Trophic complexity of small fish in nearshore food webs

Small nearshore fishes are an important part of lacustrine and functional diversity and link pelagic and benthic habitats by serving as prey for larger nearshore and offshore fishes. However, the trophic complexity of these small nearshore fishes is often unrecognized and detailed studies of their role in food webs are lacking. Here, we examined niche space patterns of small nearshore fish species using Bayesian analyses of carbon and nitrogen stable isotope data in nine freshwater lakes that are among the largest lakes in Minnesota. We found considerable variability in niche areas within species and high variability in niche overlap across species. At the assemblage level, niche overlap (average diet overlap of all species pairs at a lake) decreased as whole-lake species richness increased, possibly indicating a greater degree of resource specialization in more speciose lakes. Overall fish niche space was weakly but significantly related to niche space of their invertebrate prey. Although nearshore benthic resources contributed to fish diets in all lakes, all fish species also had non-negligible and variable contributions from pelagic zooplankton. This inter- and intraspecific variability in trophic niche space likely contributes to the multi-level trophic complexity, functional diversity, and potentially food web resilience to ecosystem changes.

     

The lipid compositions of high-Antarctic notothenioid fish species with different life strategies

Lipid and fatty acid compositions of five notothenioid fishes from the Antarctic Weddell and Lazarev Seas were investigated in detail with regard to their different modes of life. The pelagic Aethotaxis mitopteryx was the lipid-richest species (mean of 61.4% of dry mass, DM) followed by Pleuragramma antarcticum (37.7%DM). The benthopelagic Trematomus lepidorhinus had an intermediate lipid content of 23.2%DM. The benthic Bathydraco marri (20.8%DM) and Dolloidraco longedorsalis (14.5%DM) belonged to the lipid-poorer species. Triacylglycerols were the major lipid class in all species. Important fatty acids were 16:0, 16:1(n-7), 18:1(n-9), 18:1(n-7), 20:5(n-3) and 22:6(n-3). The enhanced proportions of the long-chain monounsaturated fatty acids, 20:1 and 22:1, in the lipid-rich pelagic fishes clearly reflected the ingestion of the two copepod species, Calanoides acutus and Calanus propinquus, which are the only known Antarctic zooplankters rich in these fatty acids. Although wax esters are the major storage lipid in many prey species, they were absent in all notothenioid fishes studied. Thus, wax esters ingested with prey are probably converted to triacylglycerols via fatty acids or metabolised by the fishes. The enhanced lipid accumulation with increasingly pelagic lifestyle has energetic advantages, especially with regard to improved buoyancy. It is still unknown to what extent these lipids are utilised as energy reserves, since it has been suggested that not only the benthic but also the pelagic Antarctic fishes are rather sluggish, with a low scope for activity and hence low metabolic requirements. Accepted: 14 May 2000     

Limited influence of a wind power project submarine cable on a Laurentian Great Lakes fish community

Previous research has identified the generation of electromagnetic fields (EMFs) emanating from renewable energy project transmission cables to be a potential stressor to aquatic communities. In this study, we investigated whether the presence of a high voltage submarine transmission cable affected the spatial pattern and composition of nearshore and offshore fishes at a Laurentian Great Lakes site. The transmission cable investigated in this study runs 7.8 km along the lakebed of Lake Ontario, carrying electricity from the Wolfe Island wind power project to the city of Kingston, Ontario. In autumn of 2011, both nearshore electrofishing and deeper‐water fisheries acoustic surveys were conducted along transects at varying distances to the cable. For both habitat types, no detectable effects of the cable on the fish community were found. Local habitat variables, including substrate or depth, were more important in explaining variation in fish density than proximity to the cable. Common species encountered during the surveys were round goby (Neogobius melanostomus) in the nearshore and alewife (Alosa pseudoharengus) in the deeper channel. American eel (Anguilla rostrata), thought to be an electromagnetically sensitive species, was also encountered during the surveys including in close proximity to the cable. More robust impact assessments require sampling fishes before a cable installation, over greater time frames (additional seasons or years), and habitats that support more diverse native assemblages.     

