Comparison of Zn, Cu, Pb, Ni, Cr, Sn, Mo Concentrations in Tissues of Fish (Roach and Perch) from Lake Baikal and Bratsk reservoir, Russia

Data on Zn, Cu, Pb, Ni, Cr, Sn, Mo concentrations in some food fish in Baikal Lake and Bratsk reservoir have been compared. The muscles, skin and gills of roach and perch (Rutilus rutilus and Perca fluviatis L.) were analysed. The conditions of atomic-emission analysis, detection limits, reproducibility, coefficients of transformation from the wet to dry mass and to an ash residue are reported. To verify accuracy, the results of reference samples OK-1 (Baikal perch) and OM-1 (Baikal roach) were used along with atomic-absorption and neutron-activation results of ashed and dried samples. The observed range of concentrations in tissues exceeds the probable analytical errors and reflects natural variability. The content of Zn, Cu, Pb, Ni and Cr in tissues of fish collected in the Bratsk reservoir from the conventionally uncontaminated and polluted sites correspond to the concentrations in tissues of similar fish from Lake Baikal. The latter are normal for fish of weakly mineralised oligotrophic reservoirs. The ranges of concentration in studied fish (roach and perch) consist of mg kg^–1 dry wt: in muscles-Zn(14–28), Cu(2.2–4.7), Pb(0.30–0.61); in skin-Zn(94–119), Cu(1.2–1.4), Pb(0.16–0.08); in gills-Zn(70–280), Cu(2.0–7.4), Pb(0.19–1.2).     

Ontogenetic changes in the retinal topography of the European hake, Merluccius merluccius: implications for feeding and depth distribution

Changes in the distribution pattern of cells in the ganglion cell layer were studied in the retina of the European hake, Merluccius merluccius (L.), to identify the possible adaptations of visual capabilities to different bathymetric distributions and feeding habits. From early juveniles to adults, the eye diameter increased eightfold; thus, retinal surface increased dramatically with size also. In early juveniles the retinal topography of the cells in the ganglion cell layer showed a concentric arrangement with respect to the centre of the retina. Two specialised areas were found, located at the ventral and dorso-rostral periphery, where the cell density reached 47,900 cells mm^-2, which corresponds to a theoretical visual acuity of 21' (minutes of arc). The visual axes were located upwards and downwards at around 80° from the geometric centre of the retina. In juveniles, the retina underwent important changes as the concentric topographic pattern transformed: the ventral specialised area progressively disappeared, the dorso-rostral area relocated to a rostral position and a new specialised area formed in the temporal retinal region. The visual axes were directed forward and backward. For fish with a total length of 12 cm or more, a horizontal visual streak formed along the rostro-temporal axis of the retina and a new specialised area was formed in the temporo-central region of the visual streak. In adults, acute vision could be identified with the two specialised areas at the temporal and rostral periphery, where the ganglion cell density peak decreased to 3,200-3,600 cells mm^-2 and the resolving power increased to 10'. As visual acuity is partially dependent on the cell types in the ganglion cell layer, cell populations in this layer were distinguished into either ganglion cells or displaced amacrine cells, using morphometric and histological criteria. The proportion of displaced amacrine cells was fairly uniform throughout the retinal surface, always representing between 32% and 39% of all cells in early and advanced juveniles. Only in adults did their density increase to 50%, probably as an adaptation to low light levels, which fish encounter as their distribution increases in depth. A small population of giant ganglion cells was also present in the retina. In the young and adult retinae, they represented 1.2% and 2.7% of the total cell population, respectively. Therefore, it has been shown how in M. merluccius the retinal topography undergoes important changes in relation to varying environmental demands.     

Ichthyofaunas of a temperate estuary and adjacent marine embayment. Implications regarding choice of nursery area and influence of environmental changes

