Effects of dietary carbohydrate and fibre on the tilapia Oreochromis niloticus (Linn.)

Glucose, sucrose, dextrin, starch and a-cellulose were incorporated into experimental rations at three levels (10%, 25% and 40%) and fed to juvenile O. niloticus for 63 days. Inclusion level was adjusted with polypropylene powder. Growth improved as the level of glucose, sucrose, dextrin and starch was increased from 0% to 40%. Carcass fat similarly increased with the addition of assimilable carbohydrate (maximum level 8.2% liveweight). At the 40% level, net protein retention (NPR) was highest on the dextrin diet and lowest on the glucose diet. At 10%, glucose spared more, and at 40%, spared less protein energy in the diet than dextrin, starch or sucrose at corresponding levels. The value of these carbohydrates for replacing protein energy in rations for tilapia is discussed.As a-cellulose was increased from 0% to 40%, growth, food conversion efficiency (FCE), NPR, carcass fat and condition factor were reduced. Growth and FCE on the 25% and 40% a-cellulose diets was lower than the control. The use of a-cellulose as an inert bulker in experimental diets for fish is discussed.     

Intake and discharge nutrient loads at three intensive shrimp farms

This study was conducted to help provide a framework for Australian regulation of shrimp farm siting and discharges. Monitoring of farm water usage, and intake and discharge water quality was conducted at three commercial intensive shrimp farms, chosen to represent different operating environments, latitudes, cultured species and management styles. Weekly samples were taken over 3 years, for 3–12 months at each farm, to investigate intake and discharge concentrations and loads of total suspended solids (TSS), total nitrogen (TN) and total phosphorus (TP). Mean water exchange was 1.4 ML ha^?1 day^?1 (about 10% day^?1) at the first farm studied and 0.5 ML ha^?1 day^?1 (about 3.6% day^?1) at the others. Farm mean discharge concentration varied as follows: TSS, from 36.9 to 119 mg L^?1; TN, from 2.1 to 3.1 mg L^?1 and TP, from 0.22 to 0.28 mg L^?1. Farm mean intake concentrations were from 11% to 91% of equivalent mean discharge concentration (for TN at Farm B and TSS at Farm C respectively). Mean net discharge loads, related to area of production ponds at each farm, varied as follows: TSS, from 4.8 to 85.7 kg ha^?1 day^?1; TN, from 1 to 1.8 kg ha^?1 day^?1 and TP, from 0.11 to 0.22 kg ha^?1 day^?1. The highest net loads of TSS, TN and TP were all from the farm with the highest water exchange rate, located on a coastal river, and studied during a year of high rainfall with associated poor water quality. These results can be used to help predict likely discharge characteristics for new shrimp farms, and provide a benchmark against which to evaluate future improvements in shrimp farm environmental management.     

Characterization of intake and effluent waters from intensive and semi-intensive shrimp farms in Texas

