Hidrobiology

Recommendations and Outlook. Long-term monitoring is required for a better estimation of state and the conditions of Lake Skadar. Further studies on factors influencing the phyto-plankton community, especially zooplankton grazing and toxic substances, which were not included in this study, should be continued in the future to improve the efficiency of phyto-plankton usage in estimating the ecological and trophic conditions of Lake Skadar. Abstract Background, Aims and Scope. Phytoplankton, as a first step in trophic cascades of lakes, can be a good indicator of trophic states, considering that every environmental change affects this community and many species of this community are sensitive to changes, and that they response very quickly. In this study, we tried to assess and predict the trophic state of Lake Skadar according to phytoplankton data. Methods. Water samples were collected using Ruttner sampling bottle. Temperature, dissolved oxygen, ph, conductivity and transparence were measured in situ using portable equipment. Nutrients and chlorophyll a were measured using standard spec-trophotometric methods. A determination of phytoplankton species was performed using relevant keys and the counting of cells was performed using sedimentation methods. Results and Discussion. The species composition of Lake Skadar revealed 95 taxa, with Chlorophyceae and Bacillariophyceae being represented best. According to an average chlorophyll a concentration of 5.9 µg/l, Lake Skadar belongs to the meso-trophic level of the trophic scale. Developed prediction equation for chlorophyll a revealed a good prediction (R 2 =0.71) and the parameter Secchi depth was primarily correlated with chlorophyll a concentration. Trophic state indices derived from chlorophyll a and transparency, were close together, but both were below the phosphorous index. Values of trophic state indices rank the Lake Skadar as being mesotrophic. This study also showed that indices of diversity based on phytoplankton are weak indicators of trophic status and that they can well characterize only differences between assemblages and associations. According to calculated saprobic indices (ranging from 1.5 to 2.15), Lake Skadar is on betamesosaprobic level of saprobity, which means that it is moderately polluted with organic compounds. Conclusions. Total phosphorus is not the main limiting factor for the phytoplankton community in Lake Skadar. Disagreements between chlorophyll and the transparency index, on the one hand, and the total phosphorus index, on the other, suggest that the phytoplankton in Lake Skadar is probably limited by other factors than phosphorus, such as nitrogen, toxic substances or intense zooplankton grazing. According to the majority of investigated parameters and indices derived from phytoplankton data, Lake Skadar is mesotrophic, with tendencies toward eu-trophic levels during the summer period.

In this study, condition factor values, length-weight and length-length relationships of totally 155
Prussian carp, Carassius gibelio (Bloch, 1782) specimens, captured from Lake Ladik between November
2009 and October 2010, were examined. Sex composition was 93.5 % female and 6.5 % male. Fork
lengths of samples ranged from 13.4 cm to 26.5 cm and weights ranged from 58 g to 550 g. Condition
factor values varied between 2.201 and 3.238. Mean condition factor of all individuals was calculated as
2.676. Length-weight relationship was found as W=0.0168L3.149 (r2
=0.988) for all specimens. According
to b value of length-weight relationship, the growth of species was positive allometric (b>3, P<0.001). All
correlations among total length, fork length and standard length were highly significant (P<0.001).

– Qualitative and quantitative phytoplankton compositions of 10 Montenegrin lakes were investigated in the summer of 2007. The obtained results were compared with a previous study-period that was undertaken two decades ago. In the first period, diatoms numerically dominated the phytoplankton community in all studied lakes, while in the second period, the same was observed only in three of the ten lakes; in other studied lakes the relative contributions of green algae, dinoflagellates and/or cyanobacteria increased, while the contribution of diatoms decreased. The shift observed in phy-toplankton composition and diversity in some of the studied lakes indicates an increase in the trophic level over the two decades. The sustainable management plan of the aquatic ecosystems in Montenegro should include the establishment of an environmental monitoring system in order to record any alterations that may take place in water quality.