A fine-mesh seine net was used at regular intervals to collect fishes from the entrance channel and basin of the Blackwood River Estuary (south-western Australia), from Deadwater Lagoon, which is joined to the entrance channel by a narrow and shallow water-course and thus constitutes part of this estuary, and from Flinders Bay into which the estuary discharges. Sampling was at six-weekly intervals between February and December 1994. The juveniles of some marine species, such as Pelates sexlineatus, Rhabdosargus sarba and Aldrichetta forsteri, were either found only in the estuary or were in far higher densities in the estuary than in Flinders Bay. In contrast, the juveniles of some other marine species, such as Sillago schomburgkii, were relatively abundant in both environments, while others such as S. bassensis, Pelsartia humeralis, Lesueurina platycephala and Spratelloides robustus were either far more abundant in Flinders Bay or entirely restricted to this marine embayment. The various marine species found in inshore waters thus apparently vary considerably in their “preference” for estuaries as nursery areas. Although some marine species were abundant in the shallows of the estuary, the fish fauna of these waters was dominated by the estuarine-spawning species Leptatherina wallacei, Favonigobius lateralis, L. presbyteroides and Atherinosoma elongata. The above regional differences help account␣for the very marked difference that was found between the compositions of the shallow-water␣ichthyofaunas of Flinders Bay and each of the three estuarine regions. The ichthyofaunal compositions of the basin and channel underwent pronounced changes during winter, when freshwater discharge increased markedly and salinities in the estuary thus declined precipitously. This faunal change was mainly attributable to the emigration of marine stragglers, a reduction in the densities of marine estuarine-opportunist species such as Pelates sexlineatus and R. sarba, and the immigration of large numbers of both young 0+ Aldrichetti forsteri from the sea and of L. wallacei from the river. Although most of the above species were also abundant in Deadwater Lagoon, the ichthyofaunal composition of this region did not undergo the same seasonal changes, presumably due to the lack of riverine input and thus the maintenance of relatively high salinities throughout the year. The number of marine straggler species was much lower in Deadwater Lagoon than in the estuary basin, reflecting a far more restricted tidal exchange with the entrance channel. However, the overall density of fishes was far higher in Deadwater Lagoon than in the estuary basin or entrance channel, due mainly to the far higher densities of the estuarine species Atherinosoma elongata and L. wallacei and of the 0+ age class of the marine species R. sarba. The high densities of certain species in Deadwater Lagoon are assumed to be related, at least in part, to the high level of productivity and protection that is provided by the presence of patches of Ruppia megacarpa, an aquatic angiosperm that was not present in the estuary basin or entrance channel. Received: 3 December 1996 / Accepted: 19 December 1996     

Reproductive biology of the red alga Polysiphonia lanosa (Ceramiales) in the Bay of Fundy, Canada

The purpose of this investigation was to establish reproductive phenology of the dioecious marine floridean red alga Polysiphonia lanosa (L.) Tandy. Specifically, the distribution and frequencies of male and female plants, timing of their sexual maturity, fecundity and success of fertilization were investigated. The presence of cystocarps was taken as an indication of syngamy. Populations of P. lanosa in the Bay of Fundy reproduce in spring, summer and autumn. Both male and female filaments were present in equal abundance at all sampling locations, grew in close proximity, and occurred with equal abundance at all elevations above chart datum. During the growing season most of the mature plants contained reproductive organs with apparently functional gametangia containing gametes the structure and behavior of which conformed to those reported in the literature for other species of the genus. Male and female plants of P. lanosa matured synchronously during late May to early July at all collecting sites. The ratio of spermatia to carpogonia calculated for the sampled population was high, 3000–4800 spermatia:1 carpogonium. At the end of the growing season (late October) the fertilization success was at its maximum of 50 to 90% and at its minimum in July at 24%. The three free-living life-history phases (females, males and tetrasporophytes) were abundant and occurred with equal frequency, indicating that a complete life cycle was common at the studied location. Received: 10 December 1996 / Accepted: 16 January 1997     

Do protandric pandalid shrimp have environmental sex determination?

Based on demographic analysis of four different temporally enclosed demes of Pandalus borealis in Gullmarsfjorden on the Swedish west coast and published information, I discuss the notion of environmental sex determination in protandric pandalid shrimps as suggested by sex allocation theory. Demographic results showed that age structure and mortality rates varied substantially between four studied periods without noticeable effects on the age of sex change in the fjord populations. The majority of shrimps changed sex at an approximate age of 3 years and became females at an age of 3 to 4 years, however, low proportions (4 to 7%) of 2nd year females (transitional at ca. 1 year) and 3rd year females (5 to 12%) (transitional at ca. 2 years) were present each year. Low proportions of primary females were also found in two of the temporally enclosed demes, in 1985 (9%) and in 1987 (5%). These results do not indicate that yearly variations in age structure, mortality, or frequency of older breeders in the breeding population affect the age of sex change in temporally enclosed fjord demes of this protandric species. An alternative to assuming that the protandric mode of reproduction in pandalid shrimp is combined with environmental sex determination is suggested. Received: 24 September 1996 / Accepted: 6 November 1996     

