Hapa Nets Research Articles

Effects of Cleaning Interval, Hapa Layers and Stocking Density on Growth Performance of Sandfish Holothuria scabra Juveniles in Ocean‐Based Nursery Production Systems

ABSTRACTThe mass production of release‐size H. scabra juveniles in the Philippines is primarily done in a floating hapa ocean‐based nursery systems. To optimize its production, understanding the influence of different culture conditions and their management is necessary. In this study, the effects of hapa net cleaning interval, hapa layers, and stocking density on growth and survival of sandfish juveniles reared in floating hapa (L × W × H: 1.7 m × 0.9 m × 1.2 m) nursery system were assessed in two 60‐day field studies. Results showed that the number of hapa net layers and cleaning interval had negligible effects on the growth performance of sandfish juveniles by day 30. However, sandfish juvenile survival was affected by hapa net layers with higher survival in triple‐layer mosquito net hapas (40.5 ± 0.97%) compared to double‐layer mosquito net hapas (17.8 ± 0.62%). By day 60, the growth performance of sandfish juveniles in double‐layer hapas was higher (average weight: 5.0 ± 0.97 g; AGR: 0.13 ± 0.03 g day−1) compared to that in triple‐layer mosquito hapa nets (average weight: 3.1 ± 0.23 g; AGR: 0.07 ± 0.01 g day−1). Survival of sandfish juveniles reared in double‐layer mosquito net hapas, cleaned at 5‐day intervals (85.9 ± 4.58%) was significantly lower compared to all other treatments. Conversely, initial juvenile stocking density did not significantly affect the growth performance and survival of sandfish juveniles in both rearing cycles. We therefore recommend the use of triple‐layer mosquito net hapas during the first 30‐day culture period and an initial stocking density of 1000 post‐settled sandfish juveniles to increase production output. After 30 days, when the juveniles are larger, the use of double‐layer mosquito net hapas and lower stocking density are recommended to reduce cost and enhance growth performance. Where cleaning is necessary, hapa nets may be cleaned at 10‐day intervals to improve survival. The results of this study have important implications for optimizing the production of release‐size sandfish in ocean‐based nursery systems in the Philippines.

Effects of processed duckweed (Lemna paucicostata) meals as protein sources in Oreochromis niloticus (Linnaeus, 1758) diets

Effects of processed duckweed meals as a replacement for toasted soybean meal in the diets of Oreochromis niloticus fingerlings were evaluated. Sun-dried and blanched duckweed meals were used to replaced toasted soybean meal in at 25, 50, 75, and 100% each. Feed Solution Software (version 2022) was used to formulate nine iso-nitrogenous diets at 32% crude protein. 27 Hapa nets of 1 m2 each were used for the feeding trials for six months. Ten fingerlings of Oreochromis niloticus were stocked per Hapa and fed 5% body weight three times per day. The best mean weight gain (460.59 g), viscerosomatic index (9.90) and feed conversion ratio (1.82) were recorded in the fish fed 75% blanched duckweed meal while the fish fed 100% sun-dried duckweed meal and 100% blanched duckweed meal recorded the poor mean weight gain, viscerosomatic index and feed conversion ratio of 401.69 g and 394.03 g, 6.49 and 6.36, 2.06 and 2.10, respectively. The cost-benefit evaluation revealed that 75% blanched duckweed meal gave the highest net profit (₦3,682) and lowest incident cost (₦6.49). This study revealed that soybean meal can be replaced with 75% blanched duckweed meal in the diet of Oreochromis niloticus without any inauspicious effects on the growth and nutrient utilization, and will reduce the cost of production and maximize profit.

