Harvest Rates of Rheophilic Fish Vimba vimba, Chondrostoma nasus, and Barbus barbus Have a Strong Relationship with Restocking Rates and Harvest Rates of Their Predator Silurus glanis in Lowland Mesotrophic Rivers in Central Europe

The European catfish Silurus glanis (Linnaeus, 1758) is an expanding apex piscivorous predator whose predation may drive fish harvest rates and fish populations. This study aimed to analyze the relationships between intensive catfish stocking/harvesting and harvest rates of putative catfish prey–three rheophilic fish species: vimba bream Vimba vimba, nase Chondrostoma nasus, and barbel Barbus barbus (Linnaeus, 1758). The GAM (generalized additive model) was used to analyze the relationships between the harvest rate and the stocking intensity rate of the catfish and the three rheophilic fish species. The harvest rates and stocking intensity rates were obtained from mandatory angling logbooks collected from 38,000 individual recreational anglers by the Czech Fishing Union on 176 fishing sites over the years 2005–2017 in central Bohemia and Prague (the Czech Republic). Our results show that a higher intensity of catfish stocking and harvesting resulted in a lower harvest rate of rheophilic fishes. Conversely, the stocking rates of rheophilic fishes were not significantly correlated to their harvest rates. In conclusion, a significant negative relationship was found between the harvest rate and the restocking rates of rheophilic fishes and their predator, suggesting that fisheries managers should not perform intensive stocking of both catfish and rheophilic fishes on the same rivers.

A new method for measuring fish swimming patterns in shallow water and a previously undescribed swimming gait

Hill stream loaches are fish which live their entire lives in close contact with rock. They have elaborate physical adaptations to fast flow, adherence to substrate, and movement in very shallow water. Here we describe a method for observing how they swim in detail. There are many similarly shaped rheophilic fish, insects, and amphibian larvae, which live in fast flowing water, and a method of observing their swimming modes has wide potential application. We measured the deflection of the water surface around a swimming fish by viewing a fixed pattern on the bottom of the tank through the water surface. This is a Schlieren method in which the movement or other physical properties of a medium are derived from the deflection of a pattern viewed through that medium. We used this method to describe a new type of swimming gait which is likely to be common among small rheophiles – pulse swimming mode – in which thrust is produced in a series of discrete impulses. The method of analysis described here is beneficial in that the fish is allowed to swim freely in relatively normal conditions without the use of intrusive equipment such as lasers, dyes, or additives to the water, and the pattern of thrust is viewed directly against the skin of the fish rather than being inferred from the wake pattern behind the fish. The method is also low cost and easily set up.

SEASONAL VARIATION IN SEMINAL QUALITY IN BRAZILIAN BOCACHICO (TELEOSTEI, CHARACIFORMES)

ABSTRACT The Brazilian bocachico, Prochilodus brevis, is a rheophilic fish. Although there is evidence that this species shows reproductive seasonality in the wild, in captivity hormonal induction techniques allow semen sampling in different seasons. This study aimed to compare the kinetics, morphology and biochemical composition of the semen of Brazilian bocachico in captivity when hormonally induced to breed in the reproductive and non-reproductive seasons. During sampling spermiation was hormonally induced in breeders. The concentrations of total protein, glucose, fructose, triglyceride, calcium and chloride were evaluated with biochemical kits. The pH data (6.5 to 8.5) suggest semen requires alkaline conditions, as expected for freshwater fish. Seminal plasma contained more protein (1.51 ± 0.06 dL g-1), glucose (79.44 ± 1.88 mg dL-1) and triglycerides (61.59 ± 8.10 mg dL-1) in the non-reproductive than the reproductive season, but calcium ions (15.98 ± 1.02 mg dL-1) showed the opposite pattern. There was a significant seasonal difference in sperm morphology, with a higher percentage of normal sperm in the reproductive season. From these data it can be concluded that the physical, kinetic, morphological and biochemical characteristics of semen of captive Prochilodus brevis are influenced by reproductive season.

