Seasonal patterns in feeding ecology of three small fishes in the Biandantang Lake, China

Feeding ecology of three small fish species, Hypseleotris swinhonis, Ctenogobius giurinus and Pseudorasbora parva was studied seasonally in the Biandantang Lake, a small, shallow lake in central China. Gut length, adjusted for total body length, was significantly higher in spring than in other seasons for all the three species. Seasonal changes in gut length were not associated with changes in food quality. Weight of fore-gut contents, adjusted for body weight, was significantly higher in winter and spring than in summer and autumn in H. swinhonis and C. giurinus , and significantly higher in autumn than in spring and summer for P. parva. Percentage of empty fore-guts was highest in summer and lowest in spring for H. swinhonis and C. giurinus , and highest in winter and lowest in autumn for P. parva. Diet of the three small fishes showed apparent seasonal changes, and these changes reflected partly the seasonal fluctuations of food resources in environment. Diet breadth was high in winter and low in autumn for H. swinhonis , high in winter and low in spring and summer for C. giurinus , and high in autumn and low in spring for P. parva. Diet overlaps between pairs of species were biologically significant in most cases, except between H. swinhonis and P. parva in summer and autumn and between C. giurinus and P. parva in autumn.     

Differences in gill raker morphology between two local populations of a benthophagous filter-feeding fish, Goniistius zonatus (Cheilodactylidae)

Gill raker morphology of a benthophagous fish Goniistius zonatus (Cheilodactylidae) (10.9–29.2 cm SL), using a filter-feeding mode, was compared between two locations (Morode and Arakashi) in southern Japan. Although gill raker number and gill raker length at the two locations did not differ, gill raker spacing was narrower relative to overall fish size at Morode than at Arakashi, mainly because gill raker width was greater at Morode. The difference of gill raker spacing is unlikely to have a genetic or physiochemical explanation. Small invertebrates (≤1.0 mm) were dominant on the substrate at Morode but were less common at Arakashi. Such small animals were consumed by many fish at Morode but were rarely exploited at Arakashi. At Morode, the narrow gill raker spacing would be effective in retaining small prey, which should be an important energy resource in this population. The difference of interraker spacing at the two locations seems to be related to available prey size at each location. Received: November 14, 2000 / Revised: February 13, 2001 / Accepted: February 28, 2001     

Gill raker structure and selective predation on zooplankton by particulate feeding fish

The relationship between the gill raker structure of planktivorous fish (number, distance between gill rakers and length) and selective feeding on different species and size classes of zooplankton was studied. Gill raker structure was measured for brown trout Salmo trutta , Arctic charr Salvelinus alpinus , whitefish Coregonus lavaretus , roach Rutilus rutilus , bleak Alburnus alburnus , and three-spined stickleback Gasterosteus aculeatus . All species are facultative planktivorous fish and occur commonly in Scandinavian lakes. The effect of gill raker structure was studied by comparing prey found in fish stomachs with the availability of zooplankton from several lakes. Gill raker length and distance were significantly correlated with fish length. Although gill raker structure differed among species, all fish species selected the larger zooplankters. The minimum size of cladoceran species found in fish stomachs was much smaller than the distance between gill rakers. Despite great differences in gill raker spacing, the minimum size ingested of Daphnia galeata and Bosmina longispina was similar for all predators. The hypothesis that small zooplankton are strained and retained by the gill rakers in particulate feeding planktivorous fish, particularly in salmonids and roach, is rejected.     

Trophic ecology and gill raker morphology of seven catostomid species in Iowa rivers