Factors influencing the characteristics of fish assemblages in a large subtropical marine embayment

Mean number of species and density of fishes in nearshore shallow waters of Shark Bay, a large subtropical embayment, were c . seven and 19.5 times greater in seagrass than over bare sand, where protection from predators and the abundance of potential invertebrate prey were less. The number of fish species and density of fishes over bare sand were lower in nearshore than offshore waters, where there was a greater amount of organic material and thus presumably a greater density of benthic macroinvertebrate prey. Species composition in vegetated and unvegetated habitats differed markedly, with species such as Monacanthus chinensis, Apogon rueppellii and Pelates quadrilineatus being largely confined to seagrass, whereas others such as Pseudorhombus jenynsii, Torquigener whitleyi and Engyprosopon grandisquama were found predominantly or exclusively over bare sand. The ichthyofauna in beds of Posidonia australis , in which the canopy is uniformly dense, differed in composition and comprised a greater number of species and density of fishes than that in Amphibolis antarctica , in which an open space is present beneath the terminal clusters of relatively short leaves. Species composition in the beds of both of these seagrass species underwent well defined cyclical changes, caused by out-of-phase sequential changes in the densities of certain species. Such changes were less common over bare sand, where the ichthyofaunal composition was more variable. The number of species and density of fishes over bare sand were greater at night than during the day, reflecting, in part, a tendency for species such as A. rueppellii to move into unvegetated areas to feed at night, when the likelihood of predation by visual predators would be reduced. Within Shark Bay, ichthyofaunal composition is influenced most by habitat type (vegetated v . unvegetated), followed in general by water depth and then region in the bay and time of year.     

Comparative predation rates on larval snappers (Lutjanidae) in oceanic, reef, and nearshore waters

The life cycle of most reef fishes involves pelagic larvae entering the nearshore environment to settle to benthic substrates. Settlement is considered to be highly risky as larvae encounter high rates of predation mortality associated with shallow nearshore habitats. This potential bottleneck may be particularly significant for many tropical snapper (Lutjanidae) species which bypass the reef to settle to very nearshore seagrass areas. To test the hypothesis that predation-related mortality increases as naïve late-stage fish larvae leave the offshore oceanic environment and enter the nearshore to settle, relative nocturnal predation rates on tethered late-stage snapper larvae were measured in oceanic, coral reef, and nearshore surface waters of the lower Florida Keys, USA. Both relative predation rate and probability of predation in oceanic areas seaward of the reef was significantly greater than over reef or nearshore seagrass/hardbottom habitats. This surprising result may be due to differences in the density or spatial distribution of potential predators between deep offshore (near flotsam at the surface) and shallow nearshore environments (demersal). These findings suggest that successful late-stage snapper larvae should avoid surface waters in deep oceanic areas and move upward in the water column as they pass over the reef and other shallow nearshore environments prior to settlement.     

What does body size mean,from the “plant's eye view”?

Alternative metrics exist for representing variation in plant body size, but the vast majority of previous research for herbaceous plants has focused on dry mass. Dry mass provides a reasonably accurate and easily measured estimate for comparing relative capacity to convert solar energy into stored carbon. However, from a “plant's eye view”, its experience of its local biotic environment of immediate neighbors (especially when crowded) may be more accurately represented by measures of “space occupancy” (S–O) recorded in situ—rather than dry mass measured after storage in a drying oven. This study investigated relationships between dry mass and alternative metrics of S–O body size for resident plants sampled from natural populations of herbaceous species found in Eastern Ontario. Plant height, maximum lateral canopy extent, and estimated canopy area and volume were recorded in situ (in the field)—and both fresh and dry mass were recorded in the laboratory—for 138 species ranging widely in body size and for 20 plants ranging widely in body size within each of 10 focal species. Dry mass and fresh mass were highly correlated (r² > .95) and isometric, suggesting that for some studies, between‐species (or between‐plant) variation in water content may be unimportant and fresh mass can therefore substitute for dry mass. However, several relationships between dry mass and other S–O body size metrics showed allometry—that is, plants with smaller S–O body size had disproportionately less dry mass. In other words, they have higher “body mass density” (BMD) — more dry mass per unit S–O body size. These results have practical importance for experimental design and methodology as well as implications for the interpretation of “reproductive economy”—the capacity to produce offspring at small body sizes—because fecundity and dry mass (produced in the same growing season) typically have a positive, isometric relationship. Accordingly, the allometry between dry mass and S–O body size reported here suggests that plants with smaller S–O body size—because of higher BMD—may produce fewer offspring, but less than proportionately so; in other words, they may produce more offspring per unit of body size space occupancy.     

