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  • 1.
    Almqvist, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Strandmark, Alma K.
    Appelberg, Magnus
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Has the invasive round goby caused new links in Baltic food webs?2010In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 89, no 1, p. 79-93Article in journal (Refereed)
    Abstract [en]

    The Ponto-Caspian round goby (Neogobius melanostomus, Pallas 1814) most probably was established in the Gulf of GdaA""sk, Baltic Sea, in the late 1980's and has since become one of the dominant species in the region. In this study we assess the role of round gobies as prey for two important fish species in the Gulf of GdaA""sk, cod (Gadus morhua) and perch (Perca fluviatilis). We compared their present diet with stomach analyses from the area prior the round goby establishment, as well as with diet analysis from Baltic regions where round gobies are absent. There were large differences in the diet between cods from the Gulf of GdaA""sk 2003-2006 compared to cods in earlier studies (1977-1981) from the Southern Baltic Sea. There were also large differences in cod and perch diets from areas with and without round goby. Presently, round goby constitutes the most important prey for medium sized cods in Gulf of GdaA""sk, and perch from the same area almost exclusively feed on gobiids. Stomach analysis, trophic level estimates, and stable isotope analyses all indicated that cod and perch in Gulf of GdaA""sk after the round goby establishment belonged to a similar trophic level. Beside round goby, no mussel feeding fish contributed much to the diet of cod or at all to the diet of perch. Thus, it is likely that round gobies constitute a new energetic pathway from mussels to top predators. However, due to the short time elapsed after round goby establishment, we can only speculate on the species future impacts on Baltic food webs.

  • 2.
    Amcoff, Mirjam
    et al.
    Uppsala universitet, Zooekologi.
    Kolm, Niclas
    Uppsala universitet, Zooekologi.
    A test of sensory exploitation in the swordtail characin (Corynopoma riisei) based on colour matchingbetween female prey and a male ornament2014In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 97, no 3, p. 247-254Article in journal (Refereed)
    Abstract [en]

    The sensory exploitation hypothesis states that pre-existing biases in female sensory systems may generate strong selection on male signals to match such biases. As environmental conditions differ between populations, sexual preferences resulting from natural selection are expected to vary as well. The swordtail characin (Corynopoma riisei) is a species in which males carry a flag-like ornament growing from the operculum that has been proposed to function as a prey mimic to attract females. Here, we investigated if female plasticity in feeding preferences is associated with plasticity in preference for an artificial male ornament in this species. Females were trained for 10 days by offering them differently coloured food items and were then tested for changes in preferences for differently coloured artificial male ornaments according to foraging experience. We found a rapid and pronounced change in female preference for the colouration of the artificial ornament according to food training. Thus our results support the possibility that sensory exploitation may act as a driving force for female preferences for male ornaments in this species.

  • 3.
    Amcoff, Mirjam
    et al.
    Uppsala University, Sweden.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Multiple male sexual signals and female responsiveness in the swordtail characin, Corynopoma riisei2015In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 98, no 7, p. 1731-1740Article in journal (Refereed)
    Abstract [en]

    In the courtship process, multiple signals are often used between the signaller and the receiver. Here we describe female response to multiple male visual morphological and behavioural signals in the swordtail characin, Corynopoma riisei. The swordtail characin is a species in which males display several morphological ornaments as well as a rich courtship repertoire. Our results show that high courtship intensity was associated with an increased female response towards the male ornament, increased number of mating attempts and a reduction in female aggression. The morphological aspects investigated here did not seem to correlate with female response. This may indicate that, when both behaviour and morphology are considered simultaneously, courtship behaviour may have priority over morphological cues in this species.

  • 4.
    Costalago, David
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Nelson Mandela Metropolitan University, South Africa.
    Potter, Paige
    Pattrick, Paula
    Strydom, Nadine A.
    Influence of environmental variables on the larval stages of anchovy, Engraulis encrasicolus, and sardine, Sardinops sagax, in Algoa Bay, South Africa2018In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 101, no 2, p. 225-236Article in journal (Refereed)
    Abstract [en]

    We investigated the environmental drivers of larval abundance of anchovy Engraulis encrasicolus and sardine Sardinops sagax in Algoa Bay, Eastern Cape (South Africa). This study comprised a pre-drought post-drought time period, comparing the responses of the fish larvae to different factors before and after the drought. The current study presents, for the first time, which environmental variables are affecting the anchovy and sardine larvae populations in the region. Easterly wind speed and zooplankton density were the only environmental variables that presented a significant change between the pre- and post-drought periods, increasing after the drought. Generalized additive models (GAMs) were used in order to explore the effects that environmental factors might have in the abundance of anchovy and sardine larvae in Algoa Bay. Specifically, the GAM that best explained the deviance of the anchovy larvae dynamics included the covariates rainfall, easterly wind speed, Chl a concentration, sardine larvae abundance and the interactions SST*Chla and sard*SST. The GAM best explaining sardine larvae abundance included only the easterly wind speed as a covariate. This model showed that there was a positive relationship between the higher values of wind speed and sardine larvae abundance.