Phytoplankton seasonal succession and spatial heterogeneity were studied in lake Skadar from February to De-cember 2004. A total of 167 taxa from 6 algal divisions were observed, with Bacillariophyta being best represented (52.8%). The general pattern of phytoplankton seasonal succession in lake Skadar was: Bacillariophyta in the spring, Chlorophyta in early summer, Cyanobacteria and Chlorophyta in late summer and Bacillariophyta and Chlorophyta in autumn and winter. Distinct spatial heterogeneity was observed. The central, open part of the lake (pelagic zone) was characterized by dominant euplanktonic species, mostly diatoms, whereas the western and northwestern parts (more isolated and shallower) had higher abundance of greens and blue-greens and a higher percentage of resuspended benthic-epiphytic forms in the phytoplankton community. Comparison with former phytoplankton data showed distinct differences in terms of the qualitative and quantitative composition of the phytoplankton community of lake Skadar, which indicates lake deterioration .

Background: Since 2011, the coasts of North America, Mexico, and the Caribbean have experienced an
unusual increase in the arrival of Sargassum. As a consequence of this massive accumulations of Sargassum
holopelagic species in Caribbean Sea have been generated and that threaten local biodiversity and trigger
economic losses associated with beach deterioration and impact on fisheries and tourism. Goals: This document quantifies the occurrence of an excessive drift of Sargassum in two sites (Puerto Viejo and Punta Uva) of
the Caribbean coast of Costa Rica, Limón province, in March - April of 2019. A macroalgae species checklist
is presented from six sites (Punta Cahuita, Puerto Vargas, Puerto Viejo, Playa Chiquita, Punta Uva and Manzanillo) in the Caribbean. In addition, the Sargassum morphotypes are quantified for the study area. Methods:
Transects (50 m) were located parallel to the shoreline and, in points previously estimated, a quadrat of 25
x 25 cm covered the entire Sargassum band width on the beach until the water line, by fliping the quadrats
and collecting the biomass for as many quadrats were necessary for the band. Then, pelagic Sargassum
biomass was weighted in every point, and the dry weight biomass was estimated. Three quadrats were
collected by the transect method. Associated species were identified as well as Sargassum morphotypes in
all sites. Results: Descriptions that illustrate the morphology of the three morphotypes of pelagic species.

Phytoplankton seasonal succession and spatial heterogeneity were studied in Lake Skadar from February to December 2004. A total of 167 taxa from 6 algal divisions were observed, with Bacillariophyta being best represented (52.8%). The general pattern of phytoplankton seasonal succession in Lake Skadar was: Bacillariophyta in the spring, Chlorophyta in early summer, Cyanobacteria and Chlorophyta in late summer and Bacillariophyta and Chlorophyta in autumn and winter. Distinct spatial heterogeneity was observed. The central, open part of the lake (pelagic zone) was characterized by dominant euplanktonic species, mostly diatoms, whereas the western and northwestern parts (more isolated and shallower) had higher abundance of greens and blue-greens and a higher percentage of resuspended benthic-epiphytic forms in the phytoplankton community. Comparison with former phytoplankton data showed distinct differences in terms of the qualitative and quantitative composition of the phytoplankton ...

The length–weight relationship, condition factor, sex ratio and fecundity of the Adriatic brown trout, Salmo farioides, were studied in specimens from the upper part of the Morača River during the pre-spawning period. A total of 253 fish were examined; the ratio of matured males to females was estimated as 1:0.5. The length–weight relationship showed a positive allometric growth only in juveniles (age 0+) and isometric growth pattern in the other groups. The absolute fecundity ranged from 137 to 1455 eggs, while the relative fecundity from 210 to 596 (mean 310.89) eggs per 100 grams of body weight. The minimum size at first sexual maturity was 13.7 cm total length in females, and 11.4 cm total length in males. Estimates of the average K ranged from 1.03 in juveniles 0+, to 1.10 in mature males.

The relationships between size (length and width) of the lagenar (asteriscus) and the utricular (lapillus) otoliths and body
length for five cyprinid fish species, freshwater bream Abramis brama, white bream Blicca bjoerkna, Prussian carp Carassius gibelio, brond-snout Chondrostoma regium, and rudd Scardinius erythrophthalmus, collected from Lake Ladik from November 2009 through October 2010, are presented. The right and left side measurements of otoliths were pooled in all cases except asteriscus length in Prussian carp. Nonlinear and linear functions provided the best fit for 80% and 20% of all species, respectively. All relationships were
highly significant (P < 0.001, R2 > 0.71) and the mean percent prediction errors were less than 10%. The results showed that reliable original size estimates of all species studied are obtainable from their otolith biometrics. The regressions from this study can be useful for investigators examining food habits of piscivorous fauna and sizes of these fishes in archaeological samples.