geo-referenced counts, benthic surveys, capture and recapture of individuals, and oesophageal lavages. This protected area was identified as an important green turtle feeding ground, used year-round by juveniles (curved carapace length = 32–83 cm). Turtles fed close to the rocky shores of the area and selected grazing sites commonly at hard-to-reach, near-vertical portions of the rocks. They were less active in cold months, and more abundant at shallow areas of the reef (0–5 m), where their preferred food items occurred. Their diet was dominated by macroalgae species but invertebrates were also present. Their main food item was the red algae Pterocladiella capillacea, which seems to be eaten through periodical cropping of its tips. Observational methods such as the ones applied here could be incorporated to other research programs aiming to understand the relationships between Chelonia mydas feeding populations and their environment.     

Combined effect of temperature and food concentration on the grazing rate of the rotifer Brachionus plicatilis

We developed a predictive relationship to determine the grazing rate of Brachionus plicatilis at given temperatures and food concentrations; this function could be applied to experimental culturing and aquaculture practices. Grazing experiments were conducted at temperatures between 5°C and 40°C and at food concentrations, of the flagellate Isochrysis galbana, ranging between ~0 and 10⁶ ml^-1. In total, 136 grazing rates were determined, using the prey depletion method, for rotifers acclimated to treatments for 0.5 or 4 h. The response of grazing rate to temperature and food concentration was described using a model that combined a rectangular hyperbolic function for food concentration and a sigmoidal function for temperature. Using non-linear curve-fitting methods an equation was obtained: G=(452F)/(159000+F)Ǵ.94/(1+2190002T^-4.35) , where G is the grazing rate (flagellates rotifer^-1 min^-1), F is the food concentration (flagellates ml^-1), and T is temperature (°C). The equation indicates a maximum grazing rate of ~35 prey rotifer^-1 min^-1, above ~4᎒⁵ prey ml^-1 and 25°C.     

Brooded coral larvae differ in their response to high temperature and elevated pCO2 depending on the day of release

To evaluate the effects of temperature and pCO₂ on coral larvae, brooded larvae of Pocillopora damicornis from Nanwan Bay, Taiwan (21°56.179′N, 120°44.85′E), were exposed to ambient (419–470 μatm) and high (604–742 μatm) pCO₂ at ~25 and ~29 °C in two experiments conducted in March 2010 and March 2012. Larvae were sampled from four consecutive lunar days (LD) synchronized with spawning following the new moon, incubated in treatments for 24 h, and measured for respiration, maximum photochemical efficiency of PSII (F _v/F _m), and mortality. The most striking outcome was a strong effect of time (i.e., LD) on larvae performance: respiration was affected by an LD × temperature interaction in 2010 and 2012, as well as an LD × pCO₂ × temperature interaction in 2012; F _v/F _m was affected by LD in 2010 (but not 2012); and mortality was affected by an LD × pCO₂ interaction in 2010, and an LD × temperature interaction in 2012. There were no main effects of pCO₂ in 2010, but in 2012, high pCO₂ depressed metabolic rate and reduced mortality. Therefore, differences in larval performance depended on day of release and resulted in varying susceptibility to future predicted environmental conditions. These results underscore the importance of considering larval brood variation across days when designing experiments. Subtle differences in experimental outcomes between years suggest that transgenerational plasticity in combination with unique histories of exposure to physical conditions can modulate the response of brooded coral larvae to climate change and ocean acidification.     

A jellyfish diet for the herbivorous green turtle Chelonia mydas in the temperate SW Atlantic

Feeding ecology of juvenile green turtles (Chelonia mydas) was studied from 2008 to 2011 at Samborombón Bay (35°30′–36°30′S, Argentina), combining data on digestive tract examination and stable isotope analysis through a Bayesian mixing model. We found that animal matter, in particular gelatinous plankton, was consumed in large proportions compared to herbivorous food items such as terrestrial plants and macroalgae. This diet is facilitated by the high abundance of gelatinous plankton in the region, thus confirming the adaptive foraging behaviour of the juveniles according to prey abundance in the SW Atlantic. To our knowledge, this is the first study to employ this combination of techniques and to conclusively demonstrate that animal matter, in particular gelatinous plankton, is important in the diet of the neritic green sea turtles.     

