Veligers of the invasive bivalve Limnoperna fortunei in the diet of indigenous fish larvae in a eutrophic subtropical reservoir

Larval fish development depends largely on their ability to capture and ingest food items, and on food availability. In this context, invasive species, eutrophication and river impoundments have complex impacts on fish larvae. Using samples collected in 2005–2009 in the Salto Grande reservoir (Argentina–Uruguay), periodically affected by cyanobacterial blooms, we studied the impact of the larvae of the exotic bivalve Limnoperna fortunei (Dunker, 1857) (Bivalvia) on larval fish diets. Compared with other nearby waterbodies, the abundance of fish larvae was scarcer in the reservoir, especially during algal bloom periods. Only 20% of the larval fish with gut contents fed on L. fortunei veligers. Seven fish taxa (of a total of 12) consumed veligers of L. fortunei, but only two showed a preference for this prey. Taxonomic changes in the larval fish assemblages due to the river's impoundment, and temporal uncoupling between veliger densities (affected by the toxigenic effects of Microcystis spp.) and ichthyoplankton could account for the comparatively low trophic importance of the invasive bivalve's veligers. These results reflect the complexity of interactions brought about when the same invasive species invades different environments, underscoring that the impacts involved depend as much on the invader, as on the regional and ecological settings of the area invaded.     

Prey selection by larvae of Prochilodus lineatus (Pisces: Curimatidae): indigenous zooplankton versus veligers of the introduced bivalve Limnoperna fortunei (Bivalvia: Mitilidae)

We studied experimentally the feeding selectivity of larvae of Prochilodus lineatus (Pisces), with particular emphasis on the role of veligers of the exotic bivalve Limnoperna fortunei. Three concentrations of veligers were offered to three developmental stages of P. lineatus. Veliger concentrations were: (1) higher than in the field (“enriched”, 0.09 ind. ml⁻¹), (2) unmodified from field conditions (“normal”, 0.06 ind. ml⁻¹), and (3) lower than in the field (“low”, 0.02 ind. ml⁻¹). Fish developmental stages were protolarvae (approx. 10 days old), mesolarvae (17 days), and metalarvae (25 days). Proportions (in terms of numbers and biomass) and selectivity values were calculated for each prey item evaluated: veligers, small cladocerans + nauplii, medium-sized cladocerans, copepodits, and large cladocerans + copepods. Protolarvae and mesolarvae consumed veligers almost exclusively (88–90%, both in numbers and in biomass) when offered prey enriched in veligers, whereas for metalarvae veligers represented only 16.0% of the food consumed. At lower veliger concentrations, only protolarvae preferred Limnoperna veligers, whereas older fishes switched gradually to crustacean plankton. We conclude that veligers are preferred by the early fish developmental stages, and we speculate that this may be because their slower swimming makes them easier to capture than planktonic crustaceans. However, as fish larvae grow larger, veligers become too small a prey for their energetic needs, and they switch to larger items like cladocerans and copepods. We anticipate that this new and abundant food resource has an important impact on the survival and growth of P. lineatus.     

Larvae of the invasive species <Emphasis Type="Italic">Limnoperna fortunei</Emphasis> (Bivalvia) in the diet of fish larvae in the Paraná River,Argentina

To assess the trophic impact of the planktonic larvae of the invasive Asian bivalve Limnoperna fortunei, introduced in South America around 1990, we investigated the gut contents of fish larvae collected at monthly intervals between October 2000 and March 2001 at three locations along a 600 km stretch of the Paraná River, and during November 2004 in two areas of marginal lagoons connected to the river near the city of San Nicolás, Argentina. Zooplankton was also collected in the lagoons in 2004. In total, 11,956 fish larvae were retrieved, of which 1,511 were used for detailed analyses. Of the 15 fish taxa collected, 11 had veligers of L. fortunei in their gut. Fish larvae with empty guts represented 60% (San Nicolás) to 72% (Paraná River) of the total number of fish. Proportions of feeding fish larvae with L. fortunei veligers in their guts varied between 20% (San Nicolás) and 56% (Paraná River); in 15% of the guts analyzed, L. fortunei was the only food item recorded. For those specimens that had consumed L. fortunei larvae and any other food item, L. fortunei was the most important item in 55% (Paraná River) to 71% (San Nicolás) of the animals in terms of biomass. No major temporal or spatial changes in the diet were observed along the Paraná River, but the relative biomass contribution of L. fortunei larvae differed strongly in fishes of different developmental stage. In protolarvae and mesolarvae, veligers accounted for 30–35% of the gut contents. In metalarvae, veligers accounted for only 3%, indicating enhanced food supply for the earliest fish life stages. Comparison of the relative proportions of the three main zooplankton types (L. fortunei veligers, cladocerans, and copepods) in the water and in larval fish guts indicates that L. fortunei is always selected positively over the other two prey types. While our results strongly suggest that the expansion of L. fortunei results in an enhanced food supply for local fish populations, they do not necessarily imply that the overall effect on the ecosystem in general, and on the fish fauna in particular is beneficial.     

