Contrasting intraspecific dietary shifts in two terapontid assemblages from Australia’s wet‐dry tropics

Abstract – This study assessed the size‐related patterns of dietary resource use in terapontid assemblages from two north Australian wet‐dry tropical river systems exhibiting contrasting long‐term flow regimes. Substantially higher size‐related dietary divergence in the form of additional trophic guilds and lower levels of dietary overlap were evident among terapontids from the comparatively stable Daly River system, particularly during the dry season. Relatively restricted expression of size‐related dietary shifts in conjunction with higher levels of dietary overlap and no significant seasonal effects on dietary overlap were features of assemblage interaction in the highly variable Burdekin River. Results highlight size‐related dietary shifts as a complex aspect of terapontid trophic habits, and one that can exhibit considerable spatial dynamism.     

Feeding ecology and coexistence dynamics in a community of fishes in a temperate temporary water body

Temporary water bodies are temporally variable ecosystems supported primarily by rainwater. The biota supported by such water bodies present a range of capacities to remain in this environment for all or part of their life cycles. During floods, temporary pools can connect with permanent streams, promoting changes in trophic networks in the aquatic food webs. The aim of this research was to analyse the feeding ecology of a fish community in a temporary pool near of Tlacotalpan, in the Mexican southeast, in order to understand the dynamics of the feeding habits. First, we identified feeding habits that can be interpreted as guilds of the fishes in the temporary pool: the annual killifish Millerichthys robustus (the only autochthonous species) is planktophagous; Cynodonichthys tenuis and Astyanax aeneus are insectivores; Dormitator maculatus and larvae of amphibians (Lithobates sp.) are mainly detritivorous; and Poecilia mexicana is planktophagous and insectivorous. We then estimated the effect of coexistence on niche breadth and overlap. The niches of M. robustus and P. mexicana evidenced overlap, but the breadth was adjusted inversely, suggesting feeding specialisation in M. robustus in response to competition. We documented the existence of two cohorts of M. robustus; the niche breadth of the first and second cohorts suggesting different strategies probably related to competition under variable conditions. The niche of C. tenuis and A. aeneus, and D. maculatus and tadpoles overlapped, following a pattern of feeding generalisation in response to competition.     

Food habits of fishes on unvegetated tidal mudflats in Tokyo Bay, central Japan

ABSTRACT:   To clarify the feeding habits of tidal mudflat fishes, the gut contents of 29 fish species, collected from unvegetated tidal mudflats in Tokyo Bay, central Honshu, Japan, were examined. Ontogenetic changes in food preference were recognized in 21 species, including several of commercial importance (e.g. Acanthogobius flavimanus , Konosirus punctatus , Mugil cephalus cephalus , Plecoglossus altivelis altivelis , and Sardinella zunasi ). In general, larvae and/or juveniles of these species fed mainly on small zooplankton or benthic harpacticoid copepods, later switching to other prey items with growth (e.g. gammaridean amphipods, mysids, polychaetes, detritus, bivalves, and juvenile fishes). A cluster analysis based on dietary overlaps showed that the tidal mudflat fish assemblage comprised six feeding guilds (small benthic and epiphytic crustacean, zooplankton, detritus, mollusc, polychaete, and fish feeders). Of these, small benthic and epiphytic crustacean feeders were the most abundantly represented in the number of species.     

Fishery development in the eastern North Pacific: a natural-cultural system perspective, 1888–1976

Commercial fishery landings data spanning almost a century were examined from three regions within the eastern North Pacific: north-central California, Oregon-Washington, and Southeast Alaska. Fisheries in each region developed differently because each region had unique species, community trophic composition, and other community parameters related to differences in physico-chemical characteristics. Fisheries also began at different times in each region. Despite differences, overall patterns of landings were similar among regions. A 'fishing-up' sequence occurred in each region that included seaward expansion of the fishery and diversification of taxonomic composition of landings. Mean annual landed weights of several very desirable taxa fished continuously from the early years of the fisheries initially increased, peaked, then declined. These patterns are similar to those found in studies of long-term fishery development in the Great Lakes. Other patterns of landings over time common to each region were: exclusions of particular taxa in more recent time periods; predominance of pelagic species; and shifts in trophic composition away from predominance of taxa at high trophic levels. In two regions there were initial increases, then declines in mean annual weights of total landings. Similarities in these patterns among regions that differ greatly in terms of physico-chemical characteristics suggest the overwhelming importance of common cultural parameters. Management suggestions are made based on the common patterns of commercial fishery development.     

Diel patterns in the feeding and habitat use of O-group fishes in a regulated river: the River Great Ouse, England

Feeding and habitat use behaviour of juvenile O+ fishes, principally Rutilus rutilus (L.) and Leuciscus cephalus (L.) was analysed at 4-h intervals for a period of 24 h on 29 June, 27 July, and 13 September 1994 at a regulated site on the River Great Ouse, UK. Twenty-five random point samples were taken by electrofishing during each sampling period from a 250 m reach of the river. Catch per unit effort decreased at night for both R. rutilus and L. cephalus. The number of prey items in the gut and the number of taxa found also decreased at night except for R. rutilus on one occassion. Habitat use remained near constant, with only slight increases in depth and distance from the bank at night. Use of Nuphar lutea by roach increased at night. Chub tended to avoid Nuphar lutea and were positively associated with emergent macrophyte and algal cover both during the day and night.