Two commercial shrimp farms in south Texas were evaluated for influent and effluent water quality from June to October 1994. The intensive farm, Taiwan Shrimp Village Association (TSV) had an average annual yield of 4630 kg ha^?1 while the semi‐intensive farm, Harlingen Shrimp Farm (HSF), had a yield of 1777 kg ha^?1. The study had three objectives: (1) to compare influent and effluent water from the intensive and semi‐intensive shrimp farms, (2) to show which effluent water‐quality indicators exceeded allowable limits, (3) to indicate inherent problems in farms operated with water exchange and summarize how findings from this study led to changes in farms' management that limited potential negative impact on receiving streams. Water samples were collected and analysed twice a week for the TSV farm and once a week for the HSF farm. Samples were analysed for dissolved oxygen (DO), salinity, pH, ammonia‐nitrogen (NH₃‐N), nitrite‐nitrogen (NO₂‐N), nitrate‐nitrogen (NO₃‐N), total phosphorus (TP), total reactive phosphorus (TRP), five‐day carbonaceous biochemical oxygen demand (cBOD₅), total suspended solids (TSS) and settleable solids (SettSols). Most of the effluent constituents showed fluctuations throughout the sampling period often related to harvest activity. Effluent pH at TSV was lower than influent values but within the regulatory requirements set by Texas Commission of Environmental Quality (TCEQ), formerly known as Texas Natural Resource Conservation Commission (TNRCC). HSF effluent pH values were higher than its influent, but still within TCEQ limits. Effluent DO mean levels were generally below the regulatory daily mean requirement, with values at TSV often below those for influent. Effluent nutrient concentrations and net loads were generally higher at the intensive shrimp farm, with NH₃‐N mean concentrations above the daily mean set by the TCEQ on several occasions. Effluent TSS concentrations were higher than influent for both farms, with daily mean values above the TCEQ limit. The two farms presented similar TSS concentrations despite their different stocking densities. However, TSS total net load and net load per hectare were higher at the intensive farm. The semi‐intensive farm presented higher cBOD₅ concentrations and net loads despite its lower stocking density, with daily mean values above the TCEQ limit. The cBOD₅ net load at TSV presented negative values indicating higher load at the influent than at the effluent. Analyses showed no evidence of self‐pollution between influent and effluent at the two farms. The high feed conversion ratio (FCR) values (2.3 and 2.7 for the intensive and the semi‐intensive farm respectively) suggest that better feed management is needed to reduce nutrient and solid net loads release from the two farms. The data obtained from this study resulted in several modifications in design and management of the two farms that reduced the potential negative impact on receiving streams. A brief summary of the improvement in selected effluent water‐quality indicators at the intensive shrimp farm is provided.     

Connectivity,habitat, and flow regime influence fish assemblage structure: Implications for environmental water management in a perennial river of the wet–dry tropics of northern Australia

1. Environmental water management seeks to balance competing demands between the water needed to sustain human populations and their economic activities and that required to sustain functioning freshwater ecosystems and the species they support. It must be predicated on an understanding of the environmental, hydrological, and biological factors that determine the distribution and abundance of aquatic species.
2. The Daly River of the wet–dry tropics of northern Australia consists of a perennially flowing main stem and large tributaries, as well as many small to large naturally intermittent tributaries, and associated off‐channel wetlands. Increased groundwater abstraction to support irrigated agriculture during the dry season threatens to reduce dry‐season flows that maintain perenniality and persistence of freshwater fishes.
3. Fish assemblages were surveyed at 55 locations during the dry season over a 2‐year period with the goal of establishing the key landscape‐scale and local‐scale (i.e. habitat) drivers of fish species distribution.
4. Longitudinal (upstream/downstream) and lateral (river/floodplain) gradients in assemblage structure were observed with the latter dependent on the position in the river landscape. Underlying these gradients, stream flow intermittency influenced assemblage composition, species richness, and body size distributions. Natural constraints to dispersal were identified and their influence on assemblage structure was also dependent on position within the catchment.
5. Eight distinct assemblage types were identified, defined by differences in the abundance of species within five groups differing in functional traits describing body size, spawning requirements, and dispersal capacity. These functional groups largely comprised species widely distributed in northern Australia.
6. The results of the study are discussed with reference to the environmental flow needs of the Daly River and other rivers of northern Australia. The findings may also be applied to environmental flow management in savannah rivers elsewhere.

     

Use of endoscopy for gender and ovarian stage determinations in Russian sturgeon (Acipenser gueldenstaedtii) grown in aquaculture

The Russian sturgeon (Acipenser gueldenstaedtii) is native to the Caspian Sea, the Black Sea and the Azov Sea. It used to breed in the main incoming rivers, until dam construction in the mid 20th century blocked upriver spawning migration. Aquaculture of Russian sturgeon has only recently begun, prompted by their declining populations in natural habitats and the rise in meat and caviar prices. However, information on their gonadal development and puberty under culture conditions is incomplete.

Because sturgeons have no external sexual dimorphism and there are no external markers for sexing, internal examination of the gonads must be employed for gender identification as well as to monitor their development. The present study describes endoscopic and histological observations of the gonads of young Russian sturgeons aimed at identifying gender and monitoring ovarian developmental stage in females up to the age of 6 years, when they enter their first puberty cycle, as well as at 7 years of age, when they have completed vitellogenesis, under culture conditions. This information, as related to fish age and size, is of vital importance to commercial farming of Russian sturgeon for caviar production and reproduction.

For gonadal observations in both sexes, we used an endoscopic system consisting of a 4 mm, 14 cm long cystoscope sheath incorporated with fiber-optic light transmission, connected to a halogen cold light source and a miniature videocamera with a control unit attached to a color monitor. This system allowed us viewing of the fish's abdominal organs, and to save pictures of selected areas of the gonads on a computer as the fish's personal record. Ovarian biopsies were taken in parallel for histology at typical stages of gonadal development.

Gender could be identified with this system as early as at 3 years of age and the sex ratio under culture conditions of females, males and unidentified gender were 55, 40 and 5%, respectively.

Not only did large differences occur in the developmental stages of female of the same age group, but also ovarian development was highly asynchronous at the early vitellogenic stages. In late vitellogenesis, at the “gray egg” stage (1600–2600 μm diameter), the oocytes were quite regular in size and color, and remained so until the final stages of maturity.

Our study suggests that endoscopy is an efficient method for both gender identification at an early age, and for determination of gonadal development stage in sturgeon aquaculture. The ability to see the whole intact gonads of anesthetized fish can reveal important management and research information, with minimal damage or stress to the fish.     

Role of sulfur and chloride in the dietary cation-anion balance equation for lactating dairy cattle

Ten Holstein cows averaging 120 d in lactation were arranged in replicated 5 x 5 Latin squares with 3-wk periods to evaluate the role of sulfur (S) in the dietary cation-anion balance equation. Diets were based on corn silage in Exp. 1 and sorghum silage in Exp. 2. Supplemental S and chloride (Cl) from the double sulfate of potassium and magnesium and CaCl2 were used to manipulate dietary cation-anion balance from 0 to +30 meq when expressed as meq [(Na + K)-(Cl + S)]/100 g diet DM and from +19 to +49 meq when expressed as meq [(Na + K)-Cl]/100 g diet DM. Blood pH was not affected by cation-anion balance, although both S and Cl supplementation tended to lower pH. Blood HCO3- and urine pH decreased and plasma calcium (Ca) and urinary Ca excretion increased as anion was added to the diet. Milk fat production tended to be increased by the low S supplementation. Dietary Cl and S had similar effects on acid-base status. Therefore, we suggest that S be included with Cl in the dietary cation-anion balance equation for lactating dairy cows as follows: meq [(Na + K)-(Cl + S)]/100 g diet DM. Although response of acid-base status to S and Cl was similar, as more data comparing the acidogenicity of S vs Cl become available, it may be necessary to include a modifying coefficient for S in the equation to adjust for differences between S and Cl in acid-generating potential. This coefficient may be further dependent on the dietary source of S.     

Chlamydiosis in workers at a duck farm and processing plant

SUMMARY An outbreak of chlamydiosis was Investigated in workers at a duck farm and processing plant during winter 1989. Chlamydia psittaci was isolated from ducks, but there was little evidence of clinical chlamydiosis in the ducks. Serological tests showed that 76% of workers had been exposed to Infection, 12% recently, 16% had not been exposed and 8% had inconclusive test results. There was a strong association (P < 0.05) between years of employment and exposure to Infection. Infection appeared to be contracted during the first year of employment. Measures were Implemented to reduce shed contamination and control rodents and wild birds. At the same time, ducks were medicated, the processing plant was modified, work practices were altered and workers were advised about chlamydiosis to reduce the risk of human infection.