Growth response of African catfish,Clarias gariepinus (B.), larvae and fingerlings fed protease‐incorporated diets

African catfish, Clarias gariepinus (B.), is one of the promising freshwater fish species in African aquaculture but the expansion of its farming needs more production of its larvae. The use of live food organisms at first feeding for larvae is still obligatory. That increases the cost of larvae production. Hence, the incorporating of exogenous enzymes especially protease in artificial microdiets may provide affordable alternatives for enhancing the larvae performance. The present study was carried out to evaluate the growth and survival of larvae or fingerlings of African catfish fed artificial diets incorporated with different protease levels. Four artificial diets were formulated and enriched with protease enzyme at levels of 0.0, 750, 1,000, and 1,250 unit/kg diet; after that diets were made into crumbles (100–200 µm diameter). After absorption of the yolk sac, diets were offered to fish larvae (3.6 ± 0.2 mg) in triplicates as a starter feed up to apparent satiation every two hours for 30 days. In another treatment, fish larvae were fed on newly hatched Artemia nauplii (2,500 Artemia/L) as a starter food. In another experiment, African catfish fingerlings (10.1 ± 1.6 g) were fed on the same diets up to satiation twice a day for 2 months. It was noticed that the dietary protease improved larval growth and survival but not as Artemia nauplii did where fish larvae fed on Artemia nauplii showed highest growth and survival followed by those fed a diet enriched with 1,250 unit/kg diet of protease. The mortality of larvae fed protease‐enriched diets as well as the control diet was occurred mostly at the first week reaching its maximum at the third week. The poor growth was observed with fish larvae fed the control diet. Meanwhile, catfish fingerlings fed protease‐enriched diets showed higher growth over those fed the control diet. The larvae survival (11.0%–41.7%) was enhanced by increasing protease levels and it was lower than that of fingerlings (95.6%–100.0%). Furthermore, protein retention and digestibility were significantly improved with protease supplementation over the control diet especially at a level of 1,000 unit/kg diet. As compared with the previous studies, live food should be used in larvae rearing for the first week after that a starter diet enriched with protease at levels of 1,250 unit/kg diet should be used. In case of fish fingerlings, the dry diets should be enriched with 1,100 unit/kg diet to improve diet digestibility and subsequently enhance their growth.     

Veligers from the nudibranch <Emphasis Type="Italic">Dendronotus</Emphasis><Emphasis Type="Italic">frondosus</Emphasis> show shell growth and extended planktonic period in laboratory culture

The planktonic period of planktotrophic veliger larvae from the nudibranch Dendronotus frondosus was characterized by laboratory culture methods. Larvae in culture successfully metamorphosed at 73–86 days after hatching. These veligers have Type 2 (Thompson) larval shells that significantly increased in length over the first 7–14 days after hatching. Direct observations of the development of nudibranch larvae with Type 2 protoconchs are limited, and these data help clarify previous attempts to correlate shell type and growth with minimum planktonic periods. Although these are not absolute values for the planktonic period of D. frondosus larvae, these data show the potential for extended larval dispersal and may help explain reports of an extensive geographic range in north-temperate waters for this species.     

