Drinking in Antarctic fishes

Drinking rates have never been measured in Antarctic fish. Drinking rates were measured in four species of notothenioid fish, including a hemoglobinless icefish, found in the near-freezing waters of the Ross Sea of the Southern Ocean. All of the fish, with the exception of the icefish, had low drinking rates and high serum osmolalities relative to temperate seawater fish. The icefish had significantly higher drinking rates and serum osmolalities relative to the Antarctic fishes containing hemoglobin, including Trematomus bernacchii. Warm acclimation of T. bernacchii, from −1.5°C to +4°C for 4 weeks, significantly increased their drinking rates 4.6-fold, significantly decreased their serum and intestinal osmolality by 11% and 12%, respectively, relative to cold-acclimated fish. These results indicate that increased drinking rates in Antarctic fish at elevated temperatures are involved in maintaining a lower serum osmolality.     

Comparative phylogeography of Atlantic reef fishes indicates both origin and accumulation of diversity in the Caribbean

Background  

Two processes may contribute to the formation of global centers of biodiversity: elevated local speciation rates (the center of origin hypothesis), and greater accumulation of species formed elsewhere (the center of accumulation hypothesis). The relative importance of these processes has long intrigued marine biogeographers but rarely has been tested.     

Response of coastal fishes to the Gulf of Mexico oil disaster

The ecosystem-level impacts of the Deepwater Horizon disaster have been largely unpredictable due to the unique setting and magnitude of this spill. We used a five-year (2006-2010) data set within the oil-affected region to explore acute consequences for early-stage survival of fish species inhabiting seagrass nursery habitat. Although many of these species spawned during spring-summer, and produced larvae vulnerable to oil-polluted water, overall and species-by-species catch rates were high in 2010 after the spill (1,989±220 fishes km-towed(-1) [μ ± 1SE]) relative to the previous four years (1,080±43 fishes km-towed(-1)). Also, several exploited species were characterized by notably higher juvenile catch rates during 2010 following large-scale fisheries closures in the northern Gulf, although overall statistical results for the effects of fishery closures on assemblage-wide CPUE data were ambiguous. We conclude that immediate, catastrophic losses of 2010 cohorts were largely avoided, and that no shifts in species composition occurred following the spill. The potential long-term impacts facing fishes as a result of chronic exposure and delayed, indirect effects now require attention.     

Tempo and mode of diversification of lake Tanganyika cichlid fishes

Background

Understanding the causes of disparities in species diversity across taxonomic groups and regions is a fundamental aim in evolutionary biology. Addressing these questions is difficult because of the need for densely sampled phylogenies and suitable empirical systems.

Methodology/Principal Findings

Here we investigate the cichlid fish radiation of Lake Tanganyika and show that per lineage diversification rates have been more than six times slower than in the species flocks of Lakes Victoria and Malawi. The result holds even at peak periods of diversification in Lake Tanganyika, ruling out the age of the lake as an explanation for slow average rates, and is robust to uncertainties over the calibration of cichlid radiations in geological time. Moreover, Lake Tanganyika lineages, irrespective of different biological characteristics (e.g. sexually dichromatic versus sexually monochromatic clades), have diversified at similar rates, falling within typical estimates across a range of plant and animal clades. For example, the mostly sexually dichromatic haplochromines, which have speciated explosively in Lakes Victoria and Malawi, have displayed modest rates in Lake Tanganyika (where they are called Tropheini).

Conclusion/Significance

Our results show that either the Lake Tanganyika environment is less conducive for cichlid speciation or the remarkable diversifying abilities of the haplochromines were inhibited by the prior occupancy of older radiations. Although the results indicate a dominant role for the environment in shaping cichlid diversification, differences in the timing of diversification among the Tanganyikan tribes indicate that biological differences were still important for the dynamics of species build-up in the lake. While we cannot resolve the timing of the radiation relative to the origin of the lake, because of the lack of robust geological date calibrations for cichlids, our results are consistent with a scenario that the different clades reflect independent adaptive radiations into different broad niches in the lake.     

