D.Litt et Phil. / Please refer to full text to view abstract

Since their introduction to the United States in the 1970s, the invasive silver carp (Hypothalmichthys molitrix) has migrated into the native waters of 16 states with populations in the Mississippi, Missouri, Ohio and Illinois River systems expanding at exponential rates in the past decade. As this species advances towards Lake Michigan, the threat of their invasion into the Laurentian Great Lakes is becoming very real. Silver carp are opportunistic, capable of rapid and extensive dispersal. They have the potential to compete with native species for critical habitat and food, which are very important limiting resources in all freshwater systems. Understanding their diet and habitat selection could be helpful for predicting their expansion and impacts in systems they invade. In order to fully understand habitat selection, 77 silver carp were implanted with ultrasonic transmitters during Spring 2008 and Spring 2009 in Pools 26 (N=24) and 27 (N=53) of the Mississippi River. Fish were located monthly to assess macrohabitat use. To determine if phytoplankton availability was influencing habitat selection, environmental chlorophyll a (used as a surrogate for phytoplankton abundance) was quantified monthly at silver carp detection sites and at randomly generated points from all macrohabitats. 240 silver carp were sacrificed to analyze foregut chlorophyll a concentrations (Pool 26 N=141; Pool 27 N=99); chlorophyll a concentrations in the river at fish locations were measured. This allows us to determine utilization of available phytoplankton resources. Silver carp were detected mostly in channel border wing dike areas with island side channel also being a popular macrohabitat. Chlorophyll a concentrations in the river were higher in areas where carp were detected compared to random sites across all macrohabitat types (Ksa=1.28 p=0.080). There was no significant relationship between foregut chlorophyll a concentrations and what was available in the environment, suggesting silver carp are using resources similarly across all habitats. Given that this species accumulated high concentrations of phytoplankton in their guts even in areas of low phytoplankton concentrations, they may be able to successfully invade areas with scarce phytoplankton resources.

The objective of this thesis was to test the environmental friendly additive substance, in particular sodium caseinate, which is not subject to designation "E" on the label of the product, which is unpopular among the consumers, and which would provide so-called a "higher value" to a product of economically important fish species in the Czech Republic, specifically the common carp (Cyprinus carpio), silver carp (Hypophthalmichthys molitrix) and the rainbow trout (Oncorhynchus mykiss).Determination of the influence of this additive on microbial and biochemical processes, and also on organoleptic properties of the selected smoked fish was another goal of the work. Three concentrations of this product were used for application in total, in particular 25, 50 and 100 g×kg-1. The results of this work confirmed that, due to caseinate (concentration of 100 g×kg-1) such losses of water were avoided, as observed in case of the control group, to which no additive product was applied, and which served for comparison with the groups treated with caseinate. General carp had an average loss of 12.9 % for the samples treated with sodium caseinate and 14 % for the control group. The silver carp white showed similar results. The group treated with caseinate lost 12.4 % in average, and the control group of approximately 14 %. The best results were recorded with the rainbow trout, which, due to caseinate withheld the largest amount of water, respectively, it did not lose so much of weight, in particular 15.9 % for sodium caseinate compared to 19.3 % measured in the control group, however these differences were not confirmed as statistically conclusive. As for the texture of the meat, tougher samples came out for the ones treated with sodium caseinate compared to the more brittle control group. In carp and trout no statistically noteworthy dissimilarity in stiffness of meat was proved between the control group and the group with the applied additive product. While these differences were significant in silver carp. While for silver carp were these differences significant. The control group showed clearly (p<0.05) lower stiffness compared to the group, to which the additive product was applied. Microbiological analysis was performed on the 7th day after smoking, and the values were in the range of 2×10 to 1.9×10^2 CFU×g-1. In the experiment, groups of test fish species did not show any statistically significant difference (p>0.05). Tests for the possible presence of Listeria monocytogenes in all of the smoked fish samples and the control group were negative. Nutrient composition was mainly focused on the basic nutrient components, which were the proteins, fats and carbohydrates. The control group did not show any significant differences compared to the group to which sodium caseinate was applied. The results from the consumers and sensory analysis by a panel of trained persons were very similar. No statistically significant differences between the group treated with caseinate sodium, and the untreated so called control group of smoked species of fish.

