摘要:

AbstractWater recirculating systems are becoming more prevalent as wild fish supplies and fresh water sources become increasingly scarce. As water recirculating rates increase, the accumulation of fine and dissolved solids can degrade water quality and fish productivity. Foam fractionators have been used with some success to remove these solids, although an understanding of how to best operate such units is currently lacking. The foam enrichment process occurs as bubbles travel from the bottom of a fractionator column to the top of the water column. Factors affecting bubble enrichment include several operating or design parameters under operator control or influence, e.g, water pH, gas bubble size, airflow rates, and fractionator geometry. Predictive relationships were developed to describe these effects and are considered generally applicable to predict the foam enrichment process. Predicting the actual operation of a specific foam fractionator requires additional mathematical expressions to model the foam collection process and removal from the top of the water column. Here, the geometric characteristics and type of foam removal device or geometry of placement become important. Performance data in the literature was used in coajunction with a mathematical model that predicted foam enrichment to model the foam collection process for a typical foam fractionator design. This overall model can be used for foam fractionators that employ glass bonded air diffusers with an inverted funnel at the top of the fractionator column to concentrate and remove the foam being produced. An example problem is given to demonstrate the utility of the mathematical models. Since foam fractionators are typified by erratic performance, the mathematid models presented must be used with some caution and only viewed as providing estimates of average fractionator performance.

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00250.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe objective of this project was to develop a vision system that could predict when crawfish will molt. Different sections of the crawfish shell were examined to determine how the color changed as the time of molting approached. A strip on the tail section of the crawfish showed the greatest, most consistent color change. The average red/green × red/blue ratio decreased for every crawfish as the molting time approached. Using this ratio as a predictor, it was possible to predict the molting of a crawfish within 3 d with an accuracy greater than 80%. The limitation on accuracy was primarily the result of the large variations in natural shell color among the crawfish

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00251.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAmerican shadAlosa supidissimabroodstock were collected from the Susquehanna River during their spawning migration. Mean volume of expressible milt (± standard deviation) was 2.5 (±1.7) mL/kg body weight; mean spermatozoid count was 66.2 ± 109(±163 ± 109) spermntozoa/mL; and duration of 50% motility was 36.5 (±10.3) see. Ovarian biopsies indicated the presence of oocytes of various sizes (200–2,000 μm in diameter) and stages of development. Fish were implanted with a delivery system loaded with gonadotropin‐releasing hormone analog (GnRHa) and started spawning 2 d after treatment. Fertile eggs were collected daily for the next 9 d, for a total of 50,100 eggs/kg body weight with a mean fertilization success of 62%. Upon cessation of spawning, the ovaries of all females still contained large numbers of oocytes at various stages of development, as at the beginning of the experiment, but with a greater number of atretic oacytes. Our observations show that American shad have an asynchronous ovarian development, and treatment with a GnRHa delivery system is effective in inducing several successive spawns of fe

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00252.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe gametogenic cycle of the white bassMoronc chrysopswas characterized for one year at monthly intervals by measuring circulating levels of the sex steroid hormones testosterone (T) and 11‐ketotestosterone (11‐KT) in males, and 17β‐estradiol (E2) and T in females. Vitellogenin (VTG), the egg yolk precursor, was also measured in female blood plasma. Gonadal status of individual fish was assessed by histological evaluation, measurement of oocyte diameters, and spermintion response. At the onset of vitellogenesis (October), blood plasma levels of E2and T were low, but increased significantly as the spawning period (March‐April) approached and oocytes attnined their maximum diameter. All stages of oocyte development were observed in mature females, indicating that the white bass is a multiple‐clutch, groupsynchronous spawner. Androgen levels increased in males throughout the reproductive cycle and reached maximal levels during the spawning period. The increase in androgens coincided with sperm production and spermintion in males. The circannual endocrine and gonadal development patterns observed in white bass were similartothose of other members of g

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00253.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractReproductive performance was evaluated for sexually mature malePenueus vannameifed one of four diets: 1) commercial 40% protein shrimp growout diet; 2) 100% squid; 3) 50% squid, 25% bloodworms and 25%Artemia;and 4) starvation. Spermatophores were ejaculated manually from tagged males at stocking and every 12 d thereafter. For each half of the compound spermatophore, weight and sperm count were determined. Four methods were used to assay the sperm quality: 1) gross morphology (GM); 2) trypan blue stain (TB); 3) acridine orange stain (AO); and 4) egg water induced reaction (EW). The reaction induced whenP. vannameisperm are exposed to conspecific egg water is grossly similar to that observed in vivo at the surface of the freshly spawned eggs from naturally mated females. Little correlation was found between spermatophore weight and sperm count. The best correlation was found between GM and AO (r2= 0.859,P<0.01). Many morphologically abnormal sperm did not stain with TB. For most of the spermatophores evaluated; over 80% of the sperm were morphologically normal, were unstained with TB, and were immediately fluorescing light green when stained with AO. When exposed to egg water, sperm from these apparently good quality spermatophores yielded mixed results. The analysis of dietary effects on spermatophore quality were equivocal. Although a significant decline in body weight, spermatophore weight, and sperm count were observed in the starvation treatment as compared to maturation and squid diets, no significant differences were observed in MY of the sperm quality assays.