Influence of Cooling Time and Diluents on the Freezability of Prochilodus brevis semen

Background: Prochilodus brevis is a rheophilic fish of economic and ecological importance. However, anthropic action has made its population vulnerable. Thus, the development of reproductive biotechnologies, such as seminal conservation, is necessary to subsidize their fish farming. However, seminal collections are often performed in places with few laboratory resources, demanding studies to determine the maximum time for which sperm can be cooled, as well as its process until frozen. Thus, the present study aimed to evaluate the influence of cooling time and the presence of dilution solutions on cryopreservation of P. brevis semen.Material, Methods & Results: After seminal collection, nine pools were formed and analyzed for seminal pH, concentration, membrane integrity, morphology and spermatic kinetics - motility, curvilinear velocity (VCL), average path velocity (VAP) and straight line velocity (VSL). After the analysis of the pools in natura (control 1), they were processed as follows: 1)- immediate freezing (control 2); 2)- cooling: undiluted, diluted in coconut water powder (ACP-104) or diluted in 5% glucose, followed by cooling at different times (6, 12, 24 or 48 h); 3)- Post-refrigeration freezing: the pools were diluted in their respective diluents and 10% dimethyl sulfoxide. After 15 days, the samples were thawed and analyzed for the aforementioned parameters. For the cooled and post-thawed semen, a completely randomized design with 2 (diluent × cooling time) and 3 (storage form × cooling time and storage form × diluent) factors, respectively, was utilized. ANOVA and Dunnett tests were applied to compare the means. In case of seminal cooling, there was no difference (P > 0.05) in sperm motility between control 1 and the undiluted and diluted treatments in ACP-104 for up to 24 h. After 48 h, only the VCL of the sample diluted in ACP-104 was similar (P > 0.05) to that of control 1. When comparing forms of storage (undiluted, diluted in ACP-104 or diluted in glucose) and cooling times, the undiluted samples and the samples diluted in ACP-104 were better (P < 0.05) for all the kinetics parameters analyzed, than those diluted in glucose after 24 h. After 48 h, the cooled semen diluted in ACP-104 presented greater (P < 0.05) motility than the other treated semen samples. The samples diluted in glucose for 48 h presented lower spermatic velocity (P < 0.05) than those subjected to other treatments. Regardless of the diluent used, the post-thawed semen and the cooled semen diluted for 6 h, presented higher sperm kinetic values (P < 0.05) than those of control 2 and other treated samples. Overall, the samples diluted in ACP-104 showed satisfactory results when cooled for up to 48 h or cooled for up to 6 h and frozen.Discussion: This is the first study that froze semen from P. brevis after cooling. Although glucose is a commonly used diluent during seminal freezing and has good post-thawing stability for this species, it is not recommended for cooling before seminal freezing, as prolonged exposure of spermatozoa to glucose may cause osmotic stress to sperm cells. Conversely, good results with ACP-104 might be because of its rich composition, mainly the presence of indole-3-acetic acid (IAA), an auxin with proven potential for seminal conservation of other species. Therefore, for fertilization trials, it is recommended to use ACP-104 as diluent for seminal cooling of P. brevis for up to 48 h or semen that has been frozen after cooling in ACP-104 for a maximum of 6 h.

Rheophilic fish in oxbow lakes of the Warta River – the effect of environmental conditions on habitat selection

Oxbow lakes are typical elements of meandering watercourses and are considered to be key components of floodplains of natural rivers. A permanent connection with the river promotes the use of these water bodies by ichthyofauna as spawning grounds, shelter for fry, feeding and wintering grounds. The aim of this study was to determine which rheophilic species inhabit oxbow lakes and how environmental conditions affect habitat selection and fish behavior. Analyses were conducted on six oxbow lakes of the Warta River in the Koło-Poznań section. Fish and water samples were collected for three years, in spring, summer and late autumn. Variation in environmental conditions in the analyzed water bodies results in a considerable diversity of the ichthyofauna, including rheophilic species, in individual seasons of the year. In the course of the study, nine rheophilic fish species were recorded, including four from the lithophilic reproductive guild having the highest environmental requirements. Relative abundance of rheophilic species in the dominance structure ranged from 0 to 100%, depending on the reservoir and seasons, with an average of 7% for all catches. For comparison, their relative abundance in the adjacent parts of the river was 12 and 23%.