Suitability of monotypic and mixed diets for Anopheles hermsi larval development

The developmental time and survival to eclosion of Anopheles hermsi Barr & Guptavanij fed monotypic and mixed diets of ten food types were examined in laboratory studies. Larvae fed monotypic diets containing animal detritus (freeze‐dried rotifers, freeze‐dried Daphnia pulicaria, and TetraMin® fish food flakes) and the mixotrophic protistan Cryptomonas ovata developed faster and survived better than larvae that were fed other monotypic diets. Survival to adulthood of larvae fed several concentrations of the diatom Planothidium (=Achnanthes) lanceolatum was poor (<13%) and larval development time was approximately twice that of larvae fed TetraMin® fish food flakes, the standard laboratory diet. Larvae fed monotypic diets containing prokaryotes (bacteria [Bacillus cereus] and cyanobacteria [Oscillatoria prolifera]) and brewer's yeast (Saccharomyces cerevisiae) failed to survive beyond the 1^st and 2^nd instar, respectively. Larvae fed only chlorophytes, single‐celled Chlamydomonas reinhardtii and filamentous Spirogyra communis, failed to complete larval development, regardless of the concentration tested. Cohorts fed a combination of food types (mixed diets) usually developed better than cohorts fed monotypic diets. Food types that failed to support complete development when fed alone often facilitated development to adulthood when fed in combination with food types containing >1% C₂₀ polyunsaturated fatty acids as total fat, but regardless of essential fatty acid content, algae that produced mucilage and filaments that sank out of the feeding zone were poor quality diets.     

Effects of live food and formulated diets on survival, growth and protein content of first-feeding larvae of Plelteobagrus fulvidraco

In recent years, much progress has been made in the rearing of fish larvae fed only artificial diets. A preliminary study was made in an attempt to evaluate the effects of live food and formulated diets on survival, growth and body protein content of first‐feeding larvae of Plelteobagrus fulvidraco. Three test diets varying in protein level were formulated: Feed 1 containing 45% protein, Feed 2 with 50% protein and Feed 3 with 55% protein. Larvae fed live food (newly hatched Artemia, unenriched) were the control. The experiment started 3 days post‐hatch and lasted for 23 days. At the end of the 23‐day trial, survival was best in the control group (65.6%) whereby the final body weight and specific growth rate (SGR) were significantly lower than those in the test feed groups. At the same time, coefficients of variation for SGR and final body weight in the test groups were significantly higher than those in the control. Whole body protein content in all treatments showed a similar tendency during development: significantly higher 3 days post‐hatch, then decreasing significantly, and then increasing unstatistically 10 days post‐hatch. All results suggest that live food is still better for first‐feeding larvae of P. fulvidraco, since live food leads to healthier larvae growth.     

The importance of zooplankton in the diets of three native fish species in floodplain waterholes of a dryland river,the Macintyre River,Australia

The zooplankton of freshwater systems has been recognized as an important energy resource for fish of small body size that, in turn, provide energy to piscivorous fish consumers higher up the food web. This study evaluates the importance of zooplankton to the diets of three species of fish living in floodplain waterholes of an Australian dryland river. The species selected for study represent different trophic categories in waterhole food webs: Ambassis agassizii is a microcarnivore, Leiopotherapon unicolor is an omnivore, and Nematalosa erebi is a detritivore. Dietary differences among size classes of each species were also evaluated to understand possible ontogenetic shifts in zooplankton consumption. Ambassis agassizii fed primarily on zooplankton (99.9%, made up mostly of 81.6% Calanoida and 17.4% Moinidae), regardless of the size of individual fish. Leiopotherapon unicolor fed on zooplankton (47%, mostly Daphniidae and Moinidae) and aquatic insects (46.7%). Smaller individuals of Leiopotherapon unicolor (30–49 mm TL—total length) were responsible for 36.1% of the plankton consumed by the species. Nematalosa erebi fed on detritus (84.6%) with zooplankton (Calanoida, Moinidae, and Cyclopoida) contributing only 13.7% of the mean diet. Smaller individuals (40–69 mm TL) were responsible for 98% of the plankton consumed by Nematalosa erebi, and individuals of 40–49 mm (TL) fed exclusively on zooplankton (53.8% Moinidae and 46.2% Calanoida). Although the three fish species had different diets, reflecting differences in species-specific and ontogenetic morphological and behavioral characteristics, zooplankton formed the basis of the diet of all species when young. These results confirm the importance of zooplankton as a major food resource for three fish species and smaller size classes of these species in floodplain waterholes of the Macintyre River, Australia. Guest editors: U. M. Azeiteiro, I. Jenkinson & M. J. Pereira Plankton Studies     

