The diet of reservoir perch before, during and after establishment of non-native tubenose goby

In recent decades, gobiid species have increased their distribution throughout Europe and now often represent the dominant genus along many rivers and canals. In this study, we assessed the role of tubenose goby (Proterorhinus semilunaris) as a prey species of native perch (Perca fluviatilis) in a lowland reservoir soon after their initial introduction in 1994 (sampling started 1998) and 17 years after establishment (2011–2012). We compare these data with perch diet composition from before introduction (1981–1982). Our data indicate that tubenose gobies quickly became the dominant species along the reservoir bankside, making them an attractive prey for ≥1 + perch. There was a clear increasing trend in the numbers of larger perch caught along the rip-rap, with the largest fish clearly specialising on gobies. As such, introduction of tubenose gobies has had a pronounced effect on food web and population dynamics along the littoral zone. While goby numbers appear to have dropped significantly in recent years, apparently due to predation pressure, further studies are needed to assess whether such changes have had any general impact on population and food web dynamics within the reservoir

Gobiidae - food competitors for our native fish species?

To date, two species of the non-native Gobiidae family have been recorded in the Czech Republic: the tubenose goby (Proterorhinus semilunaris) and round goby (Neogobius melanostomus). The aim of this study was to assess the dietary habits of these two species, with the relationship between goby diet and that of native species (potential competition, predation) of particular interest. Early results suggest that the main dietary items of both gobiids are common benthic invertebrates such as Chironomidae, Trichoptera and Ephemeroptera. Fish eggs and fry were rarely taken by either species and, when taken, consisted almost exclusively of eggs and fry of their own species (cannibalism). In addition, the round goby was shown to be necrophagous, scavenging on large fish carcasses. This behaviour si relatively rare in the Czech fish assemblage. Our results suggest that tubenose and round goby, while not predating heavily on native benthivorous species, may still represent possible competitors

Brewer’s yeast as a diet supplement in carp aquaculture: impact on production coefficients and haematological and biochemical plasma parameters

While brewer’s yeast (Saccharomyces cerevisiae), a rich source of proteins and B vitamins, is commonly used as an animal feed supplement, its use in aquaculture has been limited. Here, we assess its impact on 192 individuals of common carp (Cyprinus carpio) production and haematological and biochemical parameters from blood plasma using a control group fed commercial feed with 20% soybean meal and three test groups fed commercial feed with (i) 17.50% soybean + 2.50% brewer’s yeast (group B-2.5), (ii) 15% soybean + 5% yeast (group B-5) and (iii) 10% soybean and 10% yeast (group B-10). At the end of the experiment, all fish were weighed and measured and subsequently blood samples were taken from eight fish in each tank. There was a significant increase in total length (3%) and weight (5.37%) in group B-5. While fish muscle nitrogenous matter and protein efficiency ratio increased slowly across experimental groups, Fulton’s and Clark’s condition factors changed minimally (range 2.73–2.89%). Apparent net protein utilisation increased to 17.63% in B-10, suggesting that increasing yeast levels result in improved nitrogen utilisation. All fish muscle fat levels were within optimal range (4.16–4.68%) and, while there was a significant increase in erythrocytes in B-5 (up 0.40 T.L−1), haemoglobin levels increased only slightly in B-5 and B-10 (average 4.50 g.L−1) and B-10 had the lowest number of leukocytes (6.8 G.L−1). No significant changes were recorded in blood plasma biochemical parameters. Our results suggest that a 5% brewer’s yeast feed supplement represents a useful protein source for carp aquaculture

The diet of reservoir perch before, during and after establishment of non-native tubenose goby

In recent decades, gobiid species have increased their distribution throughout Europe and now often represent the dominant genus along many rivers and canals. In this study, we assessed the role of tubenose goby (Proterorhinus semilunaris) as a prey species of native perch (Perca fluviatilis) in a lowland reservoir soon after their initial introduction in 1994 (sampling started 1998) and 17 years after establishment (2011–2012). We compare these data with perch diet composition from before introduction (1981–1982). Our data indicate that tubenose gobies quickly became the dominant species along the reservoir bankside, making them an attractive prey for ≥1 + perch. There was a clear increasing trend in the numbers of larger perch caught along the rip-rap, with the largest fish clearly specialising on gobies. As such, introduction of tubenose gobies has had a pronounced effect on food web and population dynamics along the littoral zone. While goby numbers appear to have dropped significantly in recent years, apparently due to predation pressure, further studies are needed to assess whether such changes have had any general impact on population and food web dynamics within the reservoir

The diet of reservoir perch before, during and after establishment of non-native tubenose goby

In recent decades, gobiid species have increased their distribution throughout Europe and now often represent the dominant genus along many rivers and canals. In this study, we assessed the role of tubenose goby (Proterorhinus semilunaris) as a prey species of native perch (Perca fluviatilis) in a lowland reservoir soon after their initial introduction in 1994 (sampling started 1998) and 17 years after establishment (2011–2012). We compare these data with perch diet composition from before introduction (1981–1982). Our data indicate that tubenose gobies quickly became the dominant species along the reservoir bankside, making them an attractive prey for ≥1 + perch. There was a clear increasing trend in the numbers of larger perch caught along the rip-rap, with the largest fish clearly specialising on gobies. As such, introduction of tubenose gobies has had a pronounced effect on food web and population dynamics along the littoral zone. While goby numbers appear to have dropped significantly in recent years, apparently due to predation pressure, further studies are needed to assess whether such changes have had any general impact on population and food web dynamics within the reservoir