Small-sized Fish Research Articles

Diversity of demersal fish in the East China Sea: Implication of eutrophication and fishery

The environment of the East China Sea has been greatly impacted by both fishing and land-based pollution over the past decades, with a concomitant decline of fishery resources. Imposition of a seasonal fishing moratorium and a trawling prohibition zone has failed to engender recovery of fish communities. To help understand the respective impacts of environmental factors and fishing activities in the East China Sea ecosystem, fish samples and environmental parameters were collected in prohibited and open fishing areas, during the seasonal fishing moratorium. The inshore area of the East China Sea, corresponding to the prohibited zone for trawling, had extremely high nutrient concentrations and relatively low dissolved oxygen. The diversity index of demersal fish showed significantly negative correlations with nutrient concentrations and positive correlations with bottom-water dissolved oxygen. The inshore area of the East China Sea was heavily dominated by small-sized fishes, such as Gobiids—Amblychaeturichthys hexanema and Apogonids—Apogon lineatus, reflecting low survival of most fish species. In contrast, the offshore areas, with lower nutrient concentrations and higher dissolved oxygen, had higher biodiversity. These findings suggest that eutrophication and subsequent hypoxia is responsible for the limited recovery of fishery resources in the trawling prohibition area of the East China Sea. Therefore, a multi-pronged fishery management that involves both fishing restriction and environmental improvement is urgently needed in the East China Sea.

Composição da ictiofauna em ambientes marginais e tributários do médio-submédio rio São Francisco

The middle and lower stretches of the São Francisco River are the most affected by the construction of hydroelectric dams, with over 550 km dammed. Despite of impact of dams on fish composition and distribution, the ichthyofauna of theses stretches is the least known of the entire river basin. The present study aimed at characterizing the fish assemblages of nine marginal lakes, three temporary ponds and 12 streams and rivers, located betweenthe municipalities of Barra (BA) and Belém do São Francisco (PE), during the rainy and dry periods, between September 2006 and September 2009. Sixty-one species distributed among Characiformes (39 species), Siluriformes (8), Perciformes (7), Cyprinodontiformes (3); Gymnotiformes (2); Clupeiformes  and Synbranchiformes (1 each) were identified. Fish assemblages were composed of small-sized fish, 76% of them with SL < 100 mm, and the remaining with SL between 100 and 180 mm. Despite the importance of flooded environments for rheophilic fish, only 12 migratory species were recorded. The ichthyofauna of the environments studied is predominantly composed of small-sized and resident invertivores, invertivores and omnivores occurred in alltributaries, whereas most herbivores were recorded in ponds.

Fatty Acid Profile of Indian Shad Tenualosa ilisha Oil and its Dietary Significance

Polyunsaturated fatty acids (PUFAs) consumption is known to be associated with a number of health benefits and fish oils, especially marine, are rich in PUFAs. Tenualosa ilisha, a highly preferred food fish in South-Asian countries, is rich in oils; however, information on fatty acid profiles of different size-groups of hilsa is scanty. In the present investigation, information on fatty acid profiles of different size groups of hilsa has been generated. Analysis showed that medium-sized fish contained the highest amount of unsaturated fatty acids as well as ω-3 PUFAs, EPA plus DHA and the lowest amount of saturated fatty acids (SFAs). PUFA content was highest in small-sized hilsa; however, ω-3 PUFA content was lower and SFAs content was higher than medium-sized fish. In large-sized fish, although ω-3/ω-6 ratio was highest, quantitatively they contained the lowest amount of PUFAs and highest amount of SFAs. Thus, on basis of fatty acid profiles, medium-sized hilsa is the best followed by the small-sized fish for human health and nutrition.

The past, present and projected scenarios in the Lake Albert and Albert Nile fisheries: Implications for sustainable management

Lake Albert is one of the largest lakes in Uganda that still supports a multi-species fishery which as a result of variable adult sizes of the species, causes management challenges especially in relation to gear mesh size enforcement. Prior to the 1980s, commercial species were 17 large sized fishes especially Citharinus citharinus, Distichodus niloticus and Lates spp. that were confimed to inshore habitats of the lake and were thus rapidly over fished. Frame and catch assessment surveys conducted in this study revealed a >80% dominance of small size fish species (Neobola bredoi and Brycinus nurse) and a 40 -60% decrease in the contribution of the large commercial species. Sustainability of small size fish species is uncertain due to seasonal fluctuations and low beach value. At about 150,000 tons of fish recorded from Lake Albert and Albert Nile, the beach value was estimated at 55.3 million USD. Despite the noted decline in catches of the large sized fishes their contribution was more than 50% of total beach value. Therefore, management measures should couple value addition for the small sized species and maintain effort regulation targeting recovery of the large previously important commercial species.