Energy demand of larval and juvenile Cape horse mackerels, Trachurus capensis, and indications of hypoxia tolerance as benefit in a changing environment

Trachurus capensis is an important fisheries resource in the degraded Namibian upwelling ecosystem. Food supply and shoaling of hypoxic zones are hypothesised to influence the species’ recruitment success. This paper is the first to quantify energy requirements and hypoxia tolerance of larval and juvenile stages of a Trachurus species. We measured normoxic respiration rates of T. capensis with a size range from 0.001 to 20.8 g wet mass (WM) collected off Cape Town (33.9°S, 18.5°E, 12/2009) and in the northern Benguela (17–24°S, 11–15°E, 02/2011). Routine metabolic rate (RMR) and standard routine rate (SRR) (mg O₂ h^?1) followed the allometric functions RMR = 0.418 WM^0.774 and SRR = 0.275 WM^0.855, respectively. Larvae and juveniles had comparatively high metabolic rates, and the energy demand of juveniles at the upper end of the size range appeared too high to be fuelled by a copepod diet alone. T. capensis’ early life stages showed a high tolerance to hypoxic conditions. RMR in larvae did not change until 30 % O₂sat at 18 °C. In juveniles, critical oxygen saturation levels were low (P_C for SRR = 11.2 ± 1.7 % O₂sat and P_C for RMR = 13.2 ± 1.6 % O₂sat at 20 °C) and oxy-regulation effective (regulation index = 0.78 ± 0.09). A high hypoxia tolerance may facilitate the retention of larvae in near-shore waters providing favourable feeding conditions and allowing juveniles to exploit food resources in the oxygen minimum zone. These mechanisms seem to well adapt T. capensis to a habitat affected by spreading hypoxic zones and probably enhance its recruitment success.     

Contrast in the importance of arrow squid as prey of male New Zealand sea lions and New Zealand fur seals at The Snares,subantarctic New Zealand

New Zealand sea lions (Phocarctos hookeri) are threatened by incidental bycatch in the trawl fishery for southern arrow squid (Nototodarus sloanii). An overlap between the fishery and foraging sea lions has previously been interpreted as one piece of evidence supporting resource competition for squid. However, there is currently no consensus about the importance of squid in the diet of New Zealand sea lions. Therefore, we investigated this importance independently of spatial and temporal differences in squid availability through a simultaneous study with sympatric New Zealand fur seals (Arctocephalus forsteri), a species known to target arrow squid. Diet sampling at The Snares (48°01′S 166°32′E), subantarctic New Zealand, in February 2012 coincided with peak annual catch in the nearby squid fishery. Diets were deduced by analyses of diagnostic prey remains from scats (faeces) and casts (regurgitations). The contribution of each prey species to the diet was quantified using the per cent index of relative importance (% IRI) that combined frequency of occurrence, mass and number of prey items. Arrow squid was a minor component in sea lion scats (2 % IRI), and none was found in their casts. In contrast, arrow squid was the major component in fur seal scats and casts (93 and 99 % IRI, respectively). This study found that New Zealand sea lions ate minimal squid at a time when squid was clearly available as evidenced by the diet of New Zealand fur seals; hence, there was no indication of resource competition between sea lions and the squid fishery.     

Temporal changes in the trophic ecology of the asymbiotic gorgonian Leptogorgia virgulata

Gorgonians are widespread sub-littoral benthic suspension feeders in the world oceans. However, data on their trophic ecology and role in benthic–pelagic coupling and biogeochemical cycles remain limited. This study assesses the trophic ecology of Leptogorgia virgulata in the Skidaway River estuary, USA (31.9896N, 81.0242W) by analysing carbon and nitrogen isotopic signatures of its soft tissue and different-sized fractions of particulate organic matter (POM) in its environment. Samples were taken in 5 April, 2 August, and 15 October 2012 and 11 January 2013. Results support a distinct temporal shift in the diet of L. virgulata from the POM fraction <10 µm (i.e. pico- and nanoplankton) to the 10–63-µm fraction (i.e. microplankton). This trophic regime is likely associated with the natural abundance of prey items within these size classes, thus suggesting that L. virgulata may be an opportunistic feeder, and seasonal shifts in food availability in the water column affect its diet. As such small prey items affect the bioenergetics of L. virgulata, it is important to understand the implications of changes in food availability associated with environmental drivers on the physiology and population dynamics of this dominant species in the western Atlantic Ocean.     