Understanding the trophic ecology of closely‐related species is important for providing insight on inter‐specific competition and resource partitioning. Although catostomids often dominate fish assemblages in lotic systems, little research has been conducted on their ecology. This study was developed to provide information on the trophic ecology of catostomids in several Iowa rivers. Food habits, diet overlap, and gill raker morphology were examined for highfin carpsucker Carpiodes velifer, quillback C. cyprinus, river carpsucker C. carpio, golden redhorse Moxostoma erythrurum, shorthead redhorse M. macrolepidotum, silver redhorse M. anisurum, and northern hogsucker Hypentelium nigricans sampled from four Iowa rivers (2009). Diet overlap among all species was calculated with Morista’s index (C). Food habit niche width was quantified with Levin’s index (B) and similarity in gill raker morphology was compared with analysis of covariance. Values from Morista’s index suggested significant overlap in the diets of highfin carpsucker and river carpsucker (C = 0.81), quillback and river carpsucker (C = 0.66), and shorthead redhorse and silver redhorse (C = 0.67). Levin’s index indicated that golden redhorse (B = 0.32), quillback (B = 0.53), and river carpsucker (B = 0.41) had the most generalized feeding strategies as their food niche widths were substantially wider than the other species. Gill raker length and spacing were positively correlated with the standard length of the fish for all species (gill raker length: r² = 0.67–0.88, P ≤ 0.01; gill raker spacing: r² = 0.63–0.73, P ≤ 0.01). Slopes of regression of gill raker length and spacing to standard lengths were significantly (P ≤ 0.05) different among species, indicating that rates of change in gill raker morphology with body length varied among species. Differences in gill raker morphology likely allow catostomids to partition resources and reduce competitive interactions.     

Food selection and growth of young snakehead Channa striatus

Food selection and growth of young snakehead Channa striatus were studied in the laboratory and in a field trial. In the laboratory, first-feeding snakehead larvae of 6–7 mm total length (TL) with a mouth opening of 0.55 mm selected for Artemia nauplii, and against formulated feed. Fish began feeding on formulated feed at 12mm TL when their mouth width reached 1.0mm. In both laboratory and field trials, snakehead diets changed as fish size increased. For fish 15–20 mm TL, cladocerans and copepods were 96.5% of their diet. With fish 30–40 mm TL, zooplankton consumption was greatly reduced while benthic organism consumption increased. Fish 45–50 mm TL fed exclusively on benthic invertebrates. Diet shift from zoo-plankton to benthic invertebrates was not due to reduced zoo-plankton availability, but was instead related to changes in gill raker structure. Low density of benthic invertebrates in the field trial caused reduced fish growth rates when fish switched diets from zooplankton to benthos. Our results indicate that snake-head can take Artemia nauplii as a larval starter food, then accept formulated feed at ≥12 mm TL. Zooplankton can serve as food for snakehead < 40 mm, but formulated feed should be provided for larger fish which are unable to catch zoo-plankton.     

The foraging ecology of two pairs of congeneric demersal fish species: importance of morphological characteristics in prey selection

The feeding habits of two sympatric species pairs of demersal fish ( Mullus barbatus-Mullus surmuletus, Serranus cabrilla-Serranus hepatus ) which occupy the shallow coastal area (25–30 m) in Iraklion Bay were investigated from samples collected on a monthly basis (August 1990 to August 1992). Stomach content analyses revealed that all of them were carnivores, feeding mainly on benthic invertebrates, and that each species consumed a narrow range of prey species with no significant dietary overlap. The morphology of their feeding apparatus was compared to examine the effect of any morphological differences on food selection and resource partitioning between the fish species. The species could be distinguished on the basis of the size of their mouth gape, the number of gill rakers and the length of their intestine. This study shows that each species pair follows a different strategy segregating along food niche dimensions. In particular, M. barbatus and M. surmuletus segregate their feeding niche consuming different prey taxa with similar sizes whereas S. cabrilla and S. hepatus differ considerably with respect to the degree to which prey species contribute to their diets coupled with differences in mean prey sizes.     

Diet reveals links between morphology and foraging in a cryptic temperate reef fish

Predators select prey so as to maximize energy and minimize manipulation time. In order to reduce prey detection and handling time, individuals must actively select their foraging space (microhabitat) and populations exhibit morphologies that are best suited for capturing locally available prey. We explored how variation in diet correlates with habitat type, and how these factors influence key morphological structures (mouth gape, eye diameter, fin length, fin area, and pectoral fin ratio) in a common microcarnivorous cryptic reef fish species, the triplefin Helcogrammoides cunninghami. In a mensurative experiment carried out at six kelp‐dominated sites, we observed considerable differences in diet along 400 km of the Chilean coast coincident with variation in habitat availability and prey distributions. Triplefins preferred a single prey type (bivalves or barnacles) at northern sites, coincident with a low diversity of foraging habitats. In contrast, southern sites presented varied and heterogeneous habitats, where triplefin diets were more diverse and included amphipods, decapods, and cumaceans. Allometry‐corrected results indicated that some morphological structures were consistently correlated with different prey items. Specifically, large mouth gape was associated with the capture of highly mobile prey such as decapods, while small mouth gape was more associated with cumaceans and copepods. In contrast, triplefins that capture sessile prey such as hydroids tend to have larger eyes. Therefore, morphological structures co‐vary with habitat selection and prey usage in this species. Our study shows how an abundant generalist reef fish exhibits variable feeding morphologies in response to the distribution of potential habitats and prey throughout its range.     