1980—2007年大亚湾鱼类物种多样性、区系特征和数量变化

根据2004—2005年大亚湾海域底拖网鱼类调查数据,并结合1980—2007年的历史资料,分析了该海域鱼类的种类组成、区系特征、多样性、优势种和数量变化趋势.结果表明： 2004—2005年,大亚湾海域共记录鱼类107种,分属13目50科,以中下层鱼类的种类最多,为48种,其次是中上层和底层种类,分别为37种和21种.大亚湾鱼类区系具热带和亚热带特性,以暖水性种类占绝对优势,为97种,暖温性种类为10种.多样性指数以夏季最高（3.82）,其次是冬季（3.37）和秋季（3.00）,春季最低（2.40）.Pielou均匀度指数的季节变化情况与多样性指数相似.1980—2007年大亚湾海域鱼类群落特征发生了明显的变化：鱼类种类数减少,优势种更替明显.鱼类种类数由1980年的157种减少至1990年的110种,2004—2005年继续减少至107种;鱼类优势种由1980年以带鱼和银鲳等优质鱼为主,更替为以小型和低值的小沙丁鱼、小公鱼和二长棘鲷幼鱼为主.用包含年际变化趋势和季节性周期变化的回归模型模拟1980—2007大亚湾鱼类资源密度的变化,鱼类资源密度在1980—1999年和1990—2007年两个时期均呈下降趋势,但1990—2007年间下降幅度比1980—1999年间大;1980—1999年鱼类资源密度的季节波动幅度较平缓（振幅为0.099）,而1990—2007年的季节波动较大（振幅为0.420）,说明1990—2007年阶段大亚湾鱼类数量的季节变化更为显著.     

Composition and energy density of eggs from two species of freshwater turtle with twofold ranges in egg size

Lipid, protein, ash, carbohydrate and water content and energy density of eggs were measured from different clutches over a range of egg size in two species of freshwater turtle. Dry egg contents consisted of protein (54-60%), lipid (25-31%) and ash (5-6%) while carbohydrate was found to be negligible (<1%). Albumen consisted principally of water ( approximately 98%), and the dry component was composed of protein (47-51%), ash (19-26%) and lipid (18-21%), but contributed only a small amount ( approximately 2%) to overall dry egg contents. Energy density of dry albumen (15-17 kJ/g) was significantly lower than for dry yolk (26-27 kJ/g). Yolk consisted of 62-70% water, and the dry component was composed of protein (54-61%), lipid (25-31%) and ash (5-6%). Fractional concentrations of water, lipid, protein and ash and energy density remained constant over the range of egg size in Emydura signata eggs. In contrast, an increase in the yolk to albumen ratio and a decrease in water content of yolk as egg size increased caused the composition and energy density of Chelodina expansa eggs to vary systematically with egg size.     