北部湾秋季底层鱼类多样性和优势种数量的变动趋势

根据1992年、2001年和2006年秋季在北部湾进行的底拖网调查数据,对该海域鱼类的种类组成、物种多样性、优势种及其数量的变动趋势进行分析。1992年共记录鱼类171种,隶属17目77科;2001年记录鱼类156种,隶属18目71科;2006年记录157种,隶属17目67科。3个年代记录的鱼类均以鲈形目的种类数最多,其中1992年为96种(占56.14%)、2001年90种(占57.69%)和2006年89种(占56.69%)。鱼类的Pielou均匀度指数(<em>J'</em>)和Shannon-Wiener多样性指数(<em>H'</em>)的变化趋势一致:以2001年最高,为0.72和3.64;其次为1992年,为0.64和3.27;2006年最低,分别为0.52和2.64。丰富度指数(<em>D</em>)呈逐年下降的趋势:为1992年的21.03,2001年的20.74和2006年的19.61。建立非线性回归模型对北部湾3个年代出现的6种共有优势种(发光鲷<em>Acropoma japonicum</em>、带鱼<em>Trichiurus haumela</em>、二长棘鲷<em>Parargyrops edita</em>、黄斑鲾<em>Leiognathus bindus</em>、竹荚鱼<em>Trachurus japonicus</em>和黄带绯鲤<em>Upeneus sulphureus</em>)的数量变化趋势进行分析。结果表明:北部湾鱼类中的经济价值较高的优势种逐渐被低值和小型的鱼类所替代,但繁殖力较强和寿命较短的鱼类变动较小。在6种共同优势种中,黄斑鲾和发光鲷的渔获率呈上升趋势;带鱼和黄带绯鲤的渔获率呈下降趋势;而二长棘鲷和竹荚鱼的渔获率基本保持不变。研究结果表明,北部湾鱼类的优势种更替明显,总体变化趋势是<em>k</em>选择种类(以红笛鲷和黑印真鲨等为代表)逐渐被<em>r</em>选择种类(发光鲷、鲾科和天竺鱼科等为代表)所替代,即寿命长、个体大和营养级高的鱼类数量减少,寿命短、个体小和营养级较低的种类增多。;The Beibu Gulf is a semi-enclosed gulf located in the northwestern South China Sea and surrounded by the land territories of China and Vietnam. The region has a tropical to subtropical climate. Thousands of fish and shellfish species have been identified in the Beibu Gulf and support some very important fisheries throughout the year in the region. Large scale resource surveys have been conducted over the last few decades to assess fisheries resources in the Beibu Gulf, and a large quantity of biological and environmental data have been collected. Such scientific data are perfect for evaluating changes in the ecosystem and answers questions such as what changes have occurred over the last few decades to the fisheries ecosystem in the Beibu Gulf? In the study, we analyzed data collected in otter trawl surveys in the Beibu Gulf in autumn 1992, 2001 and 2006 to evaluate fish species composition and diversity, dominant species, and their biomasses. The analysis showed that 171 fish species caught in the 1992 autumn survey in the Beibu Gulf Gulf belonged to 77 families and 17 orders, a total of 156 fish species belonging to 71 families and 18 orders were found in the 2001 survey and 157 species belonging to 67 families and 17 orders were identified in 2006. Perciformes had the highest number of fish species, 96 species (accounting for 56.14%) in 1992, 90 species (57.69%) in 2001 and 89 species (56.69%) in 2006. The Pielou evenness index (<em>J'</em>) had the same temporal trend as the Shannon-Wiener diversity index (<em>H'</em>). Both indices were the highest in 2001, followed by those in 1992 and 2006. The Margalef richness index (<em>D</em>) reduced from 21.03 in 1992 to 20.74 in 2001 and to 19.61 in 2006. Nonlinear regression models were developed to quantify the temporal trends of biomass of the 6 dominant species (<em>Acropoma japonicum</em>, <em>Trichiurus haumela</em>, <em>Parargyrops edita</em>, <em>Leiognathus bindus</em>, <em>Trachurus japonicas</em> and <em>Upeneus sulphureus</em>) in the Beibu Gulf. The dominant species were found to shift from the high-value fish species to the low-value species, but no significant changes for fish species with high reproduction rates and short life spans. The catch rates increased during the survey period for <em>A. japonicum</em> and <em>L. bindus</em>, decreased for <em>T. haumela</em> and <em>U. sulphureus</em>, and remained similar for <em>P. edita</em> and <em>T. japonicus</em>. This study shows an apparent succession of the dominant species with an overall trend of the K-selection species (such as <em>Lutjanus sanguineus</em> and <em>Carcharhinus menisorrah</em>) being replaced by the <em>r</em>-selection species (such as <em>A. japonicum</em>,<em>Leiognathus</em>, and <em>Apogonichthys</em>). The abundance of fish species with long life span, large size and high trophic levels decreased, while short-lived and small-sized fish species in low trophic levels increased their abundance over the time period covered by the survey. The study provides important evidence of changes occurring in the Beibu Gulf ecosystem.