Functional Effects of Hydrolyzable Tannins on the Growth, Health Status, and Hepatopancreas Histology of Pacific White Shrimp Penaeus vannamei Reared under Commercial Pond Conditions

In the present study, the functional effects of hydrolyzable tannins (HT) extracted from the sweet chestnut tree Castanea sativa were evaluated either by directly incorporating them into the diet or by using a top-dressing application on the growth, body composition, total hemocyte counts, lysozyme activity, and histomorphological condition of the hepatopancreas of Pacific white shrimp Penaeus vannamei. Shrimp was confined in hapa nets installed within commercial outdoor ponds for 90 days. Eight experimental diets included a basal formulated diet (BD) with varying inclusion levels of HT (BD-0%, BD-0.1%, BD-0.2%, and BD-0.3%), a low fish meal (FM) diet with reduction on the inclusion level of FM from 10% to 7.5% and labeled as LFM 0.3% HT, a top-dressing HT application (TC) on basal diet (BDTD-0.4% HT), and a commercial diet (CDTD-0% HT and CDTD-0.4% HT). The final body weight (FBW), percentage weight gain (PWG), thermal growth coefficient (TGC), average daily growth (ADG), and feed conversion ratio (FCR) were significantly better in the group of shrimp fed with BD-0.3% HT compared to BD-0% HT. The administration of CD-0.4% HT was able to enhance the growth performance of shrimp compared to BD-0% HT and CD without HT. Higher protein and fat contents were found in the body of shrimp fed with graded levels of HT compared to shrimp fed with BD or CD without HT. Numerically, the direct inclusion and top-dressing process of HT increased the total hemocyte count and lysozyme activity in shrimp. Both BDTD-0.4% HT and CDTD-0.4% HT were also able to support a better hepatopancreatic condition with reference to histomorphology and integrity. These results indicated that BD-0.3% HT inclusion could significantly improve the growth performance and prevent the alteration in health and histomorphological condition of the hepatopancreas of shrimp P. vannamei cultured in hapa nets under commercial farm conditions, but also 0.4% HT could be used as a supplementation dosage for the top-dressing process in diets.

Census of potential predators and competitors of sandfish, Holothuria scabra, juveniles during floating hapa ocean nursery culture

AbstractPredation and competition are among the most important factors affecting sandfish, Holothuria scabra, growth and survival in ocean‐based production systems. In this study, the potential predators and competitors of sandfish juveniles reared at two sites in the Philippines using the floating hapa ocean nursery system were assessed. A total of 26 species of potential predators and competitors from 16 different families of fishes, molluscs and crustaceans were recorded. These taxa were dominated by the opisthobranch Stylocheilus striatus at Bolinao (north–west Luzon) and the isopod Cymodoce sp. at Maliwaliw (eastern Visayas). Highest number of potential predators and competitors that recruited and/or migrated to the inside of floating hapa nets was recorded on day 23 at Bolinao and day 30 at Maliwaliw, then decreased over the 69‐day duration of the study. Mean length, absolute growth rates (AGRs) and survival of sandfish juveniles reared in floating hapas at the two sites varied during the study. AGRs were highest at 1.17 ± 0.06 mm day−1 at Bolinao, and 1 ± 0.08 mm day−1 at Maliwaliw, by days 23 and 60, respectively. Mean lengths of sandfish juveniles reared at Bolinao and Maliwaliw by the end of the study were 46.7 ± 0.15 and 58.8 ± 2.4 mm, respectively, and survival at both sites was high at 96% by the end of the study. Negative correlations were observed between the number of individual predators and competitors, and survival and growth rates of sandfish juveniles reared at Bolinao and Maliwaliw, respectively. Our results highlight the importance of predator and competitor management measures and appropriate site selection to optimize growth performance and survival of sandfish juveniles reared in ocean‐based culture production systems.

Digestibility, Growth and Hepatosomatic Index of Oreochromis Niloticus (Linnaeus, 1758) Fed Diets Containing Blanched Lemna paucicostata (Hegelm)

