摘要:

AbstractA simple siphon raises water over a crest and discharges it at a lower level. As water flows through a siphon, energy due to pressure and elevation is either lost to pipe friction or converted to velocity energy. For most practical siphons, between 50 and 75% of the elevation energy available to drive flow will be converted to velocity energy.A standpipe covered with a dome will begin to siphon when the standpipe flows full. During siphoning, the flow rate may be several times higher than the flow through an uncovered standpipe of the same size. Furthermore, the covered standpipe can be designed to lower the water level to a point below the top of the standpipe before siphoning is allowed to stop.Flow into the covered standpipe can be drawn from the bottom of the reservoir by extending the skirt of the dome. A vent tube allows easy adjustment of the elevation at which air enters the dome and siphoning stops. Flow rate and water level required to start the siphon depend on the pipe diameter. Some flow through the standpipe will occur before siphoning begins. Flow into the reservoir must be greater than the flow required to start siphoning. Maximum flow through the standpipe during siphoning depends on pipe diameter and the elevation energy driving the flow.Adding a trap to the outlet of the covered standpipe eliminates the leakage flow prior to the start of siphoning. When air bubbles out the trap at the end of the standpipe, pressure inside the dome is released suddenly allowing the water level to jump above the critical level needed to start siphoning. For reliable operation, the crest height of the trap should be about equal to one diameter of the standpipe. The vent tube opening must be below the top of the standpipe to prevent premature overflow of the standpipe. Because a trapped outlet siphon has no minimum flow limit, the standpipe can be sized to carry any maximum flow.While the trapped outlet siphon eliminates low rate leakage flow prior to the onset of siphoning, the height differential between the start and stop of siphoning cannot be as small or as easily adjusted as with a covered standpipe without a trap. The simple siphon is convenient for some applications, but it does not lend itself to automatic cycling operation. The choice depends on the needs of the situation.

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00710.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractInadequate information pertaining to the growth potential of the US. processed catfish industry has been a major factor leading to cyclical periods of excess supply or demand resulting in misal‐location of resources and price instability. Better information for industry planners (e.g., producers, processors, government regulatory agencies, and university researchers) on future sales potential would assist in decreasing the misuse of resources. An econometric model of wholesale demand for US. processed catfish was developed to provide estimates of future sales under various scenarios. In addition to the standard variables included in models of demand for food items—price, income, and population—the effects of product life cycle and industry‐sponsored generic advertising are quantitatively incorporated. Seasonality of demand and rigidities in marketing and consumer behavior are additional considerations explicitly modeled via monthly dummy variables and a Ner‐lovian partial adjustment mechanism, respectively.Model results indicate the impact of alternative future price scenarios on wholesale processed caffish sales. At the mean real wholesale price of $1.60 (December 1988 dollars) for whole‐dressed caffish and a real generic advertising expenditure of one million dollars postulated for 1995, projected aggregate sales are 219.2 million pounds, a 23% increase over 1989 sales. Projected 1995 wholesale sales are very sensitive to price with alternative price postulations of $1.40 and $1.80 resulting in projected sales of 252.3 and 193.6 million processed pounds, respectively. An estimated 7% average increase in wholesale sales of catfish was attributed to the industry‐sponsored generic advertising campaign. Model projection estimates and impacts are posed as a quantitative source of information to be used with other information in resource allocation issues faced by industry de

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00711.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of four levels of diffused aeration (0, 6, 12, and 24 hours/day) and two stocking densities (400 and 600 fish/m3) on the culture performance of caged Florida red tilapia were evaluated in 1 m3cages in a 2 ha watershed pond on St. Croix, U.S. Virgin Islands. Fish obtained a nutritionally‐complete (36% protein), floating feed from demand feeders for 143 to 146 days. Diffused aeration had no significant (P>0.05) effect on fish growth, survival, feed conversion, and production in cages. Combined across all levels of diffused aeration, fish stocked at 400/cage had a greater growth rate (2.21 vs. 1.97 g/day), larger final body weight (370 vs. 335 g), and a lower feed conversion ratio (1.69 vs. 1.80) than fish stocked at 600/cage (P<0.05). The final biomass of fish stocked at the higher density (181 kg/m3) was greater than at the lower density (140 kg/m3). The enhancement of water exchange rates by diffused aeration did not increase tilapia growth rate or production in cage