Importance of lateral lagoons for the ichthyofauna in a large tropical reservoir

This study aimed to analyse the composition and the ecological attributes of small-sized fish assemblages in four lagoons and in the main channel of Rosana Reservoir (SE Brazil). Fieldwork was carried out in September and November/2004 and January, March, May and August/2005. In each sampling station and period five manual throws were performed towards aquatic macrophyte stands, using a hand net (1.5 × 5 m; 0.3 cm of mesh size). The ichthyofauna collected was represented by 42 species, totalizing 3,424 individuals, 2,186 g in weight. The order Characiformes was dominant, mainly in the lagoons with low connectivity with the river. The main taxon (Importance Index) was Hemigrammus marginatus. Higher richness, abundance, biomass, diversity and lower individual mean length were observed in the lagoons, especially during the rainy period. Spatial segregation of some species was showed by the canonical correspondence analysis indicating the habitat complexity. The results validate the hypotheses that lateral lagoons have a prominent ecological role in the life cycle of juveniles and small fish and demonstrate how the connectivity river/lagoons may be important for assemblages maintenance.

The response of Grey Herons Ardea cinerea to changes in prey abundance

Capsule Herons responded to the lower abundance of a preferred fish by switching prey. Aims To investigate how Grey Herons respond to the decline in abundance of a preferred fish, the Round Goby Neogobius melanostomus. Methods Grey Herons Ardea cinerea breeding in the Gulf of Gdańsk area (Baltic Sea) were the study population. Regurgitated food and pellets were analysed. Biomass and abundance of fish was compared between 2000–02 (when the population of Round Goby was increasing) and 2008–09 (when the Round Goby population stabilized). Results The abundance and biomass of Round Goby preyed upon by herons decreased from between 95 and 99% in 2000–02 to between 38 and 56% in 2008–09. Energy-rich salmonids, not recorded in 2000–02, were an important diet component in 2008–09 (42% of biomass). Small-sized fish abundance was higher in 2008–09 (37%) than in 2000–02 (9%). Conclusions Grey Herons in 2008–09 adapted to the lower availability of Round Gobies by prey switching to other available fish – abundant but small-sized Three-spined Sticklebacks Gasterosteus aculeatus and less abundant but more profitable salmonids (easy to catch in the case of hatchery-reared, tagged individuals). Diet composition suggests that Grey Herons in 2008–09 exploited more diverse foraging areas (dry habitats, woods, garden ponds) than in 2000–02.