Fatty acid alterations in the detritivorous Prochilodus lineatus promoted by opportunistic feeding on sewage discharges in the Río de la Plata estuary

Muscle fatty acid profiles and PCB contents of the detritivorous species Prochilodus lineatus and its diet (stomach contents, settling particles and sediments) were analysed from reference and polluted areas of the Paraná‐Rio de la Plata basin, to evaluate the alterations produced by opportunistic feeding on sewage discharges. Overall muscle fatty acid composition was dominated by saturated and monounsaturated 16 and 18 carbon (18 C‐FA) components with reduced long‐chain polyunsaturated fatty acids (LC‐PUFA). Compared to sediments, settling particles and stomach contents were enriched in lipids and had a similar fatty acid composition. Opportunistic feeding on sewage detritus at Buenos Aires resulted in enhanced PCB and triglyceride accumulation, with higher proportions of 18 C‐FA and lower proportions of 16:1 and LC‐PUFA compared to fish from northern pristine reaches of the basin. Mid‐Paraná showed intermediate values reflecting mixing of the North stock with migrating Buenos Aires P. lineatus identified by their lipid and contaminant profile. According to multivariate analyses, this geographical variation of fatty acid composition was strongly influenced by PCB concentration. Prochilodus lineatus assimilates the energy subsidy of sewage inputs through enhanced lipogenesis with dominant 18 C‐FA and significant amounts of valuable LC‐PUFA. This lipid alteration facilitates the bioaccumulation of PCBs which in turn may reinforce the adipogenic effect of sewage feeding.     

Effect of varying dietary levels of ω6 polyunsaturated fatty acids during the early ontogeny of the sea scallop, Placopecten magellanicus

This study investigated the effects of selected microalgal diets on growth, survival and fatty acid composition of sea scallops, Placopecten magellanicus, from egg hatching to postlarvae. Scallops were offered Pavlova lutheri (MONO) and Pavlova sp. (strain CCMP 459, P459) in combination with Chaetoceros muelleri (CHGRA) and P459 alone. These diets exhibited varying proportions of ω6 docosapentaenoic acid (22:5ω6, DPA) which represented 8.9% of total fatty acids in P459 compared to 5.4% in P459-CHGRA and only 0.5% in MONO-CHGRA. For experiment I, larvae were fed three diets (MONO-CHGRA, P459-CHGRA or P459 alone) for 35 days after fertilization. For experiment II, larvae were fed P459-CHGRA for 21 days and split among the three diets until 39 days post-fertilization. For experiment III, 4-day-old larvae were exposed to P459-CHGRA until they become postlarvae. MONO-CHGRA failed to produce pediveligers when fed to early veligers but yielded competent larvae when fed to late veligers. This may be related to the low ω6 DPA content of this diet. High accumulation of DPA by early veligers suggests a nutritional requirement for this fatty acid. Unialgal P459 supported lower pediveliger production and lower growth rate than other diets containing CHGRA. This may be the effect of higher levels of energetic substrates in CHGRA-containing diets. Finally, P459-CHGRA yielded the best survival and growth rate during the whole larval period. All three experiments showed marked arachidonic acid (20:4ω6, AA) accumulation in early veligers (4 to 21 days) and in pediveligers (32 to 43 days). Accumulation of AA during metamorphosis might reflect stimulation of immune functions due to pathogen infection and degradation of larval organs or the role of AA in cell signalling processes associated with tissue reorganization. Early veligers markedly accumulate DPA likely in response to low docosahexaenoic acid (22:6ω3, DHA) concentrations in the three tested diets. The potential role and effect of DPA as a substitute for DHA is discussed.     

Divergent responses of Atlantic cod to ocean acidification and food limitation

In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end‐of‐century levels of ocean acidification. Here, we analysed larval growth among 35–36 days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO₂ treatments (ambient: 503 µatm, elevated: 1,179 µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO₂ treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO₂ treatment compared to the ambient CO₂ treatment. However, the elevated CO₂ group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade‐off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish.     