Divorce in common murres (Uria aalge): relationship to parental quality

Behavioral precursors of 12 divorces were examined in 30 color-banded pairs of common murres (Uria aalge) over six breeding seasons. Common murres are long-lived seabirds that typically return each year to the same mate and nest site in dense colonies. At least one parent is present continuously from egg lay to chick fledging. Murres, therefore, have considerable opportunities to compare their mates parental behavior with that of several familiar neighbors. Previous reproductive success was lower for divorcing birds than for reuniting pairs. As predicted by the better option hypothesis, there were clear choosers (seven females and five males) that initiated divorce by moving to a new birds site or by courting a new partner at their current site. Choosers improved their reproductive success after the divorce, whereas their previous partners, the victims did not. Yearly divorce rates (average 8.2% per year) were significantly correlated with yearly mortality rates. Divorces appear to be opportunistic: pairs divorced after varying numbers of reproductive failures with the immediate precursor usually being the disappearance (death) of a murre from a successful neighboring site. In contrast to the delays experienced by victims, choosers formed new pairs quickly and laid their eggs no later than reuniting pairs. Prior to the divorce, victims fed their chicks less often than choosers, and some engaged in other behaviors that compromised egg or chick survival. These observations suggest that deficiencies in parental behavior were precursors to the divorce. This report is one of the first cases where reproductive failure of divorcing pairs has been linked to deficits in the parental behavior of the subsequent divorce victim.Communicated by C. Brown     

Concentrations of inorganic elements in bottled waters on the Swedish market

This study presents the concentrations of about 50 metals and ions in 33 different brands of bottled waters on the Swedish market. Ten of the brands showed calcium (Ca) concentrations ≤10 mg L⁻¹ and magnesium (Mg) levels <3 mg L⁻¹, implying very soft waters. Three of these waters had in addition low concentrations of sodium (Na; <7 mg L⁻¹), potassium (K; <3 mg L⁻¹) and bicarbonate (HCO₃ ≤31 mg L⁻¹). These brands were collected from barren districts. Nine of the brands were collected from limestone regions. They showed increased Ca-levels exceeding 50 mg L⁻¹ with a maximum of 289 mg L⁻¹. Corresponding Mg-levels were also raised in two brands exceeding 90 mg L⁻¹. Two soft and carbonated waters were supplemented with Na₂CO₃ and NaCl, resulting in high concentrations of Na (644 and 648 mg L⁻¹) and chloride (Cl; 204 and 219 mg L⁻¹). Such waters may make a substantial contribution to the daily intake of NaCl in high water consumers. The storage of carbonated drinking water in aluminum (Al) cans increased the Al-concentration to about 70 μg L⁻¹. Conclusion As there was a large variation in the material as regards concentrations of macro-elements such as Ca, Mg, Na, K and Cl. Supplementation with salts, e.g., Na₂CO₃, K₂ CO₃ and NaCl, can lead to increased concentrations of Na, K and Cl, as well as decreased ratios of Ca/Na and larger ratios of Na/K. Water with high concentrations of e.g., Ca and Mg, may make a substantial contribution to the daily intake of these elements in high water consumers. Al cans are less suited for storage of carbonated waters, as the lowered pH-values may dissolve Al. The levels of potentially toxic metals in the studied brands were generally low.     

Condition-specific competition in container mosquitoes: the role of noncompeting life-history stages

Condition-specific competition, wherein competitive superiority varies with the abiotic environment, can determine species' distributions in a spatially heterogeneous environment. We investigated this phenomenon with two competing container-dwelling mosquitoes. We tested the hypothesis that habitat drying alters the outcome of interspecific competition, predicting that the competitive impact of Aedes albopictus on Aedes aegypti would be severe in wetter environments, but greatly reduced in drier environments. We tested these predictions in a laboratory experiment within cages, with aquatic larvae residing in water-filled cups within the cage, and adults emerging within the cage and ovipositing on the cups. We raised each species alone or with the competitor. Environmental treatments were fluctuating (water in cups evaporated to 50% of the original volume and then cups were refilled), and drying (water in cups evaporated completely and cups remained dry for two weeks before refilling). There was a significant interaction between treatment and species combination for adult populations of both species. Interspecific competition was highly asymmetrical. In the wetter fluctuating environment, interspecific competition had a large negative effect on A. aegypti, but in the drying environment, interspecific competition had a large negative effect on A. albopictus, and relatively little impact on A. aegypti. The main cause of the shift in competitive advantage appeared to be a greater increase in egg mortality for A. albopictus under dry conditions, compared to A. aegypti. Thus, mortality impinging on noncompeting life cycle stages can alter the population level impact of interspecific competition. The hypothesis that dry conditions shift competitive advantage away from A. albopictus is supported in this experiment.