Paratenic hosts as regular transmission route in the acanthocephalan Pomphorhynchus laevis: potential implications for food webs

Although trophically transmitted parasites are recognized to strongly influence food-web dynamics through their ability to manipulate host phenotype, our knowledge of their host spectrum is often imperfect. This is particularly true for the facultative paratenic hosts, which receive little interest. We investigated the occurrence and significance both in terms of ecology and evolution of paratenic hosts in the life cycle of the fish acanthocephalan Pomphorhynchus laevis. This freshwater parasite uses amphipods as intermediate hosts and cyprinids and salmonids as definitive hosts. Within a cohort of parasite larvae, usually reported in amphipod intermediate hosts, more than 90% were actually hosted by small-sized fish. We demonstrated experimentally, using one of these fish, that they get infected through the consumption of parasitized amphipods and contribute to the parasite's transmission to a definitive host, hence confirming their paratenic host status. A better knowledge of paratenic host spectrums could help us to understand the fine tuning of transmission strategies, to better estimate parasite biomass, and could improve our perception of parasite subwebs in terms of host-parasite and predator-parasite links.

Methyl mercury in fish—a case study on various samples collected from Ganges river at West Bengal

This study investigated the presence of total mercury (Hg) and organic mercury levels in the muscle of 19 common fresh water fish species captured from river Ganges, West Bengal, India. The total mercury level found in our study may not cause any toxic effect, but the methyl mercury (MeHg) level in some freshwater fish species was surprisingly very high and toxically unacceptable. The results of mercury analysis in various specimens indicated that some fish muscles tended to accumulate high levels of Hg, and approximately 50-84% of Hg was organic mercury. A strong positive correlation between mercury levels in muscle with food habit and fish length (age) was found. Wallago attu possessed the highest amount of organic mercury in their muscle tissues, and it was 0.93 ± 0.61 μg Hg/g of wet weight. Whereas in small-sized fishes Eutropiichthys murius, Puntius sarana, Cirrhinus mrigala, Mystus vittatus or Mystus gulio, and Tilapia mossambicus, it was below the detection limit. Contamination in Catla catla (0.32 ± 0.11), Anguilla bengalensis bengalensis (0.26 ± 0.07 μg Hg/g), Chitala chitala (0.25 ± 0.18), Rita rita (0.34 ± 0.14), and Ompok pabda (0.26 ± 0.04) was also above the 0.25 μg Hg/g of wet weight, the limit set by the PFA for the maximum level for consumption of fish exposed to MeHg. Though in Labeo rohita (0.12 ± 0.03), Mastacembelus armatus (0.17 ± 0.02), Pangasius pangasius (0.12 ± 0.16), Bagarius bagarius (0.12 ± 0.01), and Clupisoma garua (0.1 ± 0.01), concentration was below the recommended level, in Lates calcarifer (0.23 ± 0.0) and Mystus aor (0.23 ± 0.1), it was threatening. Interestingly, a low concentration of Hg was found in post-monsoon samples.

Parasite fauna of farmed Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) in Uganda

An intensive parasite survey was conducted in 2008 to better understand the parasite fauna occurrence, distribution and diversity in the commercial aquaculture fish species in Uganda. A total of 265 fish collected from hatcheries and grow-out systems were examined for parasites using routine parasitological techniques. The survey yielded 17 parasite species: 11 from Oreochromis niloticus and ten from Clarias gariepinus. Four parasites-Amirthalingamia macracantha, Monobothrioides sp., Zoogonoides sp. and a member of the family Amphilinidae-were recorded for the first time in the country. The parasite diversity was similar between hosts; however, O. niloticus was dominated by free-living stage-transmitted parasites in lower numbers, whereas both trophically and free-living stage-transmitted parasites were equally represented in C. gariepinus in relatively high intensities. The patterns in parasite numbers and composition in the two hosts reflect differences in fish habitat use and diet. A shift in parasite composition from monoxenous species-dominated communities in small-sized fish to heteroxenous in large fishes was recorded in both hosts. This was linked to ontogenetic feeding changes and prolonged exposure to parasites. Polyculture systems showed no effect on parasite intensity and composition. The gills were highly parasitized, mainly by protozoans and monogeneans. Generally, the occurrence and diversity of parasites in these fish species highlight the likelihood of disease outbreak in the proposed intensive aquaculture systems. This calls for raising awareness in fish health management among potential farmers, service providers and researchers.