Comparative phylogeography of Nearctic and Palearctic fishes

Combining phylogeographic data from mitochondrial DNA (mtDNA) of Nearctic and Palearctic freshwater and anadromous fishes, we used a comparative approach to assess the influence of historical events on evolutionary patterns and processes in regional fish faunas. Specifically, we (i) determined whether regional faunas differentially affected by Pleistocene glaciations show predictable differences in phylogeographic patterns; (ii) evaluated how processes of divergence and speciation have been influenced by such differential responses; and (iii) assessed the general contribution of phylogeographic studies to conservation issues. Comparisons among case studies revealed fundamental differences in phylogeographic patterns among regional faunas. Tree topologies were typically deeper for species from nonglaciated regions compared to northern species, whereas species with partially glaciated ranges were intermediate in their characteristics. Phylogeographic patterns were strikingly similar among southern species, whereas species in glaciated areas showed reduced concordance. The extent and locations of secondary contact among mtDNA lineages varied greatly among northern species, resulting in reduced intraspecific concordance of genetic markers for some northern species. Regression analysis of phylogeographic data for 42 species revealed significant latitudinal shifts in intraspecific genetic diversity. Both relative nucleotide diversity and estimates of evolutionary effective population size showed significant breakpoints matching the median latitude for the southern limit of the Pleistocene glaciations. Similarly, analysis of clade depth of phylogenetically distinct lineages vs. area occupied showed that evolutionary dispersal rates of species from glaciated and nonglaciated regions differed by two orders of magnitude. A negative relationship was also found between sequence divergence among sister species as a function of their median distributional latitude, indicating that recent bursts of speciation events have occurred in deglaciated habitats. Phylogeographic evidence for parallel evolution of sympatric northern species pairs in postglacial times suggested that differentiation of cospecific morphotypes may be driven by ecological release. Altogether, these results demonstrate that comparative phylogeography can be used to evaluate not only phylogeographic patterns but also evolutionary processes. As well as having significant implications for conservation programs, this approach enables new avenues of research for examining the regional, historical, and ecological factors involved in shaping intraspecific genetic diversity.     

Aspects of the biology and ecology of Caribbean reef fishes: Serranidae (hinds and groupers)

Hinds and groupers (Teleostei, Serranidae) form a valuable component of catches of reef fishes in the Caribbean Sea and adjacent regions. Investigations of species in Jamaican waters have covered relative and absolute growth rates, spawning seasons, fecundity, size at maturity and at sex change, and size compositions, mortality rates, and relative abundances of exploited and unexploited populations.     

Grazing pressure of herbivorous coral reef fishes on low coral-cover reefs

The impact of grazing by herbivorous fishes (Acanthuridae, Scaridae, and Pomacentridae) on low coral-cover reefs was assessed by measuring rates of benthic algal production and consumption on inshore and offshore reefs in the upper Florida Keys. Algal production rates, determined in situ with caged and uncaged experimental plates, were low (mean 1.05 g C m⁻² day⁻¹) and similar among reef types. Algal consumption rates were estimated using two different models, a detailed model incorporating fish bite rates and algal yield-per-bite for one species extrapolated to a guild-wide value, and a general regression relating fish biomass to algal consumption. Algal consumption differed among reef types: a majority of algal production was consumed on offshore reefs (55–100%), whereas consumption on inshore patch reefs was 31–51%. Spatial variation in algal consumption was driven by differences in herbivorous fish species composition, density, and size-structure among reef types. Algal consumption rates also varied temporally due to seasonal declines in bite rates and intermittent presence of large-bodied, vagile, schooling species. Spatial coherence of benthic community structure and temporal stability of algal turf over 3 years suggests that grazing intensity is currently sufficient to limit further spread of macroalgal cover on these low coral-cover reefs, but not to exclude it from the system.     

Morphological characterization of the alimentary tract of Antarctic fishes and its relation to feeding habits

Summary Morphological and morphometric characteristics of the alimentary tract in 22 species of carnivorous antarctic fishes were studied. It is shown that all of these species have similar, well-developed Y-shaped stomachs with generally thick (0.5–1.0 mm) walls. The relative stomach lengths are also similar, ranging from 9.8 to 22.2% of body length. Relative intestine lengths, a characteristic frequently used as an indicator of the kind of food eaten by a species, are also remarkably similar among most species (31 to 67%). Notothenia gibberifrons, a conspicuous benthos feeder, has a significantly longer intestine (91%), probably as an adaptation to the quantity of undigestible material (mud) incorporated with its faunal prey. These values fit within or below the limits (60–150$) of relative intestine length described in the literature for carnivorous fishes. The number of pyloric caecae is in general relatively low and fairly constant in each species. It is concluded that the morphological features studied could represent similar adaptations of these antarctic fishes to a similar carnivorous diet.     

Effects of microhabitat and metabolic rate on food intake,growth and fecundity of two competing coral reef fishes

Spinyhead blennies (Acanthemblemaria spinosa) and roughhead blennies (A. aspera) are planktivorous hole-dwelling fishes that live in dead coral skeletons. Both species are known to choose shelters high above the reef surface (although spinyheads displace roughheads downwards). To test the hypothesis that this preference is due to greater plankton availability in higher locations, fish were placed on artificial habitats located 15 cm and 100 cm above the surface of a natural reef. Both species experienced higher feeding rates, growth rates, and fecundities in high locations, and spinyhead rates generally exceeded roughhead rates at a given height. Under laboratory conditions, oxygen consumption by spinyheads was 1.6 times greater than that of roughheads and this corresponds well with the 1.8 ratio of feeding rates under controlled aquarium conditions. This information provides a partial explanation for the observed microhabitat distribution and resulting coexistence of these competing species: it is hypothesized that spinyheads have an advantage in agonistic interactions because of their higher metabolic rates, thus excluding roughheads from high sites, but that roughheads can persist at low sites because their lower metabolic rates result in lower food demands. A model is presented that predicts varying occurrences and vertical distributions of these species in locations with different zooplankton densities.     

Comparing the performance of multiple mitochondrial genes in the analysis of Australian freshwater fishes

In this study, four mitochondrial genes (cytochrome oxidase I, ATPase, cytochrome b and control region) were amplified from most of the fish species found in the fresh waters of south-eastern Queensland, Australia. The performance of these different gene regions was compared in terms of their ability to cluster fish families together in a neighbour-joining tree, both individually by gene and in all combinations. The relative divergence rates of each of these genes were also calculated. The three coding genes (cytochrome oxidase I, ATPase and cytochrome b) recovered similar number of families and had broadly similar divergence rates. ATPase diverged a little more quickly than cytochrome oxidase I and cytochrome b slightly more slowly than cytochrome oxidase I. All two-gene combinations recovered the same number of families. Results from the control region were much more variable, and, although generally possessing more diversity than the other regions, were sometimes less variable.     

Does mobility explain variation in colonisation and population recovery among stream fishes?

1. Colonisation and population recovery are crucial to species persistence in environmentally variable ecosystems, but are poorly understood processes. After documenting movement rates for several species of stream fish, we predicted that this variable would influence colonisation rates more strongly than local abundance, per cent occupancy, body size and taxonomic family. We also predicted that populations of species with higher movement rates would recover more rapidly than species with lower movement rates and that assemblage structure would change accordingly. 2. To test these predictions, we removed fishes from a headwater and a mainstem creek in southwest Virginia and monitored colonisation over a 2‐year period. Using an information–theoretic approach, we evaluated the relative plausibility of 15 alternative models containing different combinations of our predictor variables. Our best‐supported model contained movement rate and abundance and was 41 times more likely to account for observed patterns in colonisation rates than the next‐best model. Movement rate and abundance were both positively related to colonisation rates and explained 88% of the variation in colonisation rates among species. 3. Population recovery, measured as the per cent of initial abundance restored, was also positively associated with movement rate. One species recovered within 3 months, most recovered within 2 years, but two species still had not recovered after 2 years. Despite high variation in recovery, the removal had only a slight impact on assemblage structure because species that were abundant in pre‐removal samples were also abundant in post‐removal samples. 4. The significance of interspecific variation in colonisation and recovery rates has been underappreciated because of the widely documented recovery of stream fish assemblages following fish kills and small‐scale experimental defaunations. Our results indicate that recovery of the overall assemblage does not imply recovery of each component species. Populations of species that are rare and less mobile will recover more slowly and will be more vulnerable to extinction in systems where chemical spills, hydrological alteration, extreme droughts and other impacts are frequent.     

Suitability of surgically implanted 8-mm passive integrated transponder tags for small-bodied fishes

Innovative tools that benefit conservation are critical as freshwater fishes are lost at unprecedented rates. Mark-recapture methods can characterize population demographics and life-history traits of diverse fishes, but suitable techniques for tagging for individual recognition of small-bodied fishes are rare. Passive integrated transponder (PIT) tag technology may facilitate the tagging of small fishes and early life stages of larger species. However, relatively little research has evaluated the suitability of these small (8.4 × 1.4 mm) tags for many groups of small fishes. Tag loss (retention and survival) and growth of individuals implanted with PIT tags relative to control and sham treatments were compared for eight fishes of differing morphologies. Additionally, the utility of cyanoacrylate to improve tag retention was tested on a subset of taxa. Fish of each species were equally divided and randomly assigned to one of three treatment groups (handled [control], surgical incision [sham], or surgical incision and PIT tag implantation [PIT]). During the 42-d study period, mortalities and expelled tags were counted daily and growth was measured weekly. Researchers can generally expect little tag loss and uncompromised growth rates for a variety of small-bodied fishes; however, initial fish length was related to the magnitude of physiological effects for some taxa (i.e., blacknose dace Rhinichthys atratulus, johnny darter Etheostoma nigrum, juvenile white sucker Catostomus commersonii). Relatively poor survival (<80%) was observed for two benthic species: johnny darter and blacknose dace, often when incision wounds became inflamed before healing. Prevalent tag loss for johnny darter, tadpole madtom Noturus gyrinus, and a dorsal-laterally compressed cyprinid can be reduced by closing the wounds with cyanoacrylate, but with substantially increased mortality rates. This research demonstrates the broad applicability of PIT tagging technology for ecological studies of small-bodied fishes and alleviates many concerns when surgically implanting tags into several fishes.     

Influences of body mass,temperature, oxygen tension,and salinity on respiratory oxygen consumption of cyprinodontoid fishes of three families

This review evaluates the current state of knowledge of influences of body mass, ambient temperature, P_O2, and salinity on routine metabolic rates of members of three families, Fundulidae, Cyprinodontidae, and Poeciliidae, belonging to the order Cyprinodontiformes. The study was motivated by Winberg’s (Fisheries Research Board of Canada, Translation Series No. 194. Distributed by the Fisheries Research Board of Canada Biological Station, Nanaimo, BC, 1960) conclusion that the Cyprinodontiformes (Winberg included only live-bearing poeciliids) generally have lower metabolic rates that do other fishes. Based on available information Winberg’s conclusion was borne out that live-bearing freshwater poeciliids show lower than average routine metabolic rates compared to other freshwater fish groups. This is also true of poeciliids from saline waters, and of both freshwater and saline-water members of the related families Fundulidae and Cyprinodontidae. However, considerable variation in metabolic patterns was noted within and among these three families. There were geographic variations between subspecies of some species. Some island groups/species showed lower routine metabolic rates than did allied mainland groups/species. Thermal responses (Q₁₀ values) in routine metabolic rates of these fishes showed variations with geographic location, P_O2, salinity and size. Values of P_O2crit were altered among species by temperature, body size/age, and possibly salinity. Influences of ambient salinity on routine metabolic rates of these cyprinodontoid fishes also showed variations with temperature and size/age of individuals. The patterns of metabolic responses in these cyprinodontoid fishes to environmental conditions were generally similar to those of other species. Unfortunately, the available information on these fishes lacks the uniformity that would allow for critical and quantitative comparisons between and among the cyprinodontoids and with other species.     

Behaviour of temperate and sub-tropical reef fishes towards a stationary SCUBA diver

Using remote underwater stereo–video systems we examined fish behaviour towards a stationary SCUBA diver at temperate (Rottnest Island) and sub-tropical (Houtman Abrolhos Islands) reefs in Western Australia. Changes in species richness, relative abundance, fish length, and the mean distance of individual fish from stereo–video cameras, in the presence and absence of a SCUBA diver, were assessed to infer changes in behaviour. Results show that a stationary SCUBA diver may obtain accurate measures of species richness and of the composition of fish assemblages in an area. However, the usefulness of these measures to reflect changes in fish behaviour appears limited as responses of fish towards the stationary SCUBA diver were highly species specific. Several species differed in their mean relative abundance (Heterodontus portusjacksoni, Coris auricularis, Thalassoma lunare), length (Ophthalmolepsis lineolatus, C. auricularis), and the distance to which they would approach the stereo–video systems (Kyphosus sydneyanus, Scarus schlegeli) when a SCUBA diver was present. Here, species-specific changes in the behaviour of several common and abundant fish species towards a stationary SCUBA diver advises caution to avoid biases when interpreting results obtained by SCUBA divers.     

Triacylglycerol lipase activities in tissues of Antarctic fishes

. The activity of the lipolytic enzyme, triacylglycerol lipase (TAG lipase; E.C. 3.1.1.3) was measured in heart ventricle, liver, oxidative skeletal muscle, and adipose tissue of four species of Antarctic fishes (Chaenocephalus aceratus, Notothenia coriiceps, Trematomus newnesi, Gobionotothen gibberifrons). Estimates of weight-specific activities at 0°C in tissues of the Antarctic fishes were broadly comparable to those reported for temperate-zone fish species assayed at their physiological temperature. Within each species, liver tissue displayed the highest weight-specific activity of TAG lipase in C. aceratus, T. newnesi, and G. gibberifrons, while adipose tissue of N. coriiceps showed the highest activity within that species. Combining these estimates with carefully measured somatic indices of the tissues, permitted assessment of the relative importance of different tissues to overall lipolytic capacity on an organismal level. On this basis, liver tissue displays the greatest capacity of TAG lipase per 100 g body weight in each of the species studied.     