This study evaluated digestibility, growth and hepatosomatic index of Oreochromis niloticus fed diets containing blanched Lemna paucicostata as a replacement for toasted soybean meal. Five iso-proteinous diets were formulated using feed solution software, blanched Lemna paucicostata was used to replace toasted soybean meal progressively at 0%, 25%, 50%, 75% and 100% respectively. Fifteen Hapa nets of 1m2 each were used. Ten Oreochromis niloticus juveniles were introduced into each of the nets. The fish were fed at 5% body weight three times daily for a period of six months. There was significant difference (P≤0.05) in the apparent protein digestibility coefficient among the treatments and the control. Highest apparent protein digestibility coefficient of 92.94% was recorded in the diet containing 75% blanched L. paucicostata meal while the least value of 86.86% was obtained in the diet with 100% L. paucicostata meal. The fish fed diet containing 75% blanched L. paucicostata meal recorded significantly highest (P≤0.05) mean final weight of 468.01g followed by the fish fed with 50% blanched L. paucicostata meal with 453.68g, the fish fed 100% blanched L. paucicostata meal recorded significantly lowest (P≤0.05) value of 401.54g. The fish fed diet containing 75% inclusion level of blanched L. paucicostata meal gave the best protein, lipid, ash and carbohydrate digestibility of 92.94%, 90.62%, 52.29% and 80.56%, respectively and also gave the best growth performance and hepatosomatic index.

Growth Performance and Nutrient Utilization of Nile Tilapia (Oreochromis niloticus) Fed Processed Duckweed (Lemna paucicostata) Meal as Protein Source

Growth performance and nutrient utilization of Nile tilapia (Oreochromis niloticus) fed processed duckweed (Lemna paucicostata) meal were evaluated. Blanching and sun-drying were employed as the processing methods. The blanched and sun-dried duckweed meals were used to replace toasted soybean meal in the diets of Nile tilapia at 25%, 50%, 75%, and 100% each. Nine iso-proteinous diets were formulated using the least cost feed formulation software. The feeding trials were conducted in 27 Hapa nets measuring 1m2 each for 24 weeks. Ten fingerlings of Nile tilapia were stocked per Hapa and fed three times daily at 5% biomass. The fish fed 75% blanched duckweed meal had the best mean weight gain (460.59g), feed conversion ratio (1.82) and protein efficiency ratio (12.67) while the fish fed 100% inclusion level of sun-dried duckweed meal and 100% of blanched duckweed meal diet had the poor mean weight gain, feed conversion ratio and protein efficiency ratio of 401.69g and 394.03g, 2.06 and 2.10, 11.05 and 10.37, respectively. This study revealed that blanched duckweed meal can replace toasted soybean meal in the diet of Nile tilapia at 75% without any unpropitious effect on the growth performance and nutrient utilization.

Kinerja Pertumbuhan Benih Ikan Lele (Clarian gariepinus) Yang Diberi Prebiotik Ekstrak Umbi Sarang Semut (Myrmecodia pendans) dan Probiotik Lacticaseibacillus paracasei

This study aimed to evaluated the growth performance of dumbo catfish (Clarias gariepinus). In this study, ant nest tuber extract and probiotic Lacticaseibacillus paracasei were mixed into feed with the coated method without the addition of ant nest tuber extract and probiotic Lacticaseibacillus paracasei (A), 1% ant nest tuber extract (B), probiotic Lacticaseibacillus paracasei 1% (C). and a combination of ant nest tuber extract and probiotic Lacticaseibacillus paracasei each 1% (D). Fish with an initial body weight of 1.5 - 2 g were kept in 3 ponds (15x10x1.5) m3 with a total of 12 hapa nets measuring 1x1x1 (m3) (45 fish / hapa nets). Fish were fed treatment with three replications for 35 days. The best feed efficiency, feed conversion ratio, daily growth rate and absolute weight growth were found in the African catfish fry group that consumed a combination of feed supplementation with 1% dose of ant nest tuber extract and 1% dose of probiotic Lacticaseibacillus paracasei, each of 185.47%. , 0,55,7,79%, and 20,80 gr

Sex reversal dynamics of Nile Tilapia (Oreochromis niloticus) and impact on growth performance