  • 5.
    Kolm, Niclas
    et al.
    Uppsala universitet, Zooekologi.
    Arnqvist, Göran
    Uppsala universitet, Zooekologi.
    Environmental correlates of diet in the swordtail characin (Corynopoma riisei, gill)2011In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 92, no 2, p. 159-166Article in journal (Refereed)
    Abstract [en]

    In the sexually dimorphic swordtail characin (Corynopoma riisei, Gill), males are equipped with an opercular flag-ornament that has been suggested to function as a food-mimic since females bite at the ornament during courtship. However, virtually nothing is known about the diet in wild populations of this species. In this study, we first investigated composition of and variation in the diet of C. riisei across 18 different populations in Trinidad, using gut content analyses. We then related variation in gut content to habitat features of populations to investigate the potential link between environmental conditions and prey utilization. Our results showed that the dominating food type in the gut was various terrestrial invertebrates, both adults and larvae, but we also document substantial variation in prey types across populations. Furthermore, a canonical correlation analysis revealed a relationship between environmental characteristics and diet: populations from wider and more rapidly flowing streams with more canopy cover tended to have a diet based more on ants and mosquitoes while populations from narrow and slow flowing streams with little canopy cover tended to have a diet based more on springtails, mites and mayfly larvae. Our results add novel information on the ecology of this interesting fish and suggest the possibility of local adaptation reflecting differences in prey availability across natural populations.

  • 6.
    Kolm, Niclas
    et al.
    Uppsala universitet, Zooekologi.
    Berglund, Anders
    Uppsala universitet, Zooekologi.
    Sex-specific territorial behaviour in the Banggai cardinalfish, Pterapogon kauderni2004In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 70, no 4, p. 375-379Article in journal (Refereed)
    Abstract [en]

    In a field experiment, we studied how levels of aggression in males and females in established pairs of the Banggai cardinalfish were influenced by the sex of an experimentally introduced individual larger and more attractive than its resident counterpart. Contrary to previous studies on other cardinalfish species, and contrary to expectations in a sex role reversed species, the male was the main aggressor towards an intruder. Moreover, residents were more aggressive towards an intruder of the same sex as themselves. Furthermore, even though females often courted introduced, larger males, no intruder managed to take over the partnership of any resident. We suggest that our findings imply relatively equal sex roles in the Banggai cardinalfish and we discuss the evolution of sex specific territory defence and its significance in the Banggai cardinalfish as well as the implications of such behaviour in the interpretations of sex roles in general.

  • 7.
    Lissåker, Maria
    Stockholm University, Faculty of Science, Department of Zoology.
    Does time of the season influence filial cannibalism in the sand goby, Pomatoschistus minutus?2007In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 80, no 1, p. 69-75Article in journal (Refereed)
    Abstract [en]

    According to life-history theory, filial cannibalism by fish that breed over one season only should be more beneficial early than late in the season if they eat eggs to invest energy into later clutches. Also, filial cannibalism may be more costly late in the season if finding ripe females for replacing eaten eggs is harder then. On the other hand, offspring hatching early may have a competitive advantage over fry hatching late and hence provide higher fitness to the parent. Using data collected over three successive years, I tested if sand goby males are more prone to eat of their eggs early than late in the reproductive season. I found no difference in the amount of eggs eaten or in the frequency of males eating the whole clutch between early and late in the season. Furthermore, there was no difference in the frequency of males who ate parts of their clutches, early compared to late. This might reflect a tradeoff between quality (early hatching offspring) and quantity (producing as many offspring as possible over a long reproductive season). If so, the lack of seasonal pattern of filial cannibalism found in sand gobies might be the result of opposing selection pressures.

  • 8.
    Näslund, Joacim
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of Gothenburg, Sweden.
    Rosengren, Malin
    Johnsson, Jörgen I.
    Fish density, but not environmental enrichment, affects the size of cerebellum in the brain of juvenile hatchery-reared Atlantic salmon2019In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 102, no 5, p. 705-712Article in journal (Refereed)
    Abstract [en]

    This paper describes a study on the environmentally dependent brain size plasticity in hatchery-reared Atlantic salmon Salmo salar L. Using a factorial experimental design, we tested whether tank fish density, local hatchery standard (150 fish . m(-2)) vs. reduced (50 fish . m(-2)) and structural enrichment, a bundle of submerged plastic stripes, had effects on the size of the cerebellar region of the brain. Fish reared at reduced density had smaller cerebella, while structural enrichment had no detectable effects. The density effect on cerebellum, which is involved in locomotion and cognition, confirms previous results from hatchery-reared Atlantic salmon. The lack of detectable positive effects of enrichment, which contrasts some previous studies, provide further evidence for a complex relationship between environmental complexity and brain growth.

  • 9.
    Öhman, Marcus C.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Rajasuriya, Arjan
    National Aquatic Resources Agency, Sri Lanka.
    Relationships between habitat structure and fish communities on coral and sandstone reefs1998In: Environmental Biology of Fishes, ISSN 0378-1909, E-ISSN 1573-5133, Vol. 53, p. 19-31Article in journal (Refereed)
    Abstract [en]

    The influence of habitat structure on reef-fish communities at Bar Reef Marine Sanctuary, Sri Lanka, was investigated. The relationship between habitat characteristics and the distribution and abundance och 135 species of fishes was examined on two reef types: coral and sandstone reefs. Results suggested that the reef fish communities were strongly influenced by various aspects of reef structure. However, relationships between habitat variables and fish communities structure, varied between the two reef types. Fish species diversity was correlated with a number of habitat variables on the sandstone reefs, although structural complexity seemed to play the dominant role. There were no correlations between habitat structure and fish diversity on the coral reefs. Total abundance was not related to any one habitat parameter on either reef type. However, abundances of some species, families and trophic groups were correlated with habitat features. These specific correlations were commonly related to food and shelter availability. For example, coral feeders were correlated with live coral cover, and pomacentrid species, which used branching corals for protection, showed a significant relationship with the density of Acropora colonies. This shows that a summary statistic such as total abundance may hide important information. Effects of habitat structure on the distribution patterns of the fish communities was further investigated using multidimensional scaling ordination and the RELATE-procedure. With the MDS-ordinations for both habitat and fish community composition it was possible to show that the multivariate pattern between the two ecological components was clearly correlated.

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