Trophic role of small cyclopoid copepod nauplii in the microbial food web: a case study in the coastal upwelling system off central Chile

Copepod grazing impact on planktonic communities has commonly been underestimated due to the lack of information on naupliar feeding behaviour and ingestion rates. That is particularly true for small cyclopoid copepods, whose nauplii are mainly in the microzooplankton size range (<200 μm). The trophic role of Oithona spp. nauplii was investigated off Concepción (central Chile, ~36°S) during the highly productive upwelling season, when maximum abundances of these nauplii were expected. Diet composition, ingestion rates, and food-type preferences were assessed through grazing experiments with different size fractions of natural planktonic assemblages (<3, <20, <100, and <125 μm) and cultures of the nanoflagellate Isochrysis galbana. When the Oithona spp. nauplii were offered a wide range of size fractions as food (pico- to microplankton), they mostly ingested small (2–5 μm) nanoflagellates (5–63 × 10³ cells nauplius⁻¹ day⁻¹). No ingestion on microplankton was detected, and picoplankton was mainly ingested when it was the only food available. Daily carbon (C) uptake by the nauplii ranged between 28 and 775 ng C nauplius⁻¹, representing an overall mean of 378% of their body C. Our relatively high ingestion rate estimates can be explained by methodological constraints in previous studies on naupliar feeding, including those dealing with “over-crowding” and “edge” effects. Overall, the grazing impact of the Oithona spp. nauplii on the prey C standing stocks amounts up to 21% (average = 13%) for picoplankton and 54% (average = 28%) for nanoplankton. These estimates imply that the nauplii of the most dominant cyclopoid copepods exert a significant control on the abundances of nanoplankton assemblages and, thereby, represent an important trophic link between the classical and microbial food webs in this coastal upwelling system.     

Parthenogenetic reproduction of Diaphanosoma celebensis (Crustacea: Cladocera). Effect of algae and algal density on survival, growth, life span and neonate production

The cladoceran Diaphanosoma celebensis Stingelin is reported on for the first time from Indian waters (Mandovi estuary, Goa). Amictic females were maintained in the laboratory (temperature 24 ± 1 °C and salinity 17 psu) for three successive generations in order to follow the parthenogenetic reproductive behaviour, growth, survival and neonate production. The mean life span and body length of adult females in the three generations showed some variations and ranged from 9 to 12.5 d and 842 to 932 μm, respectively. The mean length of the neonates produced also varied (283 to 446 μm) in the three generations. Cladoceran preference for three phytoplankton food sources, i.e. Isochrysis galbana (Parke), Chaetoceros calcitrans (Paulsen) and Tetraselmis gracilis (Kylin), was determined. Growth was faster in the initial stage with all three diets but slowed down in later life. Increased food concentrations resulted in higher neonate production but reduced the life span of females. However, long-term feeding experiments revealed that the percentage survival was high with I. galbana and low with C. calcitrans. Received: 23 June 1999 / Accepted: 20 September 1999     

Elevated pCO2 causes developmental delay in early larval Pacific oysters, Crassostrea gigas

Increasing atmospheric CO₂ equilibrates with surface seawater, elevating the concentration of aqueous hydrogen ions. This process, ocean acidification, is a future and contemporary concern for aquatic organisms, causing failures in Pacific oyster (Crassostrea gigas) aquaculture. This experiment determines the effect of elevated pCO₂ on the early development of C. gigas larvae from a wild Pacific Northwest population. Adults were collected from Friday Harbor, Washington, USA (48°31.7′N, 12°1.1′W) and spawned in July 2011. Larvae were exposed to Ambient (400 μatm CO₂), MidCO₂ (700 μatm), or HighCO₂ (1,000 μatm). After 24 h, a greater proportion of larvae in the HighCO₂ treatment were calcified as compared to Ambient. This unexpected observation is attributed to increased metabolic rate coupled with sufficient energy resources. Oyster larvae raised at HighCO₂ showed evidence of a developmental delay by 3 days post-fertilization, which resulted in smaller larvae that were less calcified.     

