Condition factor and whole-body sodium concentrations in a freshwater fish: Evidence for acidification stress and possible ionoregulatory over-compensation

Condition factor, K, was measured for 1202 blacknose dace (Rhinichthys atratulus) from three streams in Shenandoah National Park (USA) of different acid neutralizing capacities (ANCs). K is a ratio of weight standardized to length; it is an indication of the health of the individuals in a population. R. atratulus condition factor in the low-ANC stream was found to be significantly lower (11%) than that of dace measured for fish from the intermediate- and high-ANC streams. This difference, according to the results of related investigations, is likely to be biologically significant. Whole-body sodium concentrations were measured as an additional test of sublethal stress in these streams. During summer base flow conditions, mean whole-body sodium concentrations of adult R. atratulus maintained in cages were found to be highest in the low-ANC stream and lowest in the high-ANC stream. The lower condition factor of dace in the low-ANC stream may be related to whole-body sodium concentration and ion regulation. Ion regulation in the low-ANC stream may be more metabolically costly because of chronic sublethal pH stress. R. atratulus may maintain high body Na⁺ concentrations in low ANC- and ionic strength waters in order to provide a buffer against large episodic pH depressions. The metabolic cost of this ionoregulatory over-compensation may necessitate the diversion of energy from somatic growth and explain the poorer condition of fish from such waters.     

Contents of heavy metal elements in copper mosses: Scopelophila ligulata,Scopelophila cataractae,and Mielichhoferia japonica and their substrates

Scopelophila ligulata (Spruce) Spruce, S. cataractae (Mitt.) Broth., and Mielichhoferia japonica Besch. (Mielichhoferia mielichhoferi (Hook.) Wijk et Marg. var. japonica (Besch.) Wijk et Marg.) are well known “copper mossess” which show peculiar ecological characteristics consisting of a preference for metal-rich soils, lithosols, rocks, etc. as their substrates. The total and water-soluble element contents in the substrates and heavy metal contents in the moss body were analyzed in this study. The results of these chemical analyses were as follows: The iron contents in the moss body and substrate of S. ligulata were higher than those of S. cataractae and M. japonica. On the contrary the copper contents of the former were lower than those of the latter. The pH values of substrate of S. ligulata were lower than those of S. cataractae and M. japonica. The concentrations of water-soluble iron and sulfate in the substrate of S. ligulata were higher than those of S. cataractae and M. japonica. On the contrary, the water-soluble copper concentrations in the substrate of S. ligulata were lower than those of the others. Although in the substrate of S. cataractae the iron content was several times higher than the copper content, in the moss body the copper content was higher than iron content.     

The association of water chemistry variables and fish condition in streams of Shenandoah National Park (USA)

As part of the Shenandoah National Park: Fish in Sensitive Habitats (SNP:FISH) project, the blacknose dace (Rhinichthys atratulus) was utilized as an indicator species to assess the susceptibility of the ichthyofaunal community of Shenandoah National Park (USA) to acidification. Water chemistry (ANC, conductivity, pH, and concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^–, NO₃ ^–, SO₄ ^2–, and SiO₂) was sampled every three months over the course of 3 1/4 years which represents the probable maximum lifetime of R atratulus. Condition factors (K=[g/mm³]^*10⁶) were calculated for samples of fish (age class 2+ yr; n=370) from nine montane, second/third order streams representing a range of ANCs. A principle components regression was performed on factor scores from a principle components analysis of the water chemistry variables and fish condition factor. Two factors, one associated with stream water ANC and ion concentrations, and another associated with SO₄ ^2– concentration, collectively explained 84% of the variance in condition factor. The influence of variables other than water chemistry upon R atratulus K is addressed. The results show that environmental chemistry is highly associated with the K of R atratulus.     

Reproductive timing in three southern Appalachian stream fishes

We quantified the reproductive biology of mottled sculpin (Cottus bairdi), rosyside dace (Clinostomus funduloides) and longnose dace (Rhinichthus cataractae) in Coweeta Creek, North Carolina, USA, a fifth order stream. These species are abundant in coldwater streams through out the southern Appalachian mountains, the southernmost limit of their range. We collected fishes from Coweeta Creek every second month (between July 1984 and January 1986) and quantified the seasonal reproductive cycles of females, using both histological techniques and the relative gonadal index (RGI). Both techniques indicated that I) C. bairdi reproduced between March and May, 2) CI. funduloides spawned between May and August and 3) R. cataractae were reproductively active between June and July. These conclusions were supported by the following: 1) the presence of reproductive coloration, 2) gravid females, 3) courtship displays, 4) the presence of nest-guarding C. bairdi males and 5) the timing of young-of-the-year recruitment. The reproductive characteristics of these 3 species were correlated with different environmental variables. The mean monthly RGI values for both C. bairdi and R. cataractae were inversely correlated with both maximum and minimum daily water temperatures. The mean RGI values for C. bairdi also were negatively correlated with photoperiod, whereas the values for R. cataractae and CI. funduloides were positively correlated with the change in daily photo period.