Feeding ecology of larval and juvenile black seabream (Acanthopagrus schlegeli) and Japanese seaperch (Lateolabrax japonicus) in Tolo Harbour, Hong Kong

Black seabream, Acanthopagrus schlegeli, and Japanese seaperch, Lateolabrax japonicus, are important commercial species in the coastal waters of western Pacific Ocean, including Japan, Korea and China. In Hong Kong, larvae and juveniles of these two species occur in bays and estuaries during late winter and spring. This study reports on the ontogenetic changes in food habits in larvae and juveniles of these species in an artificial rocky shore area. Copepods and cladocerans were the most numerous food items for black seabream. There was a shift to larger and benthic prey as the fishes grew. Japanese seaperch <2.1cm fed predominantly on copepods and cladocerans, while larger prey were added as fish size increased. Japanese seaperch >6.0cm were piscivorous. Maximum prey width increased with fish standard length and mouth gape width in both species. Overall, black seabream showed greater diet breadth than did Japanese seaperch. In black seabream, diet breadth increased with fish size. In Japanese seaperch, diet breadth increased with size for fishes <4.0cm, then decreased as the fishes became piscivorous. Prey selectivity in black seabream was determined using information on prey availability in plankton samples. In general, preference was stronger for cypris larvae, Penilia avirostris and decapod larvae than for copepods and podonids. In recent years, overfishing and environmental degradation have led to the decline of fish populations in Tolo Harbour. Absence of fishes with empty gut indicates that inner Tolo Harbour is still an important nursery area for these two commercial species.     

Abrupt changes in defence and trophic morphology of the giant threespine stickleback (Gasterosteus sp.) following colonization of a vacant habitat

To evaluate the first stages of adaptation and differentiation following colonization into a vacant and ecologically divergent habitat, 100 melanistic and low‐plated adult threespine stickleback (Gasterosteus aculeatus) exhibiting gigantism in body size and robust spines were transferred in 1993 from a large dystrophic lake (Mayer Lake, Haida Gwaii, British Columbia, Canada) with a diverse vertebrate predator regime, into an adjacent fishless eutrophic pond with macroinvertebrate piscivores. Eight generations were examined as a test of multiple functional hypotheses on the morphological traits that differentiate lake and pond stickleback throughout their distribution. Measurements of 20 defence and trophic traits were made on 275 wild‐caught fish collected from the source and transplant populations over multiple years. There have been significant reductions (males: females) in plate count (8%: 0.5%), lateral plate 2 frequency (46%: 17%), lateral plate 3 height (17%: 18%), pelvic spine length (12%: 6%), dorsal spine length (21%: 16%), gill raker number (5%: 1%), and gill raker length (37%: 43%), and an increase in gill raker spacing (+5%: 0%), jaw length (+5%: +4%), and eye diameter (+8%: +7%). These changes within eight generations represent one‐third of the morphological differences observed between naturally established large lake and pond populations in these archipelago and are all in the direction predicted from the change in habitat. Field samples indicate strong selection in the colonists although lab‐reared individuals implicate an additional role of plasticity for dorsal spine and gill raker lengths, which may contribute to the rapid adaptation into novel and highly divergent selective landscapes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 494–509.     

西藏拉鲁湿地和茶巴朗湿地外来鱼类群落结构及变动趋势

研究于2019—2021年在西藏拉鲁湿地和茶巴朗湿地使用刺网和地笼等组合渔具开展了鱼类实地调查, 分析了外来鱼类物种组成、优势种和群落功能多样性, 并结合已发表的文献资料, 探讨了西藏湿地外来鱼类群落结构的变动趋势及影响。结果表明, 共采集到外来鱼类10种, 隶属于4目5科, 包括鲫(Carassius auratus)、麦穗鱼(Pseudorasbora parva)、鲤(Cyprinus carpio)、丁鱥(Tinca tinca)、棒花鱼(Abbottina rivularis)、泥鳅(Misgurnus anguillicaudatus)、大鳞副泥鳅(Paramisgurnus dabryanus)、鲇(Silurus asotus)、小黄?(Micropercops swinhonis)和中华青鳉(Oryzias sinensis)。外来鱼类的个体数和重量分别占本地种和外来种总渔获物的94.86%和70.71%, 其中主要组成为鲫和麦穗鱼等小型鱼类。相对重要性指数(IRI)表明鲫、麦穗鱼、大鳞副泥鳅和鲤4种为拉鲁湿地外来鱼类优势物种, 鲫、麦穗鱼和小黄?3种为茶巴朗湿地的优势物种。在拉鲁湿地和茶巴朗湿地鱼类种类组成、个体数量和生物量中外来鱼类均已占据优势地位, 且外来鱼类的群落功能多样性(FD)亦高于土著鱼类。结合历史数据, 西藏拉鲁湿地和茶巴朗湿地已记录外来鱼类12种, 其中具高度入侵风险物种达6种, 外来鱼类物种数从2000年左右的2种增加到现在的10种, 且丁鱥和中华青鳉分别在西藏自然水体中和茶巴朗湿地中首次被发现。此外, 两个湿地12种外来鱼类均为拉萨市场中的常见经济鱼类及携带鱼类, 是由于放生而进入湿地自然水体中, 且鲫、大鳞副泥鳅和麦穗鱼等均已建立自然种群。因此, 加强对放生的科学管理及开展外来鱼类的长期监测, 是防范外来鱼类入侵及高原湿地生物多样性保护的迫切任务。     

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.     

Comparative digestive biology between the ponyfishes from the Pranburi River estuary,Thailand

We investigated the digestive biology of two prevalent leiognathid species in Pranburi River estuary, Thailand: the decorated ponyfish (Nuchequula gerreoides) and the splendid polyfish (Eubleekeria splendens). A total of 632 samples collected from February to April and September to November 2017 were analysed using morphological and histological approaches. The overall structures were similar between the species: a short mucous-cell-rich oesophagus region, a well-developed gastric gland uniformly present across the stomach's mucosal layer, and three finger-like pyloric caeca between the stomach and intestine. However, there were marked differences in the mouth, gill raker, and intestinal coefficient (IC). N. gerreoides had a relatively longer mouth, smoother gill rakers, and an IC of 1.08 ± 0.01, similar to those of other carnivorous fish. In contrast, the gill raker of E. splendens had more villiform teeth that can filter-feed better, and their IC was 2.16 ± 0.02 (i.e., longer intestine). Although digestive structures were generally similar between the ponyfishes, these differences suggest that N. gerreoides is relatively carnivorous with stronger suction, whereas E. splendens may be an omnivorous or herbivorous filter-feeder.     

Diel food selection of pelagic Arctic charr, Salvelinus alpinus (L.), and brown trout, Salmo trutta L., in Lake Atnsjø, SE Norway

Patterns of diel food selection in pelagic Arctic charr, Salvelinus alpinus (L.) and brown trout, Salmo trutta L. were investigated in Lake Atnsjo, SE Norway, by gillnet sampling during July-September 1985. Arctic charr feed almost exclusively on zooplankton both day and night, while brown trout had a diurnal shift in diet. For this species zooplankton made up a considerable part of the diet in the daytime, while at night the diet consisted mainly of surface insect and chironomid pupae. Both species had a selective feeding mode on zooplankton during the day and night. Arctic charr had a higher gill raker number and a denser gill raker spacing compared with brown trout. Still, the differences in prey size between the two species were small. We argue that the observed differences in food selection between Arctic charr and brown trout can be explained by differing abilities to detect food items under low light conditions.     

