Variability of the countable features of head seismosensory system in different species of freshwater fishes and their dependence on hydrochemical factors

Countable morphological features in individuals of three mass species of fishes – roach, perch and crucian carp, living in small ponds of the Central-Eastern part of Udmurtia – were studied. The number of holes of seismosensory channels in some paired cover bones of the head skeleton of the caught fishes was counted and the sum of the values of these countable features (ΣSS) was calculated with averaging for the left and right sides. The total mineralization of water was also measured in the investigated reservoirs and the content of calcium and magnesium ions was estimated in the water. For all three fish species, one trend of interpopulation variability was revealed: with an increase of the concentration of Mg2+ in fresh water, the average value of ΣSS decreased in fish individuals from the studied populations. Statistically significant differences in mean values and frequency distributions of discrete variants of this seismosensory feature were observed for populations of roach, perch and crucian carp, living in water bodies with the greatest differences in the content of magnesium. In addition to full-scale research, laboratory experiments on aquarium cultivation of juvenile perch and roach in various hydrochemical conditions were carried out. Formed in fresh water with a high content of Mg2+, perch and roach juveniles had a smaller number of holes of seismosensory channels in some head bones in comparison with juveniles from the control groups and adult individuals of these fish species in reservoirs, where fertilized fish eggs for incubation were taken. Increased concentrations of Na+ did not have a similar effect on the formation of the studied signs. To explain the observed ontogenetic effects, we consider the possibility of direct influence of magnesium ions on the rate of larvae development of the freshwater fishes, as well as indirect influence on their morphogenesis of the competitive biochemical relations of this element with calcium.

Variations of Salminus hilarii diet (Ostariophysi, Characidae): seasonal and ontogenetic effects

This study described the variations seasonal and ontogenetic of Salminus hilarii diet. Samples were collected in the Sorocaba River, São Paulo, Brazil, one of the few rivers where individuals of the species still occur in a higher frequency. The preys consumed were analyzed by Importance Alimentary Index (AIi). To determine similarities between year seasons, the AIi data were analyzed by the Morisita-Horn index and reduced in cluster analysis, along with a statistical comparison made by one-way ANOSIM test (5%). The feeding activity was analyzed according to the stomach repletion index and compared among the year seasons using non parametric variance analysis Kruskal-Wallis test (5%). Comparison of prey consumed between immature and adult individuals was made by Spearman correlation (5%). A Pearson correlation (5%) was applied between the standard length of the fish and prey consumed, as well as between the mouth and prey heights. The analyzes of stomach contents showed that the diet of this species was exclusively piscivorous, with significant difference of prey consumption during the period, the same happening among adult and immature individuals. It was observed that these fishes use to swallow their prey whole and that significant correlations between size of predator and prey size can be observed. There is also correlation between the mouth height and the maximum prey depth. Salminus hilarii feeds on the available prey, and the species food composition and feeding activity depends on prey`s abundance, their size and morphology, as do the water temperatures.

The B/Ca proxy for past seawater carbonate chemistry reconstructions-laser ablation based calibrations for <i>C. mundulus</i>, <i>C. wuellerstorfi</i> and its morphotype <i>C. cf. wuellerstorfi</i>

B/Ca ratios in Cibicides mundulus and Cibicides wuellerstorfi have been shown to correlate with the degree of calcite saturation in seawater (Δ[CO32−]). In the South Pacific, a region of high importance in the global carbon cycle, these species are not continuously present in down-core records. Small numbers of epibenthic foraminifera in samples present an additional challenge, which can be overcome by using laser ablation-inductively coupled-mass spectrometry (LA-ICP-MS). We present a laser ablation based core-top calibration for Cibicides cf. wuellerstorfi, a C. wuellerstorfi morphotype that is abundant in the South Pacific and extend the existing global core top calibration for C. mundulus and C. wuellerstorfi to this region. B/Ca in C. cf. wuellerstorfi are linearly correlated with Δ[CO32−] and possibly display a higher sensitivity to calcite saturation changes than C. wuellerstorfi. Trace element profiles through C. wuellerstorfi and C. mundulus reveal an intra-shell B/Ca variation of ±36% around the mean shell value. Mg/Ca and B/Ca display opposite trends along the shell. Both phenomena likely result from ontogenetic effects. Intra-shell variability equals intra-sample variability, mean sample B/Ca values can thus be reliably calculated from averaged spot results of single specimen. In the global B/Ca–Δ[CO32−] range, we observe an inverse relationship between water mass age and Δ[CO32−].