Describing and simulating phytoplankton of a small and shallow reservoir using decision trees and rule-based models.

Phytoplankton represents one of the most important biological components of primary production, trophic interactions, and circulation of organic matter in lakes and reservoirs. To contribute to the understanding of eutrophication processes and ecological status of the small, shallow Butoniga reservoir, a machine learning tool for induction of models in form of decision trees and rule-based models was applied on a dataset comprising physical, chemical, and biological variables measured at four stations. Two types of models were successfully elaborated, i.e., (1) model describing phytoplankton Phylum, which describes and connects phytoplankton Phylum with phytoplankton abundance and biomass, and (2) model simulating phytoplankton biomass according to environmental variables which could be used in management purposes. Such models and their presentation contribute to a better understanding of the Butoniga reservoir ecosystem functioning.

Correlation between acoustic divergence and phylogenetic distance in soniferous European gobiids (Gobiidae; Gobius lineage).

In fish, species identity can be encoded by sounds, which have been thoroughly investigated in European gobiids (Gobiidae, Gobius lineage). Recent evolutionary studies suggest that deterministic and/or stochastic forces could generate acoustic differences among related animal species, though this has not been investigated in any teleost group to date. In the present comparative study, we analysed the sounds from nine soniferous gobiids and quantitatively assessed their acoustic variability. Our interspecific acoustic study, incorporating for the first time the representative acoustic signals from the majority of soniferous gobiids, suggested that their sounds are truly species-specific (92% of sounds correctly classified into exact species) and each taxon possesses a unique set of spectro-temporal variables. In addition, we reconstructed phylogenetic relationships from a concatenated molecular dataset consisting of multiple molecular markers to track the evolution of acoustic signals in soniferous gobiids. The results of this study indicated that the genus Padogobius is polyphyletic, since P. nigricans was nested within the Ponto-Caspian clade, while the congeneric P. bonelli turned out to be a sister taxon to the remaining investigated soniferous species. Lastly, by extracting the acoustic and genetic distance matrices, sound variability and genetic distance were correlated for the first time to assess whether sound evolution follows a similar phylogenetic pattern. The positive correlation between the sound variability and genetic distance obtained here emphasizes that certain acoustic features from representative sounds could carry the phylogenetic signal in soniferous gobiids. Our study was the first attempt to evaluate the mutual relationship between acoustic variation and genetic divergence in any teleost fish.

Loaches in a long term study of the Drava River in Croatia.

The diversity, species composition and structure of the fish community were studied in the vicinity of three power plant reservoirs in the middle part of the Drava River in Croatia. Over a period of twenty years in a collection of 25,913 fishes, 56 different fish species belonging to 16 families were recorded. The family Cobitidae is represented by two species: Cobitis elongatoides and Misgurnus fossilis, while the family Balitoridae is represented by only one species, Barbatula barbatula. The presence of the Cobitidae family was recorded in eleven of seventeen investigated localities, while Balitoridae was found in six localities. In the studied fish community, the percentage of C. elongatoides is 1.41% of the total number of individuals, and B. harbatula is 1.02%. M. fossilis is a rare species (0.03 %). Both C. elongatoides and B. barbatula were not caught at the beginning of investigation. C. elongatoides and B. harhatula were first caught in 1985, while M. fossilis was first caught in 1996. The proportion of C. elongatoides in the entire community increased, while the proportion of B. barhatula decreased in later years.

Growth of Cobitis narentana Karaman, 1928 in the Neretva River, Croatia.

Age and growth of Cobitis narentana were examined in the delta of Neretva River in Croatia. Maximum observed length was 100.4 mm for females and 63.5 for males. Five age classes were determined, from 0+ to 4+. For both females (61.0%) and males (53.8%), the greatest proportion of specimens were in the 1+ age category. Growth was faster in males in the first year of life, while females grew at a faster rate than males after the first year. The Fulton condition factor was determined (CF=0.588 for males and CF=0.618 for females). The length-weight relationship was determined for females (W=8xl0(-5)L2.9325) and males (W=2x l0(-5)L2.6431). The parameter b was calculated as less than b=3.0, thus establishing that growth in both males and females was allometric. Growth rate was determined using the von Bertalanffy growth rate curves for females (Lt=101.1[ 1-e(-0.5(t-0.94)]; r2=0.99) and for males (Lt=65.3[1-e(-0.54(t-2.27)]; r2=0.97). The resulting growth rate coefficient (K) was found to be slightly higher in males (0.54) than in females (0.5).