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00254.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractSix species of tropical sea cucumbers (Echinodermata) of high to moderate commercial value were evaluated as to their potential for being propagated asexually by induction of transverse fission. The species considered wereThelenota ananas, Holothuria fuscogilva, Actinopyga mauritiana, A. miliaris, Stichopus chloronotus, andS. variegatus. Rubber bands placed midbody on the sea cncumbers provided an effective yet simple technique to induce transverse fission. Although fission could be induced in all six species, onlyT. ananasandS. chloronotushad the ability to regenerate both anterior and posterior parts into whole animals. Other species showed no or low potential for regeneration (H. fuscogilva, A. mauritiana) or regeneration of only the posterior part into whole animals (S. variegatus, A. miliaris). BothT. ananasandS. chloronotushad survivorship of nearly 80% or greater.S. chloronotusregenerated anterior and posterior parts into whole animals within 3 mo. In contrast,T. ananasregenerated the posterior part into a whole animal within 5 mo while the anterior part was regenerated within 7 mo. Consequently, weight recovery began earlier withS. chloronotusrelative toT. ananas.

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00255.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThreonine is an indispensable amino acid required by all animals for normal growth and metabolic functions. An experiment was conducted in a brackish water (5 ± 1 ppt) recirculating system to quantify the minimum dietary threonine requirement of juvenile red drumSciaenops ocellatus. The experimental diets contained 350/0 crude protein from red drum muscle and crystalline amino acids and 3.2 kcal available energy/g diet. Incremental levels of L‐threonine were added to the diets and fed to juvenile red drum initially averaging 2.8 g/fish for 8 wk. Weight gain and feed efficiency of fish fed the various diets were significantly (P<0.05) affected and increased linearly as dietary threonine increased until plateauing around 0.8% of dry diet. Protein efficiency ratio and protein conversion efficiency values for fish fed the different diets also were significantly affected by threonine level and indicated requirement values of 0.8–0.9% of dry diet. Free threonine in plasma also significantly responded to increasing dietary threonine but indicated a slightly higher requirement value of approximately 1.0% of dry diet. Based on these data, the minimum threonine requirement of juvenile red drum was determined to be approximately 0.8% of dry diet (2.28% of dietary protein). This requirement level is similar to values reported for some other fish species. Based on this information diets may be formulated more precisely for aquacultural production of red

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00256.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractChemical budgets were determined for nitrogen, phosphorns, dissolved oxygen and chemical oxygen demand for three 0.1‐ha earthen ponds stocked withOnwchrornis nilotieusat the El Carao National Fish Culture Research Center, Comayagna, Honduras, for two 150‐d culture periods, corresponding to the rainy and dry seasons. Layer chicken litter was added to ponds weekly at 500 kg dry matter/ha. Concentrations of nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) in pond water increased during each season. No significant seasonal differencea in concentrations of water quality variables were observed. Chicken litter added to ponds represented 92–94% of N input, 93–95% of P input, and 43–52% of COD input. Photosynthesis by phytoplnnkton provided 47–56% of COD and 98% of dissolved oxygen (DO) added to ponds. Net inward diffnsion of oxygen added 1.2–1.5% of total DO. Regulated inflow was a minor source of nutrients, and contributed 3–4% of input N, 3–4% of input P, 1% of COD input, and 1% of DO input. Nutrient inputs from rain were ≤1% of total for each nutrient. Fish harvest accounted for 18–21% of total N, 16–18% of total P and 2% of COD added to ponds. Community respiration accounted for 48–57% of COD and 99.5% of DO added to ponds. Nutrient losses in pond effluent at draining were: 7–9% of total N, 29–37% of total P and 2–3% of COD. While measured gains exceeded measrued losses, significpntly greater N, P and organic matter concentrations in pre‐drain samples indicated pond mud was a major sink for added nutrients, accumulation in mud represented 70% of total N, 35

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00257.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractOff‐flavor problems in farm‐raised catfishIctalurus punctatusincrease production costs and pose inventory management problems for catfish farmers. Multiperiod mathematical programming techniques were used to test the effect of 16 different off‐flavor scenarios on expected net returns above variable cost with and without cash flow restrictions. The patterns of off‐flavor incidence had less effect on farm profits than whether or not fish are off‐flavor during certain key months of the year. To be feasible, systems designed to purge off‐flavor from catfish would need to cost less than $0.05 to $0.06/kg (if cash flow is not a consideration) or $0.04/kg to $0.25/ke (with cash flow cons

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00258.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe antimicrobial enrofloxacin (Baytril®, Bayer) was evaluated under field conditions in the winter months for treatment of clinicalAeromonas salmonicidainfections in salmonids by feeding medicated diets. Two trials in which lake troutSalvelinus namaycushwere treated with enrofloxacin at 10mg/kg per d for 10d resulted in reduced mortalities when compared to non‐medicated controls. A third trial in which Atlantic salmonSalmo salarwere treated required 20d for the fish to consume the 10d medicated ration, due to poor feeding. This resulted in an effective dose of 5mg/kg per d for 20d. In spite of the lower feeding activity, a reduction in mortalities in medicated fish was observed. Tissue concentrations of drug were in excess of minimum inhibitory concentrations of the drug for theA. salmonicidaisolates test

ISSN:0893-8849    

DOI:10.1111/j.1749-7345.1995.tb00259.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY