Parasites and non-fish predators of tilapia with particular reference to the sustainable management of fisheries of Lake Kainji Nigeria

The fisheries of Lake Kainji, Nigeria, experienced a boom year following impoundment, then decline post impoundment and now is in a period of stabilisation of the fish resources. Several reasons have been advanced on factors responsible for these changes, but two outstanding factors are those of nutritional status and fishing methods of the lake. Two important fish families however continue to dominate the lake fisheries in daily fisherman catches: Clupeidae and Cichlidae (tilapias). Recent studies have also shown that the dominance of the tilapias and clupeids is an important factor in the understanding of the stability of fisheries of Lake Kainji. One area which has remained undiscussed concerns the parasites and non-fish predators of tilapias which can affect the population dynamics of tilapias. This paper examines therefore some aspects of the fisheries of Lake Kainji and the potential roles that parasites and non-fish predators of tilapias can contribute in developing strategies for consideration in the sustainable management of the fisheries

Social Organisation of the Short-finned Pilot Whale, Globicephala macrorhynchus, with Special Reference to the Comparative Social Ecology of Delphinids

As a contribution to the understanding of comparative social trends within the cetacean family Delphinidae, a 22-month study was conducted on the shortfinned pilot whale, Globicephala macrorhynchus, which has been suggested to have a unique social system in which males and females in the same group are related and mating occurs outside of the group. The individual identification of 495 pilot whales, analysed in daily group association patterns, allowed identification of 46 pods. They were classified as productive or non-productive based on the presence or absence of immature animals. Productive pods were a significantly larger, although 12% of them lacked adult males. Two classes of whales (residents and visitors) were defined by patterns of occurrence,suggesting differential patterns of habitat use. Resident pods occasionally travelled together (41% of all groups) and associations between age and sex classes showed that in mixed-pod groups, the highest ranked associations of the reproductive females were with males from other pods, while within pods, adult males and females associated less. During summer, the proposed peak conception period, pilot whale groups were significantly larger and contained individuals from a significantly greater number of pods. These findings support the hypothesis that males and females mate when associating with individuals from other pods. A comparative analysis of sexual dimorphism, brain size, and testes size, habitat, prey and group size within the 17 delphinid genera identified a correlation between sexual dimorphism and body size, but relative measures of brain size and testes size did not correlate with broad ecological or social classifications. However, a comparison of three delphinid societies identified two distinct male mating systems: males of the small, mono-morphic Tursiops truncatus live in age/sex segregated groups and mate with a number of discrete female communities. Males in the large sexually dimorphic Glob icephala spp. and Orcinus orca mate with associated female pods and yet remain with their female kin. This corresponds to the avunculate social system described in some human societies. It could evolve from a promiscuous mating system where there is little guarantee of paternity and where males that live with their kin increase their inclusive fitness.

An assessment of water quality in integrated poultry-cum-fish reservoir, NIFFR New-Bussa in reference to maximizing the water resources potentials of Nigeria for sustainable aquaculture under the sub-theme "Fish production and the environment"

In this reservoir, the parameters being assessed are very important in the aspect of fish culture. These parameters are: physical parameters which includes temperature (O), Transparency (M).Chemical parameters include: Dissolve oxygen (mg/l) pH concentration and the Biological Parameters which include phytoplankton and zooplankton. The phytoplankton and zooplankton identification and estimation were carried out in the NIFFR Limnology Laboratory, (Green House), New Bussa. Each identified zooplankton and phytoplankton species was placed according to its major group e.g. zooplankton was grouped into three families, Roifera, Cladocera and Copepods. During this study period it was observed that copepods have the highest total number of zooplankton both beside the poultry and monk (station 'A'&'B'). Water temperature of station 'A' (beside the poultry house) ranges from 27 C-29, 5 c also same station 'B' (near the monk). Dissolve oxygen station 'A' range from 6.30mg/l-7.40mg/l while that of station 'B' ranges from 6.20mg/7.50mg/l, turbidity reading of station A'ranges from 0.19m-0.3m while station 'B' ranges from 0.22m-0.37m. The last parameter, which is pH concentration, in both stations 8.2 was observed this is an indication that the pH was constant. According to some literature review all the water parameter figures obtained were good for fish culture

A chemical survey of standing waters in south-east England, with reference to acidification and eutrophication

This study looks at the distribution and magnitude of acidification and eutrophication in south-east England where there are no natural lakes but a large number of shallow artificial ponds. The study area is defined as the region lying within a 100 km radius of central London but excluding the area within the M25 motorway. Water samples were taken from 120 sites between mid-January and the end of February 1990, with a subsequent monthly survey of a subset of 31 of these waters. Twelve chemical variables were measured in the laboratory using standard techniques. PH values for the full dataset ranged from 3.2 to 8.4, although the majority of sites had pH values in the range 7.0 to 8.5; only five sites had a pH of less than 6.0. The five low pH sites expectedly had low alkalinities and are the only sites with values below 0.1 meq per litre. Concentrations of calcium, sodium, potassium, magnesium, chloride, sulphate and nitrate had normal distributions. The majority of sites had total phosphorus concentrations in the range 25 to 200 mu g per litre, although 10 sites had concentrations above 400 mu g per litre. The low number of acid sites suggests that surface water acidity is not a widespread regional problem in south-east England. However the survey shows that a large number of standing waters in the region have high total phosphorus and nitrate concentrations, and 89% may be considered moderately to considerably eutrophic.

Some aspects of the ecology of the limnoplankton, with special reference to the phytoplankton. [Translation from: Svensk Botanisk Tidskrift 13(2) 129-163, 1919.]

This paper tries to develop more generally some fundamental bases for the ecological study of freshwater plankton. A special attention is given to the phytoplankton associations which can be separated out and made into groups according to their dependence upon changing environments. Plankton formations in different types of water bodies (ponds, lakes and rivers) are studied.

Comparative investigations on the respiratory physiology of euryhaline gammarids with special reference to salinity adaptation. [Translation from: Helgolaender Wissenschaftliche Meeresuntersuchungen 23(4) 485-534, 1972.]

Members of the family Gammaridae are very closely interrelated. There arises the question as to how far they also differ amongst themselves through physiological characteristics. Comparative respiratory and physiological experiments were made on the five euryhaline species Gammarus locusta, G. oceanicus, G. salinus, G. zaddachi and G. duebeni. The respiratory measurements carried out within the framework of this experiment were occupied with the relationships between oxygen consumption and body size depending on salinity. They also had the object of determing the variations in metabolic intensity after an abrupt change in the salt content of the external medium, and to establish the period of time for the process of adaptation. As the experiments were carried out polarographically in a testing plant with continuous flow-through, and the method which was applied permitted continuous recording over prolonged intervals, there could also be carried out comparisons between metabolism at rest and under activity, and the alterations of oxygen consumption during the process of moulting could be measured.

Reference-growth rate – a simple and handy parameter summarizing the influence of environmental conditions

Abstract Environmental changes may have an impact on life conditions of the fish, e.g. food supply for the fish. The prevailing environmental conditions apply evenly to all age groups of one stock. Small fish have high growth rates, whereas large fish grow with low rates. But, it can be shown on the basis of the von Bertalanffy-growth model that it is sufficient to know only the growth rate of one single age group to compute the growth rates of all other age groups. The growth rate of a reference fish GRF (e.g. a fish with a body mass of 1 kg) was introduced as a reference growth describing the current food condition of all age groups of the stock. As an example a time series of the reference-growth rate of the northern cod stock (NAFO, 3K) was computed for the time span 1979 to 1999. For the northern cod stock it can be observed that environmental conditions caused growth rates below the long-term mean for seven years in a row. After a prolonged hunger period the fish stock collapsed in 1992 also by the impact of fisheries - and this was probably not a coincidence. Now, with the reference-growth rate GRF a simple and handy parameter was found to summarize the influence of the environmental conditions on growth and other derived models and therefore makes it easier to compute the influence of environmental changes within stock assessment. Zusammenfassung Veränderungen der Umwelt können Auswirkungen auf die Lebensbedingungen der Fische haben, z. B. auf das Nahrungsangebot der Fische. Die vorherrschenden Umgebungsbedingungen wirken gleichmäßig auf alle Altersgruppen eines Bestandes, wobei typischer Weise kleineFische hohe Wachstumsraten haben, während die großen Fische mit niedrigen Raten wachsen. Auf der Grundlage des von Bertalanffy-Wachstumsmodells kann gezeigt werden, dass es ausreicht, nur die Wachstumsrate von einer einzigen Altersgruppe zu kennen, um die Wachstumsraten von allen anderen Altersgruppen berechnen zu können. Die Wachstumsrate eines Referenz-Fisches (z.B. eines Fisches mit einer Körpermasse von 1 kg) wurde als Referenz-Wachstum GRF eingeführt, die den aktuellen Zustand des Nahrungsangebots füralle Altersgruppen des Bestandes beschreibt. Als Beispiel wurde einer Zeitreihe der Referenz-Wachstumsraten des nördlichen Kabeljaubestandes (NAFO, 3K) für die Zeitsraum 1979 bis 1999 berechnet. Für diesen Kabeljaubestand war zu beobachten, dass Umgebungsbedingungen für sieben Jahre in Folge Wachstumsraten unter dem langjährigen Mittelwert verursachten. Nach einer längeren Hungerperiode kollabierte dieser Fischbestand im Jahr 1992 auch durch den Einfluß der Fischerei - und dies war sicher kein Zufall. Jetzt, mit der Referenz-Wachstumsrate GRF, ist ein einfacher und handlicher Parameter gefunden, der es gestattet den Einfluss der Umweltbedingungen auf die Wachstumsbedingungen und andere davon abgeleitete Modelle zusammenzufassen. Dies macht es einfach, den Einfluss von Umweltveränderungen innerhalb der Bestandsabschätzungen zu berechnen.

Invertebrate communities in northern Lake Victoria, with reference to their potential for fishery production

The zooplankton and macrobenthic communities of Lake Victoria were sampled by lift net and Ponar grab, respectively. The zooplankton comprised copepods and cladocerans, rotifers and aquatic insect larvae. Most taxa exhibited wide distribution in the lake, with the exception of rotifers which were rare in deep offshore waters. The main components in the macro-benthos were chaoborid and chironomid larvae and molluscs. Caridina nilotica (Roux) and other groups were rare in the samples. Zooplankton density ranged from 100000 or more to 4 million ind. m2 and increased from the shallow inshore to deep offshore waters. Numerical dominance of cyclopoids and nauplius larvae was a common feature at all stations sampled. Most macrobenthic taxa were also widely distributed, although chaoborid and chironomid larvae were rare in the samples. Rastrineobola argentea (Pellegrin) and larval Lates niloticus (L.) ate mainly cyclopoid copepods, while cichlids showed a strong preference for adult insects. High ecological stability of the cyclopoids, and the zooplankton community in general, despite radical ecosystem changes in recent years, coupled with what appears to be high predation pressure, offers good prospects for the pelagic fishery in the lake.

The role of Caridina nilotica (Roux) in the Lake Victoria fisheries with reference to Lates niloticus (L.)

Caridina nilotica (Roux) (Decapoda: Atyidae) was investigated over a period of four months in three zones of Lake Victoria. Abundances were estimated by vertical net sampling. The importance of C. nilotica in the diet of the three commercial fish species was investigated. Caridina nilotica is a primary food for Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin). A quantitative study of C. nilotica in the fishing area indicated high biomass which can support the Lake Victoria fisheries.

Teaching Students to Evaluate E-Reference Sources with Moodle Forums

This presentation will describe the use of online forums in Moodle, a course management system, to teach students to evaluate both print and electronic reference sources. For two semesters I have created an online forum called the Fishing Hole Scouting Report for an in-class exercise. Students are given 2-3 background questions and told to find the answers using both a library-approved reference source and Wikipedia. Students then evaluate the reference source for effectiveness and ease of use, compared to Wikipedia, and post their comments in the forum to share with the class. I will highlight the educational benefits of using Moodle forums for this purpose and discuss best practices for selecting the most effective sources and questions.

Cryogenic Silicon Optical Reference Cavities

Thermodynamical fluctuations in temperature and position exist in every physical system, and show up as a fundamental noise limit whenever we choose to measure some quantity in a laboratory environment. Thermodynamical fluctuations in the position of the atoms in the dielectric coatings on the mirrors for optical cavities at the forefront of precision metrology (e.g., LIGO, the cavities which probe atomic transitions to define the second) are a current limiting noise source for these experiments, and anything which involves locking a laser to an optical cavity. These thermodynamic noise sources scale physical geometry of experiment, material properties (such as mechanical loss in our dielectric coatings), and temperature. The temperature scaling provides a natural motivation to move to lower temperatures, with a potential huge benefit for redesigning a room temperature experiment which is limited by thermal noise for cryogenic operation.

We design, build, and characterize a pair of linear Fabry-Perot cavities to explore limitations to ultra low noise laser stabilization experiments at cryogenic temperatures. We use silicon as the primary material for the cavity and mirrors, due to a zero crossing in its linear coefficient of thermal expansion (CTE) at 123 K, and other desirable material properties. We use silica tantala coatings, which are currently the best for making high finesse low noise cavities at room temperature. The material properties of these coating materials (which set the thermal noise levels) are relatively unknown at cryogenic temperatures, which motivates us to study them at these temperatures. We were not able to measure any thermal noise source with our experiment due to excess noise. In this work we analyze the design and performance of the cavities, and recommend a design shift from mid length cavities to short cavities in order to facilitate a direct measurement of cryogenic coating noise.

In addition, we measure the cavities (frequency dependent) photo-thermal response. This can help characterize thermooptic noise in the coatings, which is poorly understood at cryogenic temperatures. We also explore the feasibility of using the cavity to do macroscopic quantum optomechanics such as ground state cooling.

Investigations on phytoplankton with special reference to water usage

Experiments and observations on the phytoplankton of certain lakes in the English Lake District were made from early 1973 to the end of March, 1974. They included laboratory and lake bioassays and observations on the quantity and quality of the phytoplankton in six lakes. The introductory sections of the report are about algae, the ecology of phytoplankton and the scope of the contracted work. Laboratory bioassays on water from one lake, Blelham Tarn, showed that phosphorus, silicon (for diatoms) and organic substances forming complexes with iron were the major substances limiting the growth of the algae tested. The growth of the test algae was limited to different degrees by those substances and, to some extent, to a greater or lesser degree at different times of year. It is suggested that a relatively simple form of bioassay could give valuable information to water undertakings. Lake bioassays and other experiments were carried out by using large in situ tubular plastic enclosures. Two such investigations are described. The effects of a change in sewerage in two drainage basins on the phytoplankton of three lakes is described and some data given about changes since 1945 in three other lakes in the same overall drainage basin. These latter lakes have been affected too by changes in sewerage and by increasing inputs of domestic and agricultural wastes. Throughout, the relevance of the work done to practical problems of water usage is kept in mind and discussed. In the last section special reference is made to the largely unpredictable results of water transfers. The report ends with a note on river phytoplankton.

Management of Biesboch reservoirs for quality control with special reference to eutrophication

The three Biesbosch Reservoirs are pumped storage reservoirs, fed with rather polluted and highly eutrophic water from the River Meuse. Air injection at the bottom of the reservoirs prevents thermal stratification, which would otherwise result in serious water quality deterioration. Reservoir mixing also serves as an economic algal control measure; mixing over sufficient depth causes light to play the role of limiting factor and this, combined with zooplankton grazing, keeps the biomass of phytoplankton at acceptable levels. Special problems are caused by benthic, geosmin-producing Oscillatoria species growing on the inner embankment. Rooting up the bottom with a harrow is used as the method of control, based on underwater observations by biological staff trained as SCUBA-divers. With regard to pollutant behaviour the three reservoirs act as a series of fully mixed reactors. This enables the application of kinetic models to describe their behaviour and allows the use of a selective intake policy, e.g. for suspended solids with associated contaminants, ammonia and polynuclear aromatic hydrocarbons. A combination of selective intake and self- purification processes - enhanced by the compartmentalisation of the storage volume in three reservoirs - leads to a striking improvement for many water-quality parameters.

On statistical treatment of the results of parallel trails with special reference to fishery research

Parallel trials form a most important part of the technique of scientific experimentation. Such trials may be divided into two; categories. In the first the results are comparable measurements of one kind or another. In the second the data consist of records of the number of times a certain 'event' has occurred in the two sets of trials compared. Only trials of the second category are dealt with here. In this paper all the reliable methods of testing for significance the results of parallel trials of a certain type with special reference to fishery research are described fully. Some sections relate to exact, others to approximate tests. The only advantage in the use of the latter lies in the fact that they are often the more expeditious. Apart from this it is always preferable to use exact methods.