Browsing by Subject "Tilapia"

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Effects of low dietary levels of saponins on two common culture fish - common carp (Cyprinus carpio L.) and Nile tilapia (Oreochromis niloticus (L.))
(2001) Francis, George; Becker, Klaus
Saponins are a group of compounds present in many wild plants and cultivated crops and are commonly found in traditional medicinal preparations. Feeding experiments using saponin-supplemented (commercial Quillaja saponin) feeds were conducted in two commonly cultured fish species, namely common carp (Cyprinus carpio L.) and tilapia (Oreochromis niloticus (L.)). Quillaja saponins (QS) at dietary levels of 150 mg kg-1 and 300 mg kg-1 significantly increased body weight gain in common carp and Nile tilapia compared to controls. When fed to tilapia fry QS (700 mg kg-1) altered the normal 1:1 sex ratio. In separate, in vitro measurements it was found that QS stimulated the release of leutinising hormone (LH) from cultured tilapia pituitary cells, but apparently this did not happen in vivo since serum levels of LH were not found to be elevated in the saponin fed fish. Dietary saponins were also found to affect serum and muscle cholesterol levels. Adult tilapia - but not tilapia fry - fed a dietary level of 300 mg kg-1 QS were found to have significantly higher muscle cholesterol levels than fish fed the control diet. In tilapia fry, the average serum cholesterol levels in males showed a steady increase from dietary QS levels of 0 to 700 mg kg-1, while no such trend existed among the females. Supplementation with 50 and 100 mg kg-1 of Yucca schidigera butanol extract (containing steroidal saponins) did not significantly promote the growth of carp despite showing initial promise. The purified haemolytic fraction of triterpenoid Gypsophila saponin extract (isolated using column chromatography) did not produce any toxic effects in carp at dietary levels up to 250 mg kg-1 in a preliminary feeding trial. A growth promoting effect was however evident at the very low level of about 5 mg kg-1 when the purified fraction was used. More research needs to be done to determine the mechanisms of action of QS and to test whether saponins from other sources have similar effects.
Seasonal variation in growth, quantitative and qualitative food consumption of milkfish, Chanos chanos (Forsskål 1775), and Nile tilapia, Oreochromis niloticus (L. 1758), in Laguna de Bay, Philippines
(2002) Richter, Hartmut; Becker, Klaus
Laguna de Bay, the largest lake in the Philippines, lies directly southeast of the capital Manila. The lake has a mean depth of only 2.8m and a muddy bottom which is stirred during windy weather, causing turbid conditions (Secchi depth <30cm). In the dry season, the water level drops below that of the nearby sea, leading to a backflow of saline water which clears the water until the return of the monsoon winds (Secchi depth >100cm) and leads to algal blooms. Since the beginning of the 1970s, the lake has been used for culturing milkfish, Chanos chanos (Forsskål), in large netpens (max. 2000ha) and Nile tilapia, Oreochromis niloticus (L.), in smaller cages (max. 200m2). Initially, it was possible during the algal blooms to grow fish from fingerling (ca. 10g) to marketable size (ca. 200g) in three months, making two harvests a year possible. Aquaculture quickly spread until in the middle of the eighties, over a third of the lake was covered with cages. At the same time the growth of the fish declined, which was attributed to the excessive use of primary production. Since then, despite a reduction in aquaculture coverage to the generally recommended level of 10% of the lake, fish growth has never reached the levels of the early days of culture. In the present work, seasonal variation in growth, feeding spectrum and daily ration of these two species was to be investigated in relation to water quality in order to find out more about the interaction between aquaculture and the lake. Between May 1995 and August 1997, milkfish and tilapia were sampled on several occasions at commercial operations over the 24-hour cycle. Since milkfish, unlike tilapia, do not receive supplemental feed, the proportion of their growth derived only from natural food could be determined from the cultured fish. Tilapia were kept in cages without feed specially for this purpose and measured and weighed twice a month between March and November 1997. At the same time, selective water quality parameters (particulate organic and inorganic matter, Chlorophyll-a, zooplankton) were analysed weekly. The growth of unfed fish was significantly faster between saltwater intrusion (mid-May) and the return of the monsoons (late July) than at other times of the year. On the other hand, food consumption was only slightly higher in tilapia when the water was clear than at other times and in milkfish hardly differed over the year. Both species mainly fed on amorphous organic detritus; significant levels of phytoplankton were only found in the stomachs at times of algal bloom. In supplemented tilapia, the daily ration still consisted of 35-75% natural food, suggesting that pelleted feed was used inefficiently. The main factor limiting fish growth therefore seemed to be food quality since detritus has often been shown to be poor quality food. The weekly water samples collected in 1997 demonstrated that the total level of phytoplankton was not necessarily higher at times of rapid fish growth. The main difference was related to algal size, since at times of turbid water, small diatoms dominated but these were replaced by larger blue-green algae after saltwater intrusion. In conjunction with the feeding method of these fish, the strongly seasonal growth of the fish could now be explained. Phytoplanktivorous fish such as milkfish and tilapia can only select their food on the basis of size. Since the organic detritus in the lake consisted of particles smaller than 15µm, it was possible for the fish to selectively filter larger blue-green algae but not smaller diatoms. This could also explain why fish growth rates did not recover after a reduction in aquaculture in the mid-eighties, since the relationship between the level of algae and that of detritus seems to be more important than total algal biomass. In order to increase production to those levels found in the early seventies, the level of detritus in the lake would have to be reduced, for which its origin would have to be investigated first.