Suppression of microzooplankton by zebra mussels: importance of mussel size

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22-mm in size on Lake St Clair microzooplankton (< 240)μm) in laboratory experiments. 2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer-based clearance rates of large (22 mm) mussels approached published values for phytoplankton food. 3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns.     

The suitability of the free-living nematode Panagrellus redivivus as live food for first-feeding fish larvae

The free‐living nematode Panagrellus redivivus has been recommended as a suitable food source for first‐feeding fish. A new technology for mass production of P. redivivus enables fish hatchery operators to rely on an inexpensive, standardized and permanently available live food for first‐feeding fish larvae. The proximate composition, and the fatty acid and amino acid profiles of nematodes mass produced on oat‐based and purified ingredient media were determined. The quality of nematodes was significantly influenced by the culture medium used. The lipid content and fatty acid composition of nematodes could be modified by using lipid‐enriched media. Mass‐produced nematodes were tested on first‐feeding common carp (Cyprinus carpio L.) and whitefish (Coregonus lavaretus) larvae. Carp larvae, grown on nematodes cultured on oat medium enriched with sunflower oil, showed a higher survival rate (87.1%) than the control group fed frozen zooplankton (82.9%) at the end of the 1‐week feeding experiment. Differences in larval mass between the treatments disappeared after subsequent feeding of a dry diet for 2 weeks. Whitefish larvae can be reared exclusively on a dry diet; here, the initial feeding of nematodes had no effect on final biomass and survival of larvae.     

Effects of different food on growth and survival of first‐feeding taimen Hucho taimen (Pallas, 1773) larvae

A study was conducted to compare growth and survival of Hucho taimen larvae from 21 to 76 days after hatch (DAH) fed one of three diets: formulated feed alone (group F); a co‐feeding diet of water fleas, tubifex and formulated feed (group C); or live food of water fleas and tubifex (group L), and to investigate the potential use of dietary L‐alanyl‐L‐glutamine (L‐AG) in larval taimen for a more nutritious starter diet. Triplicate groups of 5000 fish were randomly assigned to each aquarium provided with water from a flow‐through system, and fed to apparent satiation. The results show that larvae can feed efficiently on floating crumbled particles of formulated feed. Weight gain of larvae fed only formulated feed was significantly lower than other groups at 34 DAH (P < 0.05). At the end of the experiment, weight gain reached the highest value in group F and was lowest in group L (P < 0.05). Condition factor reached the highest values in group F and lowest in group C (P < 0.05). Specific growth rate was in accordance with weight gain at 76 DAH. Survival showed no differences among the groups (P > 0.05). In conclusion, H. taimen larvae can be fed formulated feed alone and L‐AG may be used as a feeding attractant during the weaning process, which should lead to a better understanding in the rearing improvement in the feeding of larvae.     

Diet of marine fish larvae and juveniles that use rocky intertidal pools at the Portuguese coast

The use of tidal pools during early ontogeny is likely to enhance growth, condition and survival chances of the transient marine fish larvae and juveniles that use them. However, the diet of such individuals within tidal pools is poorly known; this knowledge is important to understand why such high numbers of individuals use these environments in spring and summer on the Portuguese coast. Transient marine fishes were sampled monthly over a two‐year period in four tidal pools of a rocky reef on the west Portuguese coast. The diet composition in the tidal pools of the most abundant marine fish larvae/juveniles, Diplodus sargus and Atherina spp., were investigated. Stomach and gut contents of 483 individuals (354 D. sargus ranging in total length from 9 to 87 mm and 134 Atherina spp. ranging in total length from 10 to 31 mm) were analyzed and dietary indices estimated for the different developmental stages. The diet of D. sargus composed mainly harpacticoid copepods, chironomid larvae, ostracods, chironomid adults and amphipods; whereas the diet of Atherina spp. was mainly harpacticoid copepods, ostracods and gastropods. Along the ontogenetic development, the proportions and diversity of food items in the D. sargus diet varied. Importance of the harpacticoid copepods decreased with increasing fish size, while that of amphipods and isopods increased. Larvae and juvenile D. sargus and Atherina spp. found in rocky reef tidal pools are opportunistic consumers of a wide range of prey and thus take advantage of the high prey availability in these habitats.     