Responses of echinoid larvae to food patches of different algal densities

High densities of larvae have been found in areas of high primary production, but it remains unclear whether this is the result of hydrodynamics or of larval aggregative behaviour in the presence of food. In this study, we examined changes in the vertical distribution and swimming patterns of four-armed larvae of the sea-urchin Echinometra lucunter (Linnaeus) around food patches of a range of microalgal densities. We reared larvae in the laboratory in a high or low concentration of either single (Isochrysis galbana) or mixed (I. galbana, Dunaliella tertiolecta, Thalassiosira weissflogii) microalgal species. In Plexiglas cylinders, we experimentally constructed haloclines in which the salinity of the bottom water-layer was 33‰ and that of the top water-layer was 24‰. In a thin layer in the middle of the halocline, we inserted a food patch that consisted of 0, 2500, 5000 or 10 000 T. weissflogii cells ml⁻¹. The presence of a food patch had a pronounced effect on the vertical distribution of larvae. This effect depended upon the algal density of the food patch and varied with dietary conditioning. The number of larvae that were above or within the patch decreased with increasing algal density, and was greater if larvae were reared in low-ration or single-species diets than in high-ration or mixed-species diets. Tracking of individual vertical swimming paths showed that within a few minutes, larvae swam into the patches of low algal density, and to positions just below the patches of the two higher algal densities, and remained there until the end of the experimental period. The greater number of algal cells in the digestive tracts of larvae from treatments with a food patch than in those without a patch confirmed that larvae were feeding on the microalgal cells of the patch. To our knowledge, this is the first study to experimentally show an aggregative behavioural response of invertebrate larvae to a food patch. Such a response may reduce the probability of food limitation and therefore enhance larval survival. Received: 14 February 1997 / Accepted: 24 September 1997     

Food and feeding dynamics of the larval Antarctic fishNototheniops larseni

The feeding dynamics of larvae of the Antarctic fishNototheniops larseni were analyzed from data collected over three years in Bransfield Strait and adjacent waters (Antarctica). Seasonal feeding was examined from 1977/1978 (November–March). The diel feeding cycle was investigated during a 96 h station established in February 1976, while food selection was analyzed using larvae and zooplankton samples collected in February 1982. Hatching occurs in early spring, and larvae fed on eggs of calanoid copepods and on cyclopoid copepods. Copepod eggs were the principal food near the pack ice, and cyclopoids in open waters. Cyclopoids were the staple food in summer. Eggs of the Antarctic krillEuphausia superba were ingested selectively and formed major portions of the larval summer diet in neritic (Joinville Island) and oceanic (Elephant Island) spawning areas ofE. superba. In the fall, copepods predominated in the diets. Most abundant and most frequently ingested prey in summer and fall wereOncaea spp. Feeding commenced at dawn and continued at least until dusk. Krill eggs were taken chiefly during morning hours and egg incidence declined during the day, suggesting that eggs were ingested soon after spawning. Prey size at the onset of feeding was estimated as 0.130 to 0.330 mm. Size-selective feeding was evident in small larvae, while in larger larvae median prey length remained constant. High feeding incidence among yolk-sac larvae in spring, high overall feeding incidence in summer, and size-selective foraging of small larvae suggested favorable feeding conditions in the 1977/1978 season. Yolk-absorption times in Antarctic fish larvae vary on a scale of weeks and may be further retarded due to early feeding. Hence, year-to-year variability of yolk incidence inN. larseni indicated variable biotic environments of early feeding larvae rather than temporal shifts of hatching periods. As hatching periods are constant between years in contrast to the variable retreat of the pack ice and subsequent onset of the production cycle in space and time, maternal yolk reserves are probably utilized to compensate for such variations.     

Chemical composition of dietary species of marine unicellular algae and rotifers with emphasis on fatty acids