Zur Lokalisation und Funktion des Calciumtransporters im Innenohr von Knochenfischen (Oreochromis mossambicus)
(2014) Knie, Miriam; Hilbig, Reinhard
In fish the perception of gravity takes place in the otolithic organs of the inner ear. These structures are filled with endolymph fluid and posses a sensory macula epithelium on which the otolith, the so called inner ear stone, is attached. The otoliths mainly consist of calcium carbonate which is embedded in a protein matrix. The otolith growth is subjected to a diurnal rhythm. Up to now, it is not clear how the calcium ions, which are needed for the otolith minerlisation, are transported through the sensory epithelium into the endolymph. The aim of this study was to analyze the localization and function of the plasmamembrane-calcium ATPase (PMCA) as a candidate for the calcium transporting protein in the inner ear sensory epithelia of Oreochromis mossambicus with regard to the otolith biomineralization. This study was carried out using larval cichlids in different developmental stages, because in the course of the larval development, the otoliths are characterised by a rapid increase in size and dynamic rearrangements. In addition, further mineralised tissues like the teeth and the skull bones have been analysed. Moreover, the organs generally participating in the calcium metabolism like gills, intestine and kidney have been examined in the same developmental profiles. All analysed epithelia and tissues are charaterised by a co-expression of the PMCA-isoforms 1 to 4 throughout the larval development. Based on the results of this study it can be assumed that each of the four PMCA-isoforms fullfills a specialised function in the examined epithelia and tissues. In the inner ear sensory epitehlia PMCA 1 is involved in the transport of calcium ions into the endolymph, whereas isoform 2 rather performs the function of a "housekeeping gene" and is important for the maintenance of the basal calcium concentration. In the bones, the calcium export function is mainly performed by the isoforms 1 and 4, the basal calcium levels are kept stable by isoform 3. Thus the regulation of the calcium ions may be a complex and delicately regulated process. The results of the expression analysis - a specific reaction with the sense-, as well as the antisense-probe - led to the assumption that, in addition to the sense-RNA, also naturally occuring antisense-RNA is transcribed for the four plasmamembrane-calcium ATPase isoforms in Oreochromis mossambicus. These hypothesis was tested with the Northern Blot method, thereby further clues for the existence of natural antisense-RNA have been obtained. Naturally occuring antisense-transcripts can either directly serve as a template for transcription or influence the expression of the corresponding sense-RNA. To check if this is also true for Oreochromis mossambicus quantitative in-situ hybridizations in the context of the diurnal otolith growth rhythm have been performed. By the help of this method it was possible to observe changes in the expression levels of both transcripts, as well as changes in the ratio between sense- and antisense-RNA. Herefrom it was deducible, that the regulation of PMCA in the inner ear sensory epithelia may occur via the transcription rate, as well as by the expression of the antisense-transcripts themselves, in this case probably the ratio between the sense- and antisense-RNA matters. Which of the regulatory mechanisms known for naturally occuring antisense-RNA is acting in detail requires further research.