The role of the European bitterling (Rhodeus amarus, Cyprinidae) in parasite accumulation and transmission in riverine ecosystems

In aquatic ecosystems, fish play a key role in parasite accumulation and transmission to predacious animals. In the present study, realized on seven populations of a small cyprinid fish species, the European bitterling Rhodeus amarus, we investigated (1) the role of the European bitterling as a potential intermediate or paratenic host, (2) the ability of the fish to accumulate parasites with similar final host group, and (3) its significance as a potential source of parasite infection in the ecosystem in respect to habitat characteristics. A total of 36 parasite species were recorded; 31 species (90% of all parasite specimens) were classified as endoparasites. Most of the endoparasites were found in the larval life stage, using bitterling as an intermediate or paratenic host. In particular, parasite community structure showed significantly higher proportions of allogenic parasites in comparison with autogenic. The supposed co-occurrence of parasite species with identical final host groups showed only a weak association. The adjacent reservoir areas were a significant determinant of both the total and infracommunity parasite species richness and for the mean parasite abundance. No relationship between the distance of sampling site from the adjacent reservoir and parasite community characteristics was found. As a small-sized fish with a wide distribution range and high local abundances, the European bitterling can represent a natural prey for a wide range of piscivorous predators. Due to its susceptibility to the number of larval endoparasites, this fish species may therefore fulfill the role as important transmitter of parasites to their final hosts.

Health status of native fish (Percilia gillissi and Trichomycterus areolatus) downstream of the discharge of effluent from a tertiary‐treated elemental chlorine‐free pulp mill in Chile

Few data exist on the possible effects of pulp and paper effluent discharge on native fish populations in the Southern Hemisphere, relative to the research done in the Northern Hemisphere. The present research examined two native fish species (Trichomycterus areolatus and Percilia gillissi) for effects at both the molecular and individual level due to the discharge of effluent from a tertiary treated elemental chlorine-free pulp mill into a fluvial system in Central Chile over three seasons (February 2007, October 2007, January 2008). Different responses were observed between species and between sexes. There was an increase in the production of gonadal 17β-estradiol in the females of both species but a drop in 11-ketotestosterone production in P. gillissi males. Female gonadal size was increased, especially during the summer period, with corresponding increases the frequency of advanced oocyte development, and in the oocyte diameter in both species. Hepatic ethoxyresorufin-O-deethylase (EROD) activity was elevated for both species downstream of the discharge point, although overall it was higher in P. gillissi than T. areolatus. Decreases in the frequency of smaller-sized fish for both species, as well as a drop in the size of the adults downstream of the discharge point, were observed. The present study is the first evidence of endocrine disruption in native freshwater fish associated with modern pulp mills in South America. This study establishes possible links in the reproductive alterations observed at the subindividual and individual levels that could explain the changes observed at the population level.

Patterns of species richness and composition of fish assemblages in streams of the Ivinhema River basin, Upper Paraná River

AIM: The present study analyzed the spatial variation in fish species richness and composition in streams of the Ivinhema River basin, Upper Paraná basin, determining the relationship between local and regional descriptors of the fish assemblage organization; METHOD: From 2001 to 2011 we sampled 200 stream stretches, using different sampling methods. Local species richness and composition were analyzed using univariate and multivariate methods to detect patterns of variation in the fish assemblage organization; RESULTS: We identified 111 fish species in the streams, and estimated the occurrence of 117 fish species (CIα0.05 = 111 to 123) with lower species richness in headwater streams compared to the lower parts of the basin. The fish species recorded were predominantly of small size, and the mean size increased from the headwaters to the river mouth. The four most common species are widely distributed in the basin. However, 24 species are allocthonous to the Upper Paraná basin, and two species (Chaetobranchopsis australis and Apistogramma commbrae) are recorded here for the first time in the Upper Paraná basin. Altitude was the main determinant of local fish species richness and composition, and a discontinuity in assemblage organization (richness, composition, fish size) was detected at approximately 430 m a.s.l.; CONCLUSION: Streams of the Ivinhema River basin are inhabited mainly by small-sized fishes; and longitudinal variation, interacting with local characteristics, determines the fish assemblage patterns.