Influence of environmental factors and individual traits on the diet of non-native hybrid bigheaded carp (Hypophthalmichthys molitrix × H. nobilis) in Lake Balaton,Hungary

Planktivorous silver carp and bighead carp (collectively, the bigheaded carps) have been stocked worldwide and their invasion has caused severe impacts on many freshwater ecosystems. Exploiting the chance provided by the specific hybrid bigheaded carp stock in Lake Balaton (Hungary) covering the entire morphological range between the two species (including gill raker morphology), we implemented a comprehensive study (1) to reveal the feeding habits of hybrid bigheaded carps living in a mesotrophic, lacustrine habitat and (2) to assess how biotic and abiotic environmental factors and gill raker morphology affect diet composition. We found that all bigheaded carps utilized primarily zooplankton and neglected the scarce and inefficiently digestible phytoplankton, irrespective of gill raker morphology. Moreover, we observed strikingly high levels of inorganic debris consumption, but the proportion of inorganic matter in the guts was not associated directly with the concentration of suspended inorganic particles. Variance in the diet composition of bigheaded carps was related mostly to environmental factors, including the wind-induced resuspension of inorganic particles and seasonally variable availability of food resources. In conclusion, the effects of abiotic environmental factors and available food resources could overwhelm the effect of gill raker morphology in shaping the feeding habits of bigheaded carps.

     

Experimental evidence for trait utility of gill raker number in adaptive radiation of a north temperate fish

North temperate fish in post‐glacial lakes are textbook examples for rapid parallel adaptive radiation into multiple trophic specialists within individual lakes. Speciation repeatedly proceeded along the benthic–limnetic habitat axis, and benthic–limnetic sister species diverge in the number of gill rakers. Yet, the utility of different numbers of gill rakers for consuming benthic vs. limnetic food has only very rarely been experimentally demonstrated. We bred and raised families of a benthic–limnetic species pair of whitefish under common garden conditions to test whether these species (i) show heritable differentiation in feeding efficiency on zooplankton, and (ii) whether variation in feeding efficiency is predicted by variation in gill raker numbers. We used zooplankton of three different size classes to investigate prey size dependency of divergence in feeding efficiency and to investigate the effect strength of variation in the number of gill rakers. Our results show strong interspecific differences in feeding efficiency. These differences are largest when fish were tested with the smallest zooplankton. Importantly, feeding efficiency is significantly positively correlated with the number of gill rakers when using small zooplankton, also when species identity is statistically controlled for. Our results support the hypothesis that a larger number of gill rakers are of adaptive significance for feeding on zooplankton and provide one of the first experimental demonstrations of trait utility of gill raker number when fish feed on zooplankton. These results are consistent with the suggested importance of divergent selection driven feeding adaptation during adaptive radiation of fish in post‐glacial lakes.     

Adaptive divergence between lake and stream populations of an East African cichlid fish

Divergent natural selection acting in different habitats may build up barriers to gene flow and initiate speciation. This speciation continuum can range from weak or no divergence to strong genetic differentiation between populations. Here, we focus on the early phases of adaptive divergence in the East African cichlid fish Astatotilapia burtoni, which occurs in both Lake Tanganyika (LT) and inflowing rivers. We first assessed the population structure and morphological differences in A. burtoni from southern LT. We then focused on four lake–stream systems and quantified body shape, ecologically relevant traits (gill raker and lower pharyngeal jaw) as well as stomach contents. Our study revealed the presence of several divergent lake–stream populations that rest at different stages of the speciation continuum, but show the same morphological and ecological trajectories along the lake–stream gradient. Lake fish have higher bodies, a more superior mouth position, longer gill rakers and more slender pharyngeal jaws, and they show a plant/algae and zooplankton‐biased diet, whereas stream fish feed more on snails, insects and plant seeds. A test for reproductive isolation between closely related lake and stream populations did not detect population‐assortative mating. Analyses of F1 offspring reared under common garden conditions indicate that the detected differences in body shape and gill raker length do not constitute pure plastic responses to different environmental conditions, but also have a genetic basis. Taken together, the A. burtoni lake–stream system constitutes a new model to study the factors that enhance and constrain progress towards speciation in cichlid fishes.     

Genetic differentiation in gill raker number and length in sympatric anadromous and nonanadromous morphs of sockeye salmon, Oncorhynchus nerka

The genetic and environmental basis for polymorphism in gill raker number and length in sympatric anadromous and nonanadromous morphs of sockeye salmon, Oncorhynchus nerka, was investigated. Analysis of 30 full sib families involving pure types and reciprocal hybrids revealed that the variation was partitioned significantly among families within cross types and among cross types in both traits. As in the wild, kokanee displayed more gill rakers than sockeye; reciprocal hybrids displayed intermediate counts. Gill raker length also varied markedly among cross types, with pure sockeye displaying 19% longer gill rakers than comparable sized kokanee. This difference was in the opposite direction predicted, given the common positive association between gill raker number and length in sympatric morphs of the same species in fishes. Gill raker number and length were generally not correlated within cross types, suggesting independent divergence of the traits. The results are discussed in relation to genetic and trophic divergence of the morphs and to factors selecting for differentiation in the two gill raker traits.     