Environmental influences on regulation of blood plasma/serum components in teleost fishes: a review

Concentrations of both inorganic and organic blood plasma/serum components of teleost fishes were reviewed in seven habitat/life-history categories. These were: freshwater; inland saline; estuarine and nearshore marine; pelagic and deep-sea; diadromous; southern cold-water; and northern cold-water. Plasma/serum osmolalities were compared among groups acclimated to/living in fresh and in salt water. Contributions of inorganic ions and colligative and non-colligative organic molecules were evaluated including with respect to melting and freezing points, and “antifreeze activity” of plasma/serum in species from cold marine waters. Possible roles of TMAO in deep-water fishes were reviewed. Discussion also included influences of ambient salinity and temperature on concentrations of plasma/serum components. Seasonal cycles of blood plasma/serum components were discussed, along with antifreeze concentrations in other body fluids and tissues of cold-water fishes. Regulatory patterns of plasma/serum osmolalities were compared among the most euryhaline of teleosts evaluated here. Highest mean values of plasma/serum osmolalities in sea water were seen in southern cold-water and in pelagic and deep-sea fishes. The southern cold-water group also had the lowest plasma/serum freezing points among these groups. Comparisons of mean plasma/serum Na⁺ and Cl⁻ concentrations among fishes from fresh waters did not differ significantly among groups, but species from cold marine waters showed higher levels than did other groups in marine waters. Plasma/serum osmotic, Na⁺ and Cl⁻ concentrations of these seven groups of teleosts were compared with those of other fish-like vertebrate groups. Possible impacts of global warming on regulatory responses of plasma/serum components were discussed.     

Parasites of coral reef fish larvae: its role in the pelagic larval stage

The pelagic larval stage is a critical component of the life cycle of most coral reef fishes, but the adaptive significance of this stage remains controversial. One hypothesis is that migrating through the pelagic environment reduces the risk a larval fish has of being parasitised. Most organisms interact with parasites, often with significant, detrimental consequences for the hosts. However, little is known about the parasites that larval fish have upon settlement, and the factors that affect the levels of parasitism. At settlement, coral reef fishes vary greatly in size and age (pelagic larval duration), which may influence the degree of parasitism. We identified and quantified the parasites of pre-settlement larvae from 44 species of coral reef fishes from the Great Barrier Reef and explored their relationship with host size and age at settlement, and phylogeny. Overall, less than 50% of the larval fishes were infected with parasites, and over 99% of these were endoparasites. A Bayesian phylogenetic regression was used to analyse host-parasite (presence and intensity) associations. The analysis showed parasite presence was not significantly related to fish size, and parasite intensity was not significantly related to fish age. A phylogenetic signal was detected for both parasite presence and intensity, indicating that, overall, closely related fish species were likely to have more similar susceptibility to parasites and similar levels of parasitism when compared to more distantly related species. The low prevalence of infection with any parasite type and the striking rarity of ectoparasites is consistent with the ‘parasite avoidance hypothesis’, which proposes that the pelagic phase of coral reef fishes results in reduced levels of parasitism.

     

Patterns of diversity, depth range and body size among pelagic fishes along a gradient of depth

Studies of geographical patterns of diversity have focused largely on compiling and analysing data to evaluate alternative hypotheses for the near‐universal decrease in species richness from the equator to the poles. Valuable insights into the mechanisms that promote diversity can come from studies of other patterns, such as variation in species distributions with elevation in terrestrial systems or with depth in marine systems. To obtain such insights, we analysed and interpreted data on species diversity, depth of occurrence and body size of pelagic fishes along an oceanic depth gradient. We used a database on pelagic marine fishes native to the north‐east Pacific Ocean between 40°N and 50°N. We used data from the Pacific Rim Fisheries Program that were obtained from commercial, management and scientific surveys between 1999 and 2000. Depth of occurrence and maximum body length were used to assess the distributions of 409 species of pelagic fishes along a depth gradient from 0 to 8000 m. A presence–absence matrix was used to classify the depth range of each species into 100‐m intervals. Atmar & Patterson's (1995 ) software was used to quantify the degree of nestedness of species distributions. Pelagic fish species diversity decreased steeply with increasing depth; diversity peaked at less than 200 m and more than half of the species had mean depths of occurrence between 0 and 300 m. The distribution of species showed a very strong nested subset pattern along the depth gradient. Whereas species with narrow ranges were generally restricted to shallow waters, wide‐ranging species occurred from near the surface to great depths. The relationship between maximum body size and mean depth range differed between teleost and elasmobranch fishes: being positive for teleosts, but negative for elasmobranches. Results support hypotheses that some combination of high productivity and warm temperature promote high species diversity, and reject those that would attribute the pattern of species richness to the mid‐domain effect, habitat area, or environmental constancy. The data provided a clear example of Rapoport's rule, a negative correlation between average depth range and species diversity.     