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00712.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBlood samples were collected from captive Pacific halibut,Hippoglossus stenolepis, at intervals of about six weeks from early December 1986 to late November 1987. Concentrations of plasma androgen and estradiol‐17β were determined by radioimmunoassay. The plasma concentrations of steroid were highest during autumn and winter in halibut that matured during late winter. The concentrations of steroids in samples collected in December were above 2 ng/mL (estradiol) or 1 ng/mL (androgen) in maturing females and below 0.5 ng/mL for both steroids in non‐maturing females. The levels of steroids decreased rapidly about one month before spawning. In a mature male, androgen began to rise in August and November, and reached a peak of 7 ng/mL in early December. One month before spawning, the androgen concentration fell to 0.16 ng/mL. Estradiol concentrations were detectable in the male and varied little during the year. In immature fish, neither androgen nor estradiol changed significantly throughout the year. These results suggest that the concentrations of estradiol or androgen measured in blood samples taken during December may be used to determine the sex and state of maturation of Pacific hal

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00713.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractCommercial‐scale production of Florida red tilapia (Oreochromissp.) seed (eggs, sacfry, and fry) under methods that minimized freshwater usage was studied on Lee Stocking Island, Bahamas. Comparisons of seed production by broodstock held in low‐salinity (LS = 5 ppt; mixed rain and ground water) and brackish‐salinity (BS = 18 ppt; mixed ground and sea water) tanks (34 m2) showed that seed production over an 8 month period was significantly greater in LS (77.7 seed/m2/ day) than in BS tanks (47.4 seed/m2/day), with average proportion of brooding females and number of seed per clutch being greater in LS (26.9% and 763) than in BS tanks (19.8% and 643). While LS seed production was among the highest reported values for tilapias, BS production was within reported ranges for fresh and low‐salinity tilapia hatcheries. Seed production per unit of low‐salinity water (i.e., rain and/or groundwater) consumed in both LS (7,262 seed/m3) and BS (5,337 seed/ m3) tanks exceeded reported values. The results support the feasibility of commercial‐scale production of Florida red tilapia seed under intensive methods and of salinities as high as 18 ppt in regions where fresh or low‐salinity water resource

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00714.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractMaturation and spawning of blue shrimpPenaeus stylirostriswere obtained in hypersaline and turbid water. Results indicate that number of spawnings per female and percentage of viable spawnings are similar to those reported under “standard” conditions by other investigators. However, the number of nauplii produced was 50 to 75% less. A significant correlation was observed between reproductive activity and lunar cycles, showing peak activity at three to four days following new moon. Additionally, working with records of individual females, the number of spawnings per female was found to be extremely variable, with intervals between consecutive spawnings non‐uniform. Instead, they tended to group in pairs with less than six days between spawnings, followed by a variable period of time (usually more than 12 days) before the paired spawnings were rep

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00715.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractMetupenaeus ensislarvae at different stages were exposed to a series of nitrite‐N (nitrite as nitrogen) concentrations in static renewal toxicity tests. Larvae at zoea stage were the most susceptible, and postlarvae were the most tolerant to nitrite among the larvae tested. The 24 h LC50s were 31.29, 16.05, 47.60 and 70.06 mg/L nitrite‐N for third nauplius substage (N3). second zoea substage (Z2), second mysis stage (M2), and first postlarva substage (PL1), respectively, in 33 ppt seawater at a pH of 8.20 and a water temperature of 30 C. The 48 h LC50for M2 and PL1 were 20.67 and 27.10 mg/L nitrite‐N, respectively. The “threshold time” was 108 h, and the “incipient LC50” forM. ensisPL1 was 7.06 mg/L nitrite‐N. A “safe level” for rearingM. ensislarvae was estimated to be 0.71 mg/L nitrit

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00716.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractNitrogen ingested by the rotifer,Brachionus plicatilis(S type) is balanced by gain in body nitrogen (including reproduction), soluble excreted nitrogen, and nitrogen as egested feces. Every term in the budget was estimated independently, and measured as directly as possible. A comparison of the observed and calculated nitrogen as egested feces yielded a satisfactory result.The nitrogen ingested by the rotifer was distributed as follows: 15.6% for growth and reproduction, 42.0% for metabolic excretion, and 42.4% as feces. From these results, it was concluded that a large proportion (84%) of the nitrogen ingested by the rotifer is transferred to water in various forms and may cause deterioration of the water quality.

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00717.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPond water quality and associated microbial biomass were studied in relation to the type of feed applied during the culture of the marine shrimpPenaeus vannamei. The feeds tested included conventional feedlot manure as well as two feeds based on bagasse, a sugarcane waste product. Physical and chemical parameters were studied during a 100 day trial in 200 m2earthen ponds. Both bagasse‐based feeds supported a significantly larger microbial community as measured by specific biomass numbers (P<0.01), ATP content (P<0.001) and amount of the particulate organic matter present on pond bottoms (P<0.025). For both bagasse‐based treatments, the estimated bacterial cell number in the flocculent layer was 3.11 ± 1012/m2, compared to the much lower cell number of 7.53 ± 1010/m2for control ponds. Harvest data suggest that bagasse forms a potential base for feeds when applied to extensive shrimp cul

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1991.tb00718.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY