Diel activity and home range size in relation to food supply in a drift-feeding stream fish

Individuals within a species often compete for resources inboth space and time. In dominance hierarchies individuals withthe greatest competitive ability will occupy prime locationsduring optimal periods. We compared spatial and temporal useof habitat, aggression, and feeding success among giant kokopu(Galaxias argenteus) in dominance hierarchies under normal andreduced food supply. Under normal food supply conditions dominantfish were predominantly nocturnal and maintained large homeranges at night. Conversely, subdominant fish were diurnal andoccupied large home ranges by day but were generally not observedat night. When the food supply was limited, the utilizationof pools was determined by social rank. Dominant fish from eachpool increased diurnal activity, home range size, aggressiveness,and the capture of food items offered by day while simultaneouslyreducing the spatial and temporal activity and habitat use ofsubdominant fish. These results indicate that behavioral changesin large dominant fish influence and reduce the amount of resourcesavailable to subdominant fish.     

Microhabitat use by longfin eels in New Zealand streams with contrasting riparian vegetation

Longfin eels Anguilla dieffenbachii caught by electrofishing, in Lee Stream, a tributary of the Taieri River, New Zealand, were significantly longer in pools than in riffles, particularly in summer. Longfin eels were generally shorter in sites with willow. More longfin eels were caught at pasture sites than tussock sites with fewest at sites with willow. Sites judged difficult to access by commercial fishermen had longfin eels that were significantly longer than those in easy-access sites. More than 80% of longfin eels were captured within 270 mm of banks. The first three components of a principal component analysis explained 40·3% of the variability in microhabitat character recorded at both the capture location and within 0·5 m of capture, and from random locations in each riparian category. Variables strongly associated with longfin eel capture locations were maximum depth (longfin eels used microhabitat of intermediate depth), distance to pool (intermediate), sediment size (finer), sediment depth (deeper), stream idth (intermediate) and flow velocity (slower). Overall there was a greater icrohabitat range in tussock sites but diurnal microhabitat use was most similar to what was available in pasture streams. Winter longfin eel locations were characterized by deeper and finer sediments in contrast to summer and spring locations.     

Evaluation of visible implant elastomer for individual marking of small perch and common bully

Visible implant elastomer (VIE) was evaluated as a method for individual marking of small perch Perca fluviatilis and common bully Gobiomorphus cotidianus to use in capture–recapture studies. Growth, survival and mark retention was measured in 25 VIE marked and 15 unmarked fish of each species during a 125 day laboratory experiment. Marking had no effect on growth or survival of either species and mark retention in perch was 100%. Common bully mark retention was high for the initial 30 days but decreased to 72% by the end of the experiment. VIE marking provided an excellent method for individual identification of small perch over periods of at least 125 days, but improvements to common bully mark retention are necessary if VIE is to be used in capture–recapture studies >30 days.     

Riparian land use and accessibility to fishers influence size class composition and habitat use by longfin eels in a New Zealand river

Fyke nets were used to sample longfin eels Anguilla die.enbachii in fourth order stream sites with contrasting riparian land use (native tussock, exotic pasture and pasture plus willows Salix spp.) in Lee Stream, a tributary of the Taieri River, New Zealand. Total lengths (L_T) of longfin eels from locations inaccessible to eel fishers were normally distributed whereas those from accessible locations had a non-normal, positively skewed distribution. Mean L_T and body condition were higher in inaccessible than accessible sites, consistent with considerable fishing exploitation in the latter. Mean L_T of the fish was greatest in pasture, intermediate in willow and smallest in tussock sites. Larger longfin eels (≥535 mm) were associated with a riffle-type habitat consisting of shallow, faster-flowing water with coarse, variable sediment and were taken farther from cover. In contrast, smaller longfin eels were associated with a pool-type habitat consisting of slower-flowing, deeper water, with fine, homogenous sediment and were captured closer to cover. This pattern of habitat use differed from some previous reports and probably reflects differences in methodology: fyke nets set over 48 h to sample actively moving longfin eels compared to daytime electric fishing, which samples longfin eels that are more likely to be at rest.     

Decoding the Substrate Supply to Human Neuronal Nitric Oxide Synthase

Nitric oxide, produced by the neuronal nitric oxide synthase (nNOS) from L-arginine is an important second messenger molecule in the central nervous system: It influences the synthesis and release of neurotransmitters and plays an important role in long-term potentiation, long-term depression and neuroendocrine secretion. However, under certain pathological conditions such as Alzheimer’s or Parkinson’s disease, stroke and multiple sclerosis, excessive NO production can lead to tissue damage. It is thus desirable to control NO production in these situations. So far, little is known about the substrate supply to human nNOS as a determinant of its activity. Measuring bioactive NO via cGMP formation in reporter cells, we demonstrate here that nNOS in both, human A673 neuroepithelioma and TGW-nu-I neuroblastoma cells can be fast and efficiently nourished by extracellular arginine that enters the cells via membrane transporters (pool I that is freely exchangeable with the extracellular space). When this pool was depleted, NO synthesis was partially sustained by intracellular arginine sources not freely exchangeable with the extracellular space (pool II). Protein breakdown made up by far the largest part of pool II in both cell types. In contrast, citrulline to arginine conversion maintained NO synthesis only in TGW-nu-I neuroblastoma, but not A673 neuroepithelioma cells. Histidine mimicked the effect of protease inhibitors causing an almost complete nNOS inhibition in cells incubated additionally in lysine that depletes the exchangeable arginine pool. Our results identify new ways to modulate nNOS activity by modifying its substrate supply.     

Does social status within a dominance hierarchy mediate individual growth,residency and relocation?

The availability of food, and hence energy, is known to influence the abundance, habitat choice and growth of individuals. In contrast, there is a paucity of knowledge on how the interaction of energy supply and social status determines patterns of residency and movement. This study tests whether the presence of conspecifics and an individual’s social status in relation to food supply influence the fitness and movement of a drift-feeding fish (Galaxias fasciatus). Using an information-theoretic approach (AIC), our analysis indicated that the most parsimonious model of fish movement among pools was one that included food supply, social rank and fish relative growth rate. Our results indicated that subordinate fish relocated more frequently compared to dominant fish, most likely as a consequence of intra-specific competition that limited the access of these smaller fish to resources and constrained their growth. Our results suggest that energy constraints may force individuals to explore new habitats in an effort to find more energetically profitable patches. We conclude that intra-specific competition mediated through the social hierarchy amongst closely interacting individuals plays a key role in determining individual growth, residency and relocation.     

Evaluating the potential of night spotlighting as a method for assessing species composition and brown trout abundance: a comparison with electrofishing in small streams

Direct counts of fish obtained by night spotlighting were compared with species composition and population estimates obtained from three-pass electrofishing obtained across 29 sites along small clear streams in the Otago region of New Zealand. The influence of habitat variables on the relative efficiency of each method was also examined. The same seven species of fishes were identified by both methods. Juvenile brown trout Salmo trutta were the only species present in sufficient numbers to allow comparison of abundance estimates using the two methods. A total of 777 brown trout were counted by spotlight and 803 brown trout were caught using electrofishing. Estimates of abundance obtained by spotlighting reflected population estimates obtained by three-pass electrofishing across most habitats. Electrofishing produced higher population estimates relative to spotlighting in fast-flowing turbulent riffle habitats, whereas counts obtained by spotlighting tended to be higher relative to electrofishing in slow-flowing pool habitats. The results suggest that spotlighting is an effective method for assessing fish composition and brown trout abundance in small clear water streams, although the extremes of water velocity may influence efficiency of both spotlighting and electrofishing.