Food assimilation of a neotropical riverine detritivorous fish, Prochilodus lineatus, studied by fatty acid composition (Pisces, Curimatidae)

Food assimilation by the detritivorous fish Prochilodus lineatus, throughout a life cycle, was studied by means of fatty acid analysis. Fish length ranged from 2.7 to 55 cm and weight from 2 to 2670 g. Samples for fatty acid determination were taken from the mesenteric deposit in adults and from the whole fish in juveniles. Phyto and zooplankton, and superficial mud were also studied. Samples were taken from the principal channel of the Paraná River and lentic environments in its alluvial plain (60 ° 29W and 31 ° 40S). Fatty acids in the smaller fish (2.8–3.8 cm) indicated the assimilation of zoo and phytoplankton. Longer P. lineatus have a fat-deficient diet, particularly in polyunsaturated acids. At different stages of life, P. lineatus is adapted to different sources of food. When young, it eats zoo- and phytoplankton, becomes gradually detritivorous and has a series of adaptations of the digestive tract (morphological and histological) to enable it to assimilate detritus.     

Improvement of nutritional quality of cultured sobaity sea bream,Sparidentex hasta (Valenciennes) muscle by preharvest feeding of finisher feeds

A 6‐month long study was conducted to improve the nutritional quality of the cultured sobaity bream, Sparidentex hasta by feeding them finisher feeds containing high docosahexaenoic acid (DHA) at the last two months of the grow‐out stage so that the muscle DHA level be increased at par to the wild. A grow‐out feed used from the beginning until the end of the trial was considered as the control (Diet 1). Experimental diets 2 and 3 were formulated to contain 9.0% DHA (e.g. 1.68 g DHA/100 g feed) and 10.5% DHA (2.20 g DHA/100 g feed), by incorporating high DHA tuna oil into a sea bream grow‐out diet. For comparison, a commercial finisher feed (Diet 4) from Skretting, Italy was also used. The results of this study demonstrated that fish fed DHA enriched finisher diets resulted in significantly (p < .05) better growth, feed utilization and higher muscle eicosapentaenoic acid (EPA) and DHA content compared to those fed grow‐out diet. The muscle DHA and EPA of fish fed finisher diets were also higher than those of the whole year average DHA and EPA content of wild sobaity. An organoleptic evaluation showed no significant (p > .05) differences between sensory attributes of muscle from cultured and wild sea bream. The results of the study demonstrated that feeding finisher feed enriched with DHA at the later part of the grow‐out operation, the n‐3 PUFA levels of cultured sobaity can cost‐effectively be increased at par to the wild.     

Spatiotemporal occurrence and feeding habits of tonguefish,Cynoglossus lighti Norman, 1925, larvae in Ariake Bay,Japan

Spatiotemporal occurrence and feeding habits of tonguefish (Cynoglossus lighti Norman, 1925) larvae were investigated in an offshore area (>5 m in depth) of the inner part of Ariake Bay, Japan. All specimens were symmetric, free‐swimming larvae. Although their seasonal abundance and distribution in the study site varied from year to year, spawning started in June and the larval abundance was high in August and September with a wide distribution in the inner part of the bay. Both present and previous study results strongly suggest that larvae may settle primarily in the estuary and near‐shore areas of Ariake Bay after their wide distribution in the offshore area of the bay during the free‐swimming stage. Larvae showed a clear feeding rhythm in which they fed on prey mainly during the daytime. Larvae fed exclusively on copepods, and identified prey were mostly Paracalanidae (mainly Parvocalanus crassirostris), Microsetella norvegica, and Oithona davisae. Pre‐metamorphosis larvae fed primarily on Paracalanidae and O. davisae, whereas O. davisae formed a smaller proportion of the early‐metamorphosis diet. In early metamorphoses, larvae fed preferentially on Paracalanidae and M. norvegica.     

Ontogenetic diet shifts produce trade‐offs in elemental imbalance in bluegill sunfish

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