Thesis (M. Sc. (Zoology)) -- University of Limpopo, 2015 / The unprecedented expansion in human population and industry, since the industrial revolution in the late 1700s, has led to increased anthropogenic activities which have indisputably impacted freshwater ecosystems and biological communities therein, including fish. Although this has understandably been the focus, under natural aquatic conditions, no organism is only affected by pollution. Parasites have also been shown in a number of interdisciplinary studies to affect the health of aquatic hosts (amphibians, crustaceans, fish, and mammals). This is illustrated in a number of comprehensive studies the detrimental effects parasites exacerbate when their hosts (fish) are stressed. Therefore, the ability of parasites to interact with anthropogenic stressors, as well as effects they have on the genetic, cellular or tissue level of their host is crucial in conservation and sustaining aquatic biodiversity. As such, the present study examined the combined effects of pollution and metazoan parasites on the health and oxidative stress biomarkers, evaluated for the first time for silver carp, Hypophthalmichthys molitrix (Valenciennes, 1844) and rednose mudfish, Labeo rosae Steindachner, 1894, in one of South Africa’s impacted freshwater ecosystems, Flag Boshielo Dam, Olifants River System, Limpopo Province. Seasonal surveys were conducted from February 2012–January 2013. A total of 111 H. molitrix and 116 L. rosae fish specimens were collected using conventional angling gear, scoop and gill nets with stretched mesh sizes of 30–110 mm. The two selected cyprinid fish species were assessed for oxidative stress biomarkers [Glutathione S-transferase (GST), lipid peroxidation (MDA) and Total Antioxidant Capacity (TAC)] and parasitism of metazoan parasites. Concentrations of biomarkers of oxidative damage and antioxidant defense in the gill and liver tissue were measured to assess how these major organs of the immune system responded to oxidative stress associated with parasitic infections. In addition, water quality analyses were carried out by testing an assay of physico-chemical parameters to establish the level of contamination. Fish health was assessed using the Health Assessment Index (HAI), refined Parasite Index (PI), Inverted Parasite Index (IPI) and Condition Factor (K) protocols. Relative to previous studies at Flag Boshielo Dam, water quality results showed an increase of nutrients, major ions and several metals which may have adverse effects that may comprise fish health; however, this dam remains moderately polluted in a mesotrophic state. The fish health assessment results indicated that H. molitrix was more affected in terms of the necropsy and parasite based assessments (HAI, IPI and K) with mean±SD of 65.68±35.51; 68.29±25; 0.82±0.20, respectively, as compared to 39.14±22.44; 28.79±18.33; 1.17±0.21 for L. rosae during the study. In addition, significantly higher parasitic infections (mean prevalence of infection with any species of parasite = 45.3±0.13) were observed for H. molitrix than L. rosae (12.0±0.05). Furthermore, there was considerable variation in biomarker concentration between highly infected and non-infected fish, for and between each species and tissues with regard to parasite infection, suggesting that the specific functions of each tissue are associated with their susceptibility to oxidative stress, as well as their ability to defend against oxidative damage. These results illustrate that although fish are affected by aquatic contaminants they are to an extent affected by parasites, which may act synergistically on the health of the two fish species. Most importantly, it was suggested that knowledge on the parasites of alien H. molitrix when compared to indigenous L. rosae may give an indication of how adaptive this fish are to new localities as well as expands the information on the rarely studied biology, epizootiology and ecological interactions of these two cyprinid species. Keywords: Health Assessment Index, refined Parasite Index, Inverted Parasite Index, Condition Factor, water quality, lipid peroxidation, Glutathione S-transferase, Total Antioxidant Capacity, Hypophthalmichthys molitrix, Labeo rosae, Flag Boshielo Dam.