David Teichert-Coddington

Lack of Response by Tilapia nilotica to Mass Selection for Rapid Early Growth

Abstract Mass selection for rapid and slow early growth was applied for one generation to 58-d-old Nile tilapia Tilapia nilotica (Ivory Coast strain). Realized heritability (±SE) for rapid growth was –0.10 ± 0.02, and mean body weight of progeny was not different (P > 0.05) from that of control fish. This confirms an earlier prediction from half-sib analysis of the same stock that selection for rapid growth would be ineffective for these fish (half-sib heritabilities were 0.04 ± 0.14 at age 45 d and 0.04 ± 0.06 at age 90 d). In contrast, selection for slow early growth resulted in realized heritability of 0.36 ± 0.08, and mean body weight of progeny was less than that of control fish (P < 0.05). Our study indicated that an upper limit to growth enhancement by selection exists in this stock of T. nilotica, probably due to a small founder stock, subsequent reductions in effective breeding numbers, and 8 years of domestication. We conclude that half-sib analysis can be an efficient means for estimating the e...

Treatment of harvest discharge from intensive shrimp ponds by settling

Abstract Effluent from intensively managed shrimp ponds was examined during harvest when ponds were drained. Concentrations of nutrients and solids in effluents were significantly higher during the final 20 cm of discharge (16% of pond volume), but greatest increases occurred during the final 5 cm of discharge (3.9% of pond volume). When the final 20 cm of pond discharge was allowed to settle, near maximum sedimentation for most variables occurred within 6 h. Settling removed total nitrogen less effectively than other nutrients. Within 6 h, 100% of settleable solids, 88% of total suspended solids, 71% of volatile solids, 63% of biochemical oxygen demand (BOD), 31% of total nitrogen and 55% of total phosphorus had sedimented from the final 20 cm of effluent. For the total pond this represented 61% settleable solids, 40% total suspended solids, 24% total volatile solids, 12% BOD, 7% total nitrogen, and 14% total phosphorus. Of the total amount removed during settling, 61% of settleable solids, between 18 and 26% of BOD, nitrogen and phosphorus, and between 34 and 45% volatile and suspended solids were found in the final 20 cm of discharge (16% of pond volume). A simple treatment of pond effluents at harvest can be effected by shunting the last 10–20% of discharge through a settling pond with no more than 6-h of residence.

Partial nutrient budgets for semi-intensive shrimp farms in Honduras

Shrimp farms in Latin America typically have relatively low stocking rates and are managed without aeration. Nutrient budgets for these farms have not been well established. Intake and discharge from 21 ponds on six shrimp farms located on estuaries or embayments of the Gulf of Fonseca in Honduras were characterized during rainy and dry seasons. Mean shrimp stocking rate, yield, and feed conversion ratio (FCR) for these ponds were 8.2/m2, 633 kg/ha, and 2.74, respectively. Mean intake values of soluble reactive phosphate (SRP), dissolved inorganic nitrogen (DIN), total nitrogen (TN), total phosphorus (TP) and BOD5 were significantly higher in estuaries than in embayments during both seasons. Water exchange produced a mean net discharge of TN, TP, BOD5, chlorophyll a, COD, total alkalinity and salinity, and a mean net intake of DIN; mean SRP was practically equal in discharge and intake water. Each kilogram of feed nitrogen and phosphorus applied to ponds resulted in 0.21 kg of net nitrogen discharge and 0.16 kg of net phosphorus discharge by water exchange. Use of inorganic fertilizers promoted net discharge of phosphorus and nitrogen. Net nitrogen discharge by water exchange significantly increased as nitrogen input by feed increased (P<0.01). Ponds gained nitrogen primarily from intake water (63%) and feed (36%), and nitrogen was lost primarily from water exchange (72%) and harvested shrimp (14%). Ponds gained phosphorus mostly from intake water (51%) and feed (47%), and phosphorus was lost primarily from water exchange (56%) and harvested shrimp (9%). About 7% of input nitrogen and almost a third (31%) of input phosphorus were not accounted for in measured losses, and presumably were fixed or metabolized in ponds. Mean conversion of feed nitrogen and phosphorus to shrimp flesh averaged 41% and 20%, respectively. Each kilogram of shrimp production resulted in 16.8 g of net nitrogen loss and 2.3 g of net phosphorus loss by water exchange.

Texture and chemical composition of soils from shrimp ponds near Choluteca, Honduras

Analyses of bottom soils from three recently-established (newer) and three older ponds on each of two, semi-intensive shrimp farms near Choluteca, Honduras, revealed that the 0 to 2.5 cm layer had greater concentrations of most variables than deeper layers. Concentrations of total carbon, nitrogen, sulphur, phosphorus, calcium, iron, manganese, and zinc were greater in older than in newer ponds on one or the other of the farms. After 8–11 y of continuous production, total carbon concentrations varied over pond bottoms, and concentrations usually were greatest (1.5–2.5%) in inlet sections. Nitrogen concentrations were about 20% those of carbon and changes in nitrogen concentration closely followed those of carbon. Precipitation of iron pyrite (FeS2) in anaerobic soil layers was the apparent cause of sulphur accumulation in older ponds. Phosphorus accumulated in older ponds on the farm where heavy doses of fertilizer were applied. Soils of both older and newer ponds on both farms had large accumulations of major cations, a large portion of which were water-soluble salts. There was no evidence of development of adverse soil quality in older ponds.

Effects of Urea Application, Aeration, and Drying on Total Carbon Concentrations in Pond Bottom Soils

Abstract Aerated ponds did not accumulate as much carbon in bottom soils as control ponds. Application of urea to manured ponds did not accelerate carbon loss from bottom soils. When ponds were drained for fish harvest, appreciable carbon was eroded from the surface layers of bottom soil. Further decomposition of soil carbon occurred during the 5-week drying period between crops. Within-pond variation in soil carbon concentration was high; a technique for selecting replication and sample size requirements for experiments on changes in bottom soil carbon concentration is provided.

Higher minimum dissolved oxygen concentrations increase penaeid shrimp yields in earthen ponds

Abstract Nine 0.11-ha earthen ponds were stocked on 15 May 1997 with Litopenaeus vannamei and L. stylirostris postlarvae in similar proportions at a total density of 33 animals/m 2 . Ponds were equipped with automated temperature and dissolved oxygen (DO) concentration data acquisition devices that sampled ponds every 30 min. Aspirator-pump aerators (0.75 kW) were automatically activated when DO fell to 65% (4.6 mg/l at 29°C and 15 ppt salinity), 40% (2.8 mg/l at 29°C and 15 ppt), or 15% (1.1 mg/l at 29°C and 15 ppt) of saturation. Mean shrimp yield, survival of both species, and profitability increased linearly as minimum DO concentration increased from 15% to 65% of saturation ( P P >0.05).

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.

Relationship between wind speed and reaeration in small aquaculture ponds

Abstract Two 1000 m2 ponds at the El Carao National Aquaculture Center at Comayagua, Honduras were deoxygenated by treatment with sodium sulfite and cobalt chloride, and biological activity was suppressed by formalin and copper sulfate application. Wind speed and the change in dissolved oxygen concentration were monitored with a data logger system during reaeration period. Standard oxygen transfer coefficients were related to wind speed measured at 3-m height by the equation: K L a 20 =0·017x − 0·014; r 2 =0·882 where KLa20 = standard oxygen transfer coefficient at 20°C (h−1) and X = wind speed (m s−1). A method for computing pond reaeration rate from the standard oxygen transfer coefficient is presented.

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

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

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