Ronald P. Phelps

The effect of manures and chemical fertilizers on the production of Oreochromis niloticus in earthen ponds

Abstract The effect of weekly applications of similar quantities of nitrogen and phosphorus from three different sources on the production of Oreochromis niloticus (10 000/ha) was studied in 0.1-ha earthen ponds. Layer chicken litter (500 kg total solids (TS)/ha), dairy cow manure (1020 kg TS/ha) and chemical fertilizer (46-0-0 at 30.6 kg/ha and 0-46-0 at 62.6 kg/ha) were applied weekly. Mean total net production after 150 days was greater with chicken litter (1759 kg/ha). Differences in fish production were explained in terms of net and gross primary productivity and community respiration.

Egg and larval quality of natural and induced spawns of red snapper, Lutjanus campechanus

Egg and larval quality of red snapper, Lutjanus campechanus from natural spawns of domesticated brooders and hormone-induced spawns of wild fish were compared. Eggs and larvae from natural spawns were found to be more viable in terms of fertilization, hatching and survival rate. Also, eggs from natural spawns were larger, and eggs and recently hatched larvae had larger oil-globule. These findings indicate that natural spawning of red snapper can be a sustainable and reliable source of good quality eggs.

Effects of initial age and size on sex reversal of Oreochromis niloticus fry using methyltestosterone

Abstract The influence of age and size of Oreochromis niloticus fry at the initiation of hormone treatment on production of phenotypic male populations was investigated. A population of fry was divided into two lots. The first (Age I) was graded into four size categories: 11 mm and less, 12–13 mm, 14–16 mm, and greater than 16 mm total length. The second lot (Age II) was held an additional 10 days then graded into the same size categories. All groups were given methyltestosterone at 60 mg per kg of feed for 28 days. Initial size was a more significant factor than age in affecting the percentage of phenotypic males observed. The duration of hormone treatment while fry were less than 18 mm length was significantly related to the percent males obtained, fish receiving less than 14 days of treatment had a lower percentage of males.

Hydrology of fish culture ponds in Gualaca, Panama

Abstract During 1985, rainfall, evaporation and seepage were measured in 12 experimental fish culture ponds at the Gualaca Freshwater Aquaculture Research Station, Gualaca, Panama, to provide baseline pond hydrology data for the area and a water budget for the station. Mean monthly rainfall ranged from 0 to 27 mm day −1 , while pond evaporation ranged from 1·4 to 8·4 mm day −1 . An equation was developed to predict pond evaporation from solar radiation measured by photometry. Among the 12 ponds, mean seepage ranged from 19 to 58 mm day −1 and averaged 31. Seepage accounted for 87% of water lost from the ponds. A regression equation was developed to predict the quantity of water gained by runoff into ponds during rainfall. Monthly water balances (mm day −1 ) for the station ranged from −39 to 14 and averaged −13. Water deficits occurred during 9 of 12 months. The annual water deficit could be reduced to zero should seepage be reduced by 66%. Particular attention needs to be given to pond construction on kaolinitic soils, which although high in clay, may be very porous.

Sex reversal in black crappie Pomoxis nigromaculatus: effect of oral administration of 17α-methyltestosterone on two age classes

The masculinizing effect of 17α-methyltestosterone (MT) on two age classes of black crappie Pomoxis nigromaculatus was investigated. Broodstock were induced to spawn by intramuscular injection of human chorionic gonadotropin hormone (hCG). Fry produced were divided into two age classes, age I (40 days old), and age II (60 days old). Age I fry were fed to satiety with feed containing MT at a concentration of 0, 30, or 60 mg/kg feed. Age II fry were fed MT at 60 mg/kg feed only. Both age classes were fed hormone treated diet for 30 days. Mean initial weight and length of age I fry were 0.21 ± 0.15 g and 23 ± 2.2 mm, respectively (mean ± SD), whereas age II fry were 0.22 ± 0.10 g and 24 ± 3.4 mm, respectively. Age I fry fed with 60 mg MT/kg feed yielded the highest (90%) mean percent males relative to all treatments (P < 0.01). Age I fry fed with 30 mg MT/kg feed produced 71% mean percent males that was significantly higher (P < 0.05) than age II fry fed with 60 mg MT/kg feed, and fry fed with control diet (P < 0.01). There was no significant difference in percent males between age II fry (58%) and control (51%). Two patterns of ovotestis were identified by histological examination. One pattern was dominated by ovarian tissue or Ovotestis-Mainly Testicular (OTMO), the other was dominated by testicular tissue or Ovotestis-Mainly Testicular (OTMT). Sex reversal in black crappie seems to be influenced by age more than size. This study reports the first successful masculinization of this species by hormonal treatment.

Response of tilapia yield and economics to varying rates of organic fertilization and season in two Central American countries

The response of Nile tilapia (Oreochromis niloticus) yield to weekly applications of chicken litter at 125, 250, 500 or 1000 kg total solids (T.S.)/ha was determined in Honduras and Panama using a completely randomized design. Tilapia were stocked at 10 000/ha into 0.1-ha (Honduras) and 0.087-ha (Panama) earthen ponds. Each experiment, which lasted approximately 150 days, was performed during the rainy and dry season. Enterprise budgets were developed for each fertilization rate in each country. Gross yield of tilapia (y) increased significantly with chicken litter applications (x) in both countries, and was described by the model y=797.3+2.945x−0.001x2 (r2=0.775; n=48). Gross yields ranged from 827–2729 kg/ha in 147 days during the rainy season, and from 1145–2984 kg/ha in 150 days during the dry season. Maximum tilapia gross yields were achieved at 1000 kg T.S./ha week−1 chicken litter in both countries. In Honduras, rainy (1761 kg/ha in 152 days) and dry (1705 kg/ha in 150 days) season mean tilapia gross yields were similar (P=0.05). Dry season (2071 kg/ha in 149 days) mean tilapia gross yield in Panama was significantly greater (P<0.05) than rainy season mean gross yield (1683 kg/ha in 141 days). Rainy season climatic conditions in Panama probably contributed to the lower fish yields. Mean fish gross yield at the cooler, drier Honduras site (1733 kg/ha in 151 days), an upland valley located 580 m above sea level, and at the Panama site (1855 kg/ha in 145 days), a coastal plateau 100 m above sea level, was similar (P=0.05). Mean gross yields were similar in both countries for all but the highest fertilization rate, where the Panama mean yield was significantly greater. This difference was caused by site-specific factors other than nutrient input. The use of chicken litter as an organic fertilizer was profitable in both Honduras and Panama. Net returns to land, labor and management during the 5.5-month production cycle ranged from

Production of Gulf Killifish in the Black Belt Region of Alabama Using Saline Groundwater

642 to

Influence of site and season on water quality and tilapia production in Panama and Honduras

1724/ha (Honduras) or from −

Effect of Sea Salt on the Hatching of Channel Catfish Eggs

237 to

Evaluating the Benefits of Size-Sorting Tilapia Fry Before Stocking

313/ha (Panama) for the low to high fertilization rates, respectively. Application of 1000 kg T.S./ha week−1 chicken litter yielded the greatest estimated profit in both countries.