이각망에 채집된 2008년 태안 연안 어류 종조성

The species and size compositions of fishes in the coastal waters off Taean were determined using samples collected with a two-sided fyke net in 2008. A total of 22 species, 2,371 individuals and 1,351 kg of fish were collected during the study. Of the fish collected, semi-benthic fishes such as Sebastes schlegelii, Mugil cephalus and Chelon haematocheilus were the most abundant (77.5% and 76.4% for total number of individuals and biomass, respectively). Benthic fishes such as Pleuronectus yokohamae and Paralichthys olivaceus were collected in almost all seasons but were low in abundance (5.3% and 4.1% for total number of individuals and biomass, respectively). Seasonal migrants were plentiful; specifically, Seriola quinqueradiata was abundant in November while Konosirus punctaus was common in July. Seasonal migrants of small-sized fish have been known to be abundant in the coastal water of western Korea including the study area, but few fish less than 100 mm were collected due to the large mesh size (30 mm) of the net used.

5S rDNA chromosomal mapping and COI sequence analysis reveal differentiation among distinct populations of a characid fish Serrapinnus notomelas

Cheirodontinae comprises a small-sized fish group with a wide geographical distribution throughout Central and South America, mainly in Brazilian Basins. The species Serrapinnus notomelas is widely distributed in the Upper Parana River Basin. In this work, chromosomal mapping of 5S ribosomal RNA (rRNA) gene was performed trough fluorescence in situ hybridization (FISH) in speciemens from three distinct localities belonging to two basins in the Sao Paulo State. All populations presented 5S clusters in two chromosome pairs. One additional pair was detected in samples from the Rio Paraitinguinha (Tiete Basin), and two additional pairs were detected in the population from Corrego Campo Novo (Tiete Basin). Analyses with partial sequences of COI were performed to verify the interelationship among the studied specimens, revealing Corrego Campo Novo population as a sister-group to the clade formed by the two other populations. The samples from Rio Paraitinguinha and Recanto dos Cambaras presented two distinct haplotypes each, while five haplotypes were observed in the Corrego Campo Novo population, sugesting that this could be older than the other populations. None of the nine haplotypes were shared among the three populations. The similarities and differences observed among the three populations using cytogenetic data and COI analysis are not related to geographic distances that separate the samples, suggesting that the origin of the Rio Paraitinguinha and Recanto dos Cambaras populations may be related to faunal exchanges. Additionally, the present data suggest that the analyzed populations of S. notomelas may be on independent evolutionary trajectories but in a very initial diversification stage. Moreover, the use of integrative information, such as molecular and chromosomal data in the analysis of population divergence and evolutionary trajectories in freshwater fishes is reinforced.

Temperature-Driven Regime Shifts in the Dynamics of Size-Structured Populations

Global warming impacts virtually all biota and ecosystems. Many of these impacts are mediated through direct effects of temperature on individual vital rates. Yet how this translates from the individual to the population level is still poorly understood, hampering the assessment of global warming impacts on population structure and dynamics. Here, we study the effects of temperature on intraspecific competition and cannibalism and the population dynamical consequences in a size-structured fish population. We use a physiologically structured consumer-resource model in which we explicitly model the temperature dependencies of the consumer vital rates and the resource population growth rate. Our model predicts that increased temperature decreases resource density despite higher resource growth rates, reflecting stronger intraspecific competition among consumers. At a critical temperature, the consumer population dynamics destabilize and shift from a stable equilibrium to competition-driven generation cycles that are dominated by recruits. As a consequence, maximum age decreases and the proportion of younger and smaller-sized fish increases. These model predictions support the hypothesis of decreasing mean body sizes due to increased temperatures. We conclude that in size-structured fish populations, global warming may increase competition, favor smaller size classes, and induce regime shifts that destabilize population and community dynamics.

Small-sized Fish Assemblages Do not Differ Between a Native and a Recently Established Non-indigenous Macrophyte in a Neotropical Ecosystem

Hydrilla verticillata recently invaded a protected area in the Upper Parana River floodplain. In a rare opportunity, when this non-indigenous species co-occurred with the native Egeria najas in a secondary channel of the river, we assessed its effects on assemblage of small-sized fish. Traps were used to catch fish inside macrophyte patches in periods of low and high water. We assessed fish abundance, biomass, diversity, richness and the community composition (using a DCA). The number of fish species did not differ between plants. Fish abundance and biomass were significantly higher during the low water period but plant species did not affect these attributes. Similarly, fish assemblage composition differed only between seasons. Our results indicate that the oscillations in the water level had a greater effect on the small-sized fish assemblage than the presence of the non-indigenous macrophyte. In addition, H. verticillata favors small fish assemblages such as the native does; however, we contend that our conclusions are valid only for habitats scarcely colonized by native plant species. The invasion of other habitats colonized by a high diversity of native species of macrophytes, which are key for small-sized fish, is a matter of concern.