Morphological limitations, prey size selectivity, and growth response of juvenile atlantic salmon, Salmo salar

The head and jaw movements involved in capture, buccal manipulation, ingestion and rejection of prey were investigated using sequential photography of juvenile Atlantic salmon feeding in a simulated stream environment. The results are described and discussed and mouth breadth and gill raker spacing are proposed as morphometric limitations to the range of prey sizes available which remains constant at 0·06 · fish fork length ( PFR ).
A recirculatory flume tank was used to study prey size selectivity behavior. Simplified downstream-drifting prey items elicited a variety of responses depending on their physical size. One hundred percent of offered prey of PFR 0·025 were ingested, while 90 % of prey at PFR 0·051 and 100% of prey at PFR 0·105 were rejected. It is demonstrated that fish show negative selection for prey sizes smaller than PFR 0·025 and that prey of this size elicits maximum growth response.
The validity of the proposed morphometric limitations on the available prey sizes is demonstrated by reference to selectivity behaviour and prey size related differential growth.     

Trophic polymorphism, habitat and diet segregation in Percichthys trucha (Pisces: Percichthyidae) in the Andes

Divergent natural selection affecting specific trait combinations that lead to greater efficiency in resource exploitation is believed to be a major mechanism leading to trophic polymorphism and adaptive radiation. We present evidence of trophic polymorphism involving two benthic morphs within Percichthys trucha , a fish endemic to temperate South America. In a series of lakes located in the southern Andes, we found two morphs of P. trucha that could be distinguished on the basis of gill raker length and five other morphological measures, most of which are likely associated with the use of food resources. The differences were consistent across all lakes examined, and were correlated with habitat use and diet. Individuals with longer gill rakers were more abundant in the littoral zone (littoral morph) while the short gill-raker morph was more abundant at 10 m depth and deeper (deep benthic morph). Both morphs fed primarily on benthic invertebrates, but the littoral morph fed more on larval Anisoptera than did the deep benthic morph. Phenotypic correlations among traits were high for the littoral morph, but low and non-significant for the deep-benthic morph. We suggest that gill raker length may influence the relative efficiency of suction feeding for the two morphs. This is the first evidence of trophic polymorphism in fishes from temperate South America.     

三峡库区丰都江段鱼类早期资源现状

2014 年47 月鱼类主要繁殖季节于三峡库区(重庆丰都县)进行鱼类早期资源调查, 以了解三峡库区鱼类早期资源现状, 四大家鱼在库区是否仍有产卵场等问题。调查共采集到鱼类50 种, 分属5 目9 科。采集时, 卵汛出现在6 月后流速较高的时段, 其中贝氏的数量最多, 占86.24%。仔鱼出现的高峰期为6 月上旬至7 月中旬, 太湖新银鱼的数量最多, 占58.36%, 其次为子陵吻虎鱼, 占27.04%。在仔鱼中, 种类组成呈明显的月份差异, 4 月鲤、鲫占数量优势;5 月太湖新银鱼、子陵吻 虎鱼占数量优势;6 月后鲌亚科、鳅科、鳜等种类开始出现, 种类明显增多。通过估算, 调查期间流经丰都断面的鱼卵总量为4.37108 粒, 四大家鱼鱼卵为0.21107 粒;仔鱼总量为111.98108 尾, 四大家鱼仔鱼为0.21108 尾。通过产卵场的推算, 丰都断面采集的四大家鱼来自涪陵城区江段和三峡库区上游的重庆巴南区至朱沱镇江段的产卵场。通过对卵苗漂流密度的昼夜规律分析, 6 月之前夜间仔鱼密度显著高于白天, 而6 月后仔鱼昼夜漂流密度无显著差异。本研究表明, 从三峡库尾进入三峡水库的鱼类早期资源丰富, 大部分鱼类繁殖发生在6 月以后水温较高、入库流量大、库区流速较高的时段, 库尾部分江段在流速较高时期, 仍存在四大家鱼的产卵场。