Swimming performance and metabolic rate of three tropical fishes in relation to temperature

Oxygen consumption was measured for three tropical fishes,Exodon paradoxus, Leporinus fasciatus andLabeo erythrurus in relation to swimming speed and temperature. For each species the logarithm of oxygen consumption (mg 0₂ · g^–1 · h^–1) increased linearly with relative swimming speed (1 · s^–1) with the value of the regression coefficients varying inversely with temperature. Active metabolism and critical swimming speed ofE. paradoxus andL. fasciatus increased with temperature to a maximum at 30 and 35° C respectively. Basal metabolic rates ofE. paradoxus andL. fasciatus increased with temperature. Metabolic rates and critical swimming speed of the three fishes studied were consistent with values for polar, temperate and other tropical species over their respective thermal ranges of tolerance. Tropical fishes have lowered their metabolism and swimming performance from that expected for many temperate species at the same temperature.     

Morphological analyses of the neurocranium of a group of rock-dwelling cichlid fishes (Gichlidae: Perciformes) from Lake Malawi, Africa

Variation in the size and the shape of neurocrania of a group of rock-dwelling cichlid fishes (mbuna; from Lake Malawi, Africa was analysed using principal components and regression analyses on a set of 24 neurocranial measurements of 86 individuals from 11 species. The results reveal effective morphological discrimination between species. Most of the structural variation between species demonstrates positive allometry and represents size-dependent species differences. Thus, morphological differentiation in these fish may be largely the result of heterochronic changes in relative growth rates. The vomerine region, however, exhibited shape differentiation. Distinct groupings, based on vomer shape, are identified. Foraging behaviour and diet are found to be correlated with this region of the neurocrania. The correlation of the shape of the vomer and fine-scale resource partitioning suggests that this structure may be important in the evolutionary success of the group. Also, most structural shape variation in neurocranial morphology is associated with structural variation in buccal jaws.     

Morphological analyses of the neurocranium of a group of rock-dwelling cichlid fishes (Cichlidae: Perciformes) from Lake Malawi,Africa

Variation in the size and the shape of neurocrania of a group of rock-dwelling cichlid fishes (mbuna; from Lake Malawi, Africa was analysed using principal components and regression analyses on a set of 24 neurocranial measurements of 86 individuals from 11 species. The results reveal effective morphological discrimination between species. Most of the structural variation between species demonstrates positive allometry and represents size-dependent species differences. Thus, morphological differentiation in these fish may be largely the result of heterochronic changes in relative growth rates. The vomerine region, however, exhibited shape differentiation. Distinct groupings, based on vomer shape, are identified. Foraging behaviour and diet are found to be correlated with this region of the neurocrania. The correlation of the shape of the vomer and fine-scale resource partitioning suggests that this structure may be important in the evolutionary success of the group. Also, most structural shape variation in neurocranial morphology is associated with structural variation in buccal jaws.     

Age-specific mortality rates in reef fishes: Evidence and implications

Abstract Mortality is a fundamental demographic rate, the nature of which has profound consequences for both the dynamics of populations and the life-history evolution of species. For example, if per capita mortality rates are age- or stage-specific, life-history traits should evolve in response to age- and stage-specific differences in selection arising from these temporally variable rates. Similarly, variation in the average mortality rate across ages and/or stages can also select for shifts in life history. Mortality rates of recently settled reef fishes can be very high and per capita mortality is commonly assumed to decrease with increasing age. A review of evidence for age-specific per capita mortality rates in reef fishes from early postsettlement up to 13 months postsettlement suggests that during this period these rates are often age invariant. The data on which these interpretations are based, however, are extremely limited both in terms of the proportion of the life cycle over which mortality rates have been sampled and the quality of these data. Nonetheless, these data do suggest that selective pressures associated with patterns of mortality may vary among species of reef fishes and that these species therefore could be more effectively used in the study of life-history evolution. At present, reef fishes are under-represented in the study of life-history evolution compared with other vertebrate taxa.