Proximate composition and energy density of nototheniid and myctophid fish in McMurdo Sound and the Ross Sea,Antarctica

Nototheniid and myctophid fish are primary prey for marine piscivores, yet little is known about their nutritional value. In this study, we characterized the proximate composition [PC: water, fat (neutral lipids), crude protein (CP) and ash] and energy density (ED; kJ g⁻¹) of fifteen fish species from McMurdo Sound and the Ross Sea, Antarctica. We assayed the entire fish for all species except for the large Antarctic toothfish, Dissostichus mawsoni (muscle tissue only). On a wet mass basis (WM), fish were variable in composition: moisture content ranged from 64.9 to 87.3% WM, fat from 0.5 to 17.4% WM, CP from 7.7 to 16.7% WM, ash from 11.2 to 21.0% FFDM (fat-free dry mass), and ED from 2.9 to 10.3 kJ g⁻¹. Myctophids and pelagic nototheniids such as Pleuragramma antarcticum and D. mawsoni were high in fat content (7–17% WM), while a bathylagid and benthic nototheniids including most Trematomus spp. and Lepidonotothen squamifrons were low in fat (0.5–4% WM). The epibenthic Trematomus species (T. eulepidotus and T. lepidorhinus) were intermediate. Energy density tracked fat content, with highest values in myctophids and pelagic nototheniids. The variation in nutrient and energy density confirms that prey composition must be taken into account when modelling energy and nutrient fluxes within the Antarctic ecosystem. Further analyses of prey collected over a number of different locations and seasons are needed in order to determine how the nutritional value of certain species might affect annual or decadal variation in reproductive success or population size of top predators.     

Recruitment dynamics and fishery characteristics of juvenile goatfishes Mulloidichthys spp. in Hawai‘i

The most common goatfishes in Hawai‘i, Mulloidichthys flavolineatus and M. vanicolensis, comprise a unique resource due to their cultural, ecological and biological significance. These species exhibit pulse-type recruitment to nearshore areas during the summer months. Such pulses of juvenile fishes provide prey for pelagic and nearshore fishes and support a popular directed fishery. However, limited scientific information exists on juvenile stages of these fishes, known locally as oama, despite their contribution to coastal ecology and the extensive nearshore fisheries. Here we resolve growth rates, habitat preferences, hatching dates, size and age structure, as well as fishing catch rates based on new recruits in 2014 and 2015. We sampled 257 M. flavolineatus and 204 M. vanicolensis to compare ecological and fisheries characteristics between species and years. Both show strong habitat segregation, with M. vanicolensis found almost exclusively on hard and M. flavolineatus on soft substrates. Oama recruited in anomalously high numbers in 2014, a trend reflected in a higher catch per unit effort. In contrast, 2015 recruits grew faster, were heavier on average and hatched later than during 2014. Both species have calculated hatch dates in March to July, with M. vanicolensis hatching earlier, recruiting earlier and being consistently larger than M. flavolineatus. This baseline information regarding recruitment and early life-history characteristics can enhance management for other data-limited species that comprise a substantial component of nearshore fisheries in Hawai‘i.     