The lipid profiles of a few species of marine unicellular algae and yeast were studied with emphasis on fatty acids as part of a search for the nutritional value of plankton to the diet of marine fish larvae commonly used in marine hatcheries. The general proximate chemistry of rotifers was closely related to the proximate chemistry of the diet organism, exhibiting a higher content of protein and carbohydrate and a lower content of lipid. Major lipids in all algae, yeast and rotifers comprised mono-, di- and tri-glycerides and polar lipids. The algae Chaetoceros gracilis Schutt, Isochrysis galbana Parke and their respective algaefed rotifers exhibited higher amounts of neutral lipids, consisting mainly of cyclic and branched polyunsaturated components. Fatty acid composition of the algae was species-specific, with the highest ratio of polyethylenic to saturated and monoethylenic acid in I. galbana and Phaeodactylum tricornutum Bohlin, and the highest content (15%) of n-3 highly unsaturated fatty acids in Nannochloropsis salina and P. tricornutum. A closely mirrored distribution of the fatty acids, but with a lower amount of n-3 highly unsaturated fatty acids, was present in the respective algae-fed rotifers. Comparison of the fatty acid spectrum of Artemia sp. and Euterpina acutifrons grown in the laboratory on I. galbana with zooplankton samples of E. acutifrons and Oitona nana collected from the sea showed a higher concentration of docosahexaenoic acid (22:6 n-3) in the naturally collected sample. The results indicate that the efficacy of the food algae C. gracilis and I. galbana in increasing the survival of fish larvae in marine hatcheries is not obvious on the sole basis of fatty acid composition.     

Does the antidiabetic drug metformin affect embryo development and the health of brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> f. <Emphasis Type="Italic">fario</Emphasis>)?

Background

Due to the rising number of type 2 diabetes patients, the antidiabetic drug, metformin is currently among those pharmaceuticals with the highest consumption rates worldwide. Via sewage-treatment plants, metformin enters surface waters where it is frequently detected in low concentrations (µg/L). Since possible adverse effects of this substance in aquatic organisms have been insufficiently explored to date, the aim of this study was to investigate the impact of metformin on health and development in brown trout (Salmo trutta f. fario) and its microbiome.

Results

Brown trout embryos were exposed to 0, 1, 10, 100 and 1000 µg/L metformin over a period from 48 days post fertilisation (dpf) until 8 weeks post-yolk sac consumption at 7 °C (156 dpf) and 11 °C (143 dpf). Chemical analyses in tissues of exposed fish showed the concentration-dependent presence of metformin in the larvae. Mortality, embryonic development, body length, liver tissue integrity, stress protein levels and swimming behaviour were not influenced. However, compared to the controls, the amount of hepatic glycogen was higher in larvae exposed to metformin, especially in fish exposed to the lowest metformin concentration of 1 µg/L, which is environmentally relevant. At higher metformin concentrations, the glycogen content in the liver showed a high variability, especially for larvae exposed to 1000 µg/L metformin. Furthermore, the body weight of fish exposed to 10 and 100 µg/L metformin at 7 °C and to 1 µg/L metformin at 11 °C was decreased compared with the respective controls. The results of the microbiome analyses indicated a shift in the bacteria distribution in fish exposed to 1 and 10 µg/L metformin at 7 °C and to 100 µg/L metformin at 11 °C, leading to an increase of Proteobacteria and a reduction of Firmicutes and Actinobacteria.

Conclusions

Overall, weight reduction and the increased glycogen content belong to the described pharmaceutical effects of the drug in humans, but this study showed that they also occur in brown trout larvae. The impact of a shift in the intestinal microbiome caused by metformin on the immune system and vitality of the host organism should be the subject of further research before assessing the environmental relevance of the pharmaceutical.

     

Particle retention and selection by larvae and spat of Ostrea edulis in algal suspensions

Grazing rates and electivity indices of larvae and spat of Ostrea edulis L. were, measured and examined in relation to certain physical parameters using a flow-through system. Retention and size-selection were determined for the major particle sizes present in cultures of Isochrysis galbana Parke, an alga used frequently as food for bivalves. Cultures of the algae Dunaliella tertiolecta Butcher and Phaeodactylum tricornutum Bohlin were used as sources of particle suspensions of various sizes and shapes, respectively. While increases in flow rate caused increased grazing, the mode of selection of I. galbana particles remained constant. Filtration rate, F _f was related to body size, W, by the general allometric equation R _f =aW ^b,while particle-size preference in suspensions of I. galbana by both larvae and spat of O. edulis was independent of W. Grazing rates increased with temperature to an optimum temperature, which was related to the acclimation temperature. Increases above this optimum caused a reduction in feeding activity. No significant change in particle size-preference in the I. galbana suspension with temperature was observed. Grazing rates and selection were dependent, however, on particle number and volume. Both larvae and spat displayed maximum retention at optimum particle concentrations which tended to decrease with increasing particle size. Variations in cell shape of P. tricornutum had no measurable effect on selectivity by O. edulis.