Use of simple fat analysis for evaluating quality changes in intermediate moisture fish stored at tropical temperature

Changes in the quality of intermediate moisture (IM) fish during storage at 38°C were monitored by assessing the moisture content, pH, acid value, peroxide value and thiobarbituric acid (TBA) value periodically. Results adequately portrayed the hydrolysis and peroxidation of fats and the concomitant protein degradation and crosslinking reactions that have been shown by more sophisticated methods to occur in intermediate moisture fish. Since these changes markedly affect the organoleptic quality, acceptability/shelf-life and nutritive value of IM flesh-foods their predictability by simple fat analytical techniques is of practical value where/when the more sophisticated monitoring techniques are not feasible.

Trophic State Index, morphoedaphic index and fish yield prediction in a sub-tropical lake, Manchar (Sindh), Pakistan

Limnological factors of a sub-tropical lake Manchar were studied on seasonal basis. The mean values of various parameters were: transparency, (secchi disc reading): 90.5 cm, Orthophosphate: 0.257 mg/l, TDS: 3310,5 mg/l, Conductivity: 5232 µs/l, Total Chlorophyll (Planktonic): 31.3 µg/l Planktonic biomass: 5466 µg/l. Trophic state index (TSI) was calculated by using Carlson's (1977) equations. Mean TSI for transparency was 61, while for orthophosphate and chlorophyll, it was 82 and 64 respectively. TSI values indicate advanced eutrophic state of Manchar Lake. Morphoedaphic index (MEI) was also calculated on seasonal basis. The mean values were, TDS: 1103, conductivity: 1744, alkalinity: 60, transparency: 29 and biomass (plankton dry weight): 1746. Fish yield prediction for Manchar Lake (Z =3m, mean area=100 km²) was calculated by using MEI values. The results were quite different among various parameters. Conductivity (89.1mt/y), biomass (67.6 mt/y) and TDS (44.6 mt/y) were found to be good predictors of fish yield. Chlorophyll, transparency and alkalinity values gave very low estimate.

The genetic garden

The article discusses some strategies in the establishment of a mangrove genetic garden where species could be maintained. The genetic garden is a sustainable way to prevent further damage of the remaining mangroves. Its prime function is the protection and conservation of mangroves for sustainable use.

The toxicity of four insecticides and a herbicide under tropical conditions

The toxicities of four insecticides and a herbicide to Tilapia macrochir were tested in the laboratory. The 24 hour LC50's were estimated as follows: Endrin 20% ,0.008 ppm; Lindane 5% granules, 4.6 ppmm; Synexa 50 (HCH) 50%), 5.6 ppm; Synex 25 (HCH 25%), 14.8 ppm; TOK herbicide (Nitrofen), 100% survival for 24 hours at 100 ppm. These estimates agree with results obtained by other workers elsewhere in the world. The laboratory determination of toxicity is important in estimating the direct effects of poisonous substances on fish, but other indirect effects may result from their use. These should be investigated in the field.

The significance of the pycnocline in tropical lakes

The vertical temperature profile is a poor indicator of sratification in most tropical lake. Data from Lake Bunyonyi, Uganda, showed, however, that the density profile highlighted discontinuity layers whieh were not obvious from the temperature profile, It is suggested that the vertical density profile and the region of maximum discontinuity, the pycnocline, could be adopted as a useful index of stratification especially in tropical lakes.

Helminth fauna of Oreochromis leucostictus (Pisces: Cichlidae) from a tropical lake, Lake Naivasha, Kenya

The helminth fauna of Oreochromis leucosticus (Trewavas) from Lake Naivasha is described. The study was carried out on 1,050 gillnetted fish caught over a period of 24 months at different sites within the lake. Oreochromis leucosticus which is a commercially important fish was observed to be a host of four helminth parasites. These were an acanthocephalan polyacanthorhynchus kenyensis (Schmidt and Canaris), a nematode contracaecum sp.. a trematode clinostomum sp. and a dilepidid cestode Amirthalingamia sp. Seasonal variation in prevalence, intensity of infection, organs infected and the variation in infection with the size, sex and body condition of the host are described. There was no seasonal variation in prevalence but intensity of infection was observed to increase with the age of the fish. Although male fish were observed to be more heavily infected, the parasites did not seem to have any significant effect on the body condition of the fish.

SPECIES DIVERSITY DYNAMICS OF FRAGMENTED TROPICAL RAINFORESTS IN THE LOWER-LANCANG/ UPPER-MEKONG RIVER BASIN

　在澜沧江下游/ 湄公河上游的滇南西双版纳地区,通过样方法比较了热带雨林的连片与3 个小片断的物 种多样性变化趋势。与连续森林比较,片断热带雨林的植物物种丰富度和物种多样性指数都比较低,而且有相当低 比例的大高位芽、中高位芽和附生等生活型植物,而藤本、小高位芽和矮高位芽等生活型植物的比例则较高;泛热 带、热带亚洲至热带非洲的区系成分比例较高,而当地成分则减少;群落的上层树木比下层树木更加稳定。同样,动 物的物种多样性指数和均衡度在片断热带雨林中都较低,与其密切相关的是片断热带雨林的环境质量,而不是片 断的大小。此外,也探讨了片断热带雨林物种变化与森林小气候的关系,阐明了由凉湿向干暖转化的“林内效应"是 其物种变化的重要原因之一。

Vertical mixing within the epilimnion modulates UVR-induced photoinhibition in tropical freshwater phytoplankton from southern China

1. The importance of vertical mixing in modulating the impact of UVR on phytoplankton photosynthesis was assessed in a tropical, shallow lake in southern China from late winter to mid-spring of 2005. 2. Daily cycles of fluorescence measurements (i.e. photosynthetic quantum yield, Y) were performed on both 'static' and in situ samples. Static samples were of surface water incubated at the surface of the lake under three radiation treatments - PAB (PAR + UVR, 280-700 nm), PA (PAR + UV-A, 320-700 nm) and P (PAR, 400-700 nm). In situ samples were collected every hour at three different depths - 0, 0.5 and 1 m. 3. The general daily pattern was of a significant decrease in Y from early morning towards noon, with partial recovery in the afternoon. Samples incubated under static conditions always had lower Y than those under in situ conditions at the same time of the day. 4. Under stratified conditions, no overall impact of UVR impact could be detected in situ when compared with the static samples. Further rapid vertical mixing not only counteracted the impact of UVR but also stimulated photosynthetic efficiency. 5. Based on these measurements of fluorescence, the mixing speed of cells moving within the epilimnion was estimated to range between 0.53 and 6.5 cm min(-1). 6. These data show that mixing is very important in modulating the photosynthetic response of phytoplankton exposed to natural radiation and, hence, strongly conditions the overall impact of UVR on aquatic ecosystems.