Relationship between pelagic larval duration and abundance of tropical fishes on temperate coasts of Japan

The influence of pelagic larval duration (PLD) and egg type dispersal capabilities of 35 demersal and pelagic-spawning tropical fish species is examined in relation to their abundance on the temperate coasts of Japan. The PLDs of pelagic spawners were significantly longer than those of demersal spawners, and a high occurrence of pelagic spawners on the temperate coasts suggests that these fishes are more easily transported to temperate coasts than demersal spawners. For demersal spawners, the common species on the temperate coasts had significantly longer PLDs than the rare species; this suggests that PLD is a major factor influencing the distribution patterns of tropical demersal spawners on temperate coasts. Moreover, a negative correlation between PLD and the abundance of some species of pelagic and demersal spawners suggests the presence of reproductively active fishes in northern subtropical and even in temperate waters.     

Lipid content in the early life stages of three mesopelagic fishes

Changes in lipid concentration during early ontogenetic stages were determined in three mesopelagic fish species, Benthosema glaciale , Hygophum benoiti and Maurolicus muelleri . Total lipid content per larva was related to size and mass and increased over the course of development. In all three species, the dry mass : total lipid ratio displayed a better fit than the standard length : total lipid ratio. Larvae of B. glaciale had a higher amount of lipid content, at a given mass, than the other two species. The rate of lipid accumulation with increasing larval development was similar in B. glaciale and H. benoiti , and both were higher than in M. muelleri larvae. Furthermore, total lipid concentration values, as a proportion of dry mass, increased significantly from the larval to the juvenile stages in B. glaciale (from 16 to 55%) and M. muelleri (from 9 to 20%). The present study has allowed comparisons to be drawn of the ability on the early developmental stages of deep‐sea fishes to accumulate energy reserves, both within and among species.     

The trophic ecology of Atlantic cod: insights from tri-monthly, localized scales of sampling

The meso-scale trophic dynamics of cod Gadus morhua were examined based upon tri-monthly stomach sample collections from a nearshore, localized ( c. 800 km²) region off Cape Cod, Massachusetts, U.S.A. The major objective for this work was to relate any changes in cod diet and amount of food eaten to seasonal variations in prey availability, water temperature and spawning at a spatial scale between broad-scale and laboratory studies. Results suggested that the type and amount of food eaten by cod was generally consistent throughout a year and repeatable across years. Cod feeding was marked by two periods of increased feeding, corresponding to the arrival of small pelagic fishes in the area. This pelagic migration and subsequent increased feeding by cod occurred during important periods in the life history of cod ( e.g . spawning and overwintering). Similar annual patterns in food consumption and diet composition were remarkably consistent over the 2·5 years of the project, suggesting important feeding periods for cod that correspond to environmental and biological events. The diet of cod was composed primarily of several species of forage fishes [ e.g. herrings (predominantly Atlantic herring Clupea harengus ), sand lance Ammodytes sp. and Atlantic mackerel Scomber scombrus ], ophiuroids, Cancer sp. crabs and other small crustaceans. It was inferred that cod exhibited a maintenance diet on local forage fishes and benthic macroinvertebrates, augmenting their diet by seasonally gorge feeding upon migrating pelagic species.     

Diet and feeding niches of juvenile Gadus morhua, Melanogrammus aeglefinus and Merlangius merlangus during the settlement transition in the northern North Sea

A study on the feeding ecology of juvenile cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus during the pelagic to demersal transition was carried out on fishes sampled throughout their settlement season at a local nursery ground in the north-western North Sea, off the Scottish east coast. A comprehensive quantitative taxonomic analysis of the diets, as described in the paper, showed the emergence of distinctive feeding niches, minimizing the potential for competition between species and size categories. The diet of the juveniles changed with fish size, water depth, time of year and distance offshore. Small G. morhua were present in the study area earlier in the season, settled further inshore and ate a higher proportion of pelagic prey (copepods) and as size increased they moved into deeper waters and targeted larger, more benthic prey. As M. aeglefinus grew larger and moved into deeper waters, a diet of largely copepods, amphipods, pelagic Ammodytes spp., cyprids and pelagic gastropods evolved to one dominated predominantly by fishes and benthic invertebrates. In the case of M. merlangus, widespread ages and sizes throughout the sampling season, a consequence of their more protracted spawning season, resulted in dietary changes which were more likely to be influenced by seasonal changes in the prey field, in addition to developmental (size) changes, than the diets of the other two species.     