A network-based approach to the analysis of ontogenetic diet shifts: An example with an endangered, small-sized fish

Many organisms exhibit ontogenetic shifts in their diet and habitat use, which often exert a large influence on the structure and expected dynamics of food webs and ecological communities. Nevertheless, reliable methods for detecting these niche shifts from consumption data are limited. In this study we present a new approach for the detection and analysis of ontogenetic diet shifts, based on complex network theory. As a case study, we apply these methods to the endangered, small fish Aphanius iberus. The stage-structured consumer population and its set of consumed prey are represented as an unweighted bipartite network. A statistical evaluation of the resulting network structure permits to uncover empirical patterns of ontogenetic diet shifts. We test for changes in niche breadth, as well as nestedness and diet modularity along ontogeny. These tests were carried out on the subnetworks describing consumption, positive electivity, and negative electivity on prey items. The statistical significance was established by means of null model analyses. Our analyses reveal a nested diet, along with a gradual decrease in diet breadth and a modular structure (i.e. abrupt changes) of elected preys along the ontogeny of A. iberus. The detection of network structure by means of the use of tools from complex network theory is shown to be a promising method for studying ontogenetic niche shifts.

Circadian Rhythms of Self-feeding and Locomotor Activity in Zebrafish (Danio Rerio)

To investigate daily feeding rhythms in zebrafish, the authors have developed a new self-feeding system with an infrared photocell acting as a food-demand sensor, which lets small-size fish such as zebrafish trigger a self-feeder. In this paper, the authors used eight groups of 20 fish. Locomotor activity rhythms were also investigated by means of infrared sensors. Under a 12 h:12 h light (L)-dark (D) cycle, zebrafish showed a clear nocturnal feeding pattern (88.0% of the total daily food-demands occurring in the dark phase), concentrated during the last 4 h of the dark phase. In contrast, locomotor activity was mostly diurnal (88.2% of total daily activity occurring in the light phase). Moreover, both feeding and locomotor rhythms were endogenously driven, as they persisted under free-running conditions. The average period length (τ) of the locomotor and feeding rhythms was shorter (τ = 22.9 h) and longer (τ = 24.6 h) than 24 h, respectively. During the time that food availability was restricted, fish could only feed during ZT0–ZT12 or ZT12–ZT16. This resulted in feeding activity being significantly modified according to feeding time, whereas the locomotor activity pattern remained synchronized to the LD cycle and did not change during this trial. These findings revealed an independent phasing between locomotor and feeding activities (which were mostly nocturnal or diurnal, respectively), thus supporting the concept of multioscillatory control of circadian rhythmicity in zebrafish. (Author correspondence: javisan@um.es)

First record of a clupeomorph fish in the Neuquén Group (Portezuelo Formation), Upper Cretaceous of Patagonia, Argentina

A new genus and species of clupeomorph fish, Leufuichthys minimus, is described from the fluvial deposits of the Portezuelo Formation, Upper Cretaceous (Turonian–Coniacian) of the Neuquén Group, Patagonia, Argentina. It is a small-sized fish with an estimated body length up to 46mm. Among other characters, the new species shows the following: abdominal scutes; abdomen moderately convex; anal fin elongate-based; three uroneurals; two epurals; caudal fin bearing very elongate rays; and cycloid scales. Leufuichthys minimus gen. et sp. nov. shows a greater similarity with Kwangoclupea dartevellei, a clupeomorph described from a marine Cenomanian deposit of the Democratic Republic of Congo (Africa), mainly due to the presence of an elongate-based anal fin, bearing more than 20 fin-rays, differing from it by the presence of a not hypertrophied abdomen. As far as known, L. minimus gen. et sp. nov. is the first clupeomorph described in the Upper Cretaceous of Patagonia and represents one fortuitous preservation of an articulated fish in fluvial deposits.