Auditory sensitivity in settlement-stage larvae of coral reef fishes

The larval phase of most species of coral reef fishes is spent away from the reef in the pelagic environment. At the time of settlement, these larvae need to locate a reef, and recent research indicates that sound emanating from reefs may act as a cue to guide them. Here, the auditory abilities of settlement-stage larvae of four species of coral reef fishes (families Pomacentridae, Lutjanidae and Serranidae) and similar-sized individuals of two pelagic species (Carangidae) were tested using an electrophysiological technique, auditory brainstem response (ABR). Five of the six species heard frequencies in the 100–2,000 Hz range, whilst one carangid species did not detect frequencies higher than 800 Hz. The audiograms of the six species were of similar shape, with best hearing at lower frequencies between 100 and 300 Hz. Strong within-species differences were found in hearing sensitivity both among the coral reef species and among the pelagic species. Larvae of the coral reef species had significantly more sensitive hearing than the larvae of the pelagic species. The results suggest that settlement-stage larval reef fishes may be able to detect reef sounds at distances of a few 100 m. If true hearing thresholds are lower than ABR estimates, as indicated in some comparisons of ABR and behavioural methods, the detection distances would be much larger.     

Biology of the small pelagic fishes in the New Volta Lake in Ghana. Part III: Sex and reproduction

Reproductive patterns of five species, from three families, of small pelagic fishes in the new Volta Lake in Ghana showed several similar features. These included sex size defferences, males maturing and reaching final sizes smaller than females; heterogenous sex ratios in four species, being most markedly unequal usually at peak breeding times; demersal eggs; and extended fractional spawning patterns. The clupeids Pellonula and Cynothrissa and the cyprinid Barilius all breed in the dry season, whereas the schilbeids Physailia and Siluranodon are wet-season spawners. Only Pellonula and Physailia have extended their breeding season in the new lake to cover most of the year; the other species have not, although Siluranodon spawns into the early dry season. In the lake environment Pellonula's pelagic larva is no longer endangered by seasonal floods, whereas Physailia can use the lake's continuous “high waters” for extended breeding. Relaxation of breeding patterns and protracted fractional spawning has allowed best exploitation of the new regime.     

Feeding habits and gill raker morphology of three planktivorous pelagic fish species off the coast of northern and western Kyushu in summer

Feeding habits and gill raker morphology were examined for the three major planktivorous pelagic fishes, Japanese anchovy Engraulis japonicus , Pacific round herring Etrumeus teres and Japanese jack mackerel Trachurus japonicus , off the northern and western coasts of Kyushu, in the north‐eastern part of the East China Sea in the summer months of 2001. Using fishes in the same size range (80–140 mm, standard length), the stomach contents of the three fish species were compared. The diet of the Japanese anchovy mainly consisted of Oncaeidae copepods, while the diets of the Pacific round herring and Japanese jack mackerel were dominated by calanoid copepods at all stations. Comparisons between prey size in the stomach, zooplankton size in the water and gill raker morphology suggested that the stomach contents of the three species were characterized mainly by the difference in the feeding behaviour between Japanese anchovy (filter‐feeding) and the other two species (particulate‐feeding), rather than by the difference in the morphology of feeding apparatus only. It was concluded that behavioural adaptations in the feeding of these pelagic fishes brought about trophic partitioning to some degree in this pelagic ecosystem in summer. Although the diets of these three species overlapped to some extent, there was still little likelihood of competition between the Japanese anchovy and the other two species. The potential for competition between the Pacific round herring and the Japanese jack mackerel is discussed.