AbstractNile Tilapia (Oreochromis niloticus) is one of the most economically important freshwater aquaculture species globally. However, reproduction during grow-out is a major problem that hinders fish growth. Therefore, production of all-male populations of tilapia has been developed to address the problem and is also identified as one of the most effective techniques of increasing tilapia growth. Various methods have been used to produce all males in Nile Tilapia i.e. use of hormone treatment (17- α-methyltestosterone), use of temperature shock and the recent YY technology. The latter two methods have limited documentation and usage in Kenya. The current study compared effectiveness of temperature and hormone sex reversed O. niloticus fry and influence on growth in hapa nets over a period of 3 months. Nile Tilapia fry of 3 days old after egg yolk absorption were sex reversed using hormone for 21 days and temperature shock for a period of 14 days. Hormone use involved making a dose of 60 mg kg-1 of feed while temperature shock involved raising temperature from 28°C to between 30 °C and 34 °C. Analysis of Specific Growth Rate using one-way analysis of variance, ANOVA, showed no significant difference between hormone and temperature induced sex reversed fish (F = 0.0975, P = 0.7705). Sex reversal efficacy rates of 91.18% and 92.86% were attained using 17- α-methyltestosterone hormone and temperature shock, respectively. The results indicate that temperature shock could be a replacement for Tilapia sex reversal without any negative consequences on growth.

Dietary incorporation of Sweet Potato Ipomoea batatas shoots improved growth performance and haematological profile of Tilapia Oreochromis niloticus in Hapa Nets

This study was conducted to evaluate the potential of sweet potato Ipomoea bata-tas powder (IbSPP), hot-water extracts (IbSPHWE) and crude ethanolic extracts (IbSPCEE) as growth pro-moter and immunoenhancer for tilapia cultured in hapa nets. Fish were divided ran-domly into four Treatments: T1 (control group) was fed a practical diet (PD) while T2, T3 and T4 were fed PD + IbSP powder (P), PD + IbSP hot-water extract (HWE), PD + IbSP Crude Ethanol Extracts (CCE), respective-ly. The growth indices and haematological profile of cultured fish were recorded after four months of feeding experiment. The final weight, weight gain, specific growth rate, condition factor, FCR, PER, FER were significantly higher in fishes that re-ceived PD +IbSPHWE than those that received either PD, PD + IbSPCEE or PD+ IbSPP only. The same trend was observed with the RBC, Hb, HCT, WBC and the PLT and its indices. The study has demonstrated that in-corporation of the hot-water extracts of I. batatas could improve the growth perfor-mance and increase immu-nocompetence of O. nilot-icus as evidenced by im-proved haematological pro-file.

Growth performance and economic viability of dietary inclusion of Ipomoea batatas L. shoot powder and extracts in the practical diets of Oreochromis niloticus L.

The study aims to determine the growth performance and economic viability of the dietary supplementation of camote i.e., Ipomoea batatas L. powder and extracts in the diets of the Nile tilapia. The fish were reared in twelve 1 m3 hapa nets installed in a 500 m2 pond. Four groups of fish were used in the experiment; the control group was fed with formulated practical diets (PD), and diets supplemented with either camote shoot powder (PD + CSP), hot-water extract (PD + CSHWE), and crude ethanol extract (PD + CSCEE). The feeding trial lasted 12 weeks. The weight gain (WG), feed conversion ratio (FCR), feed efficiency ratio (FER), protein efficiency ratio (PER), specific growth rate (SGR), and condition factor (CF) were studied. The economic viability was determined through the cost of production, gross profit, cost-and-return, and profitability analyses. The fish fed with PD + CSHWE exhibited improved growth performance as evidenced by an increase in WG, FER, PER, SGR, and CF, while showing low values of FCR. The economic analyses also revealed that PD + CSHWE was the most economically feasible diet based on the cost of production, gross profit, cost-and-return, and profitability analyses. The study had proven that the incorporation of CSHWE in practical diets could improve the growth performance and increase profitability if used for tilapia culture.

Growth performance and survival rates of Nile tilapia (Oreochromis niloticus L.) reared on diets containing Black soldier fly (Hermetia illucens L.) larvae meal

Abstract A 72-day feeding trial was conducted at Sagana fish farm to assess the effects of substitution of fish meal (FM) with black soldier fly larvae meal (BSFLM) on the growth performance and survival rates of Nile tilapia. Four test diets were formulated and substitution of FM by BSFLM made at 0%, 33%, 67% and 100%. 240 male Nile tilapia (52.3 ± 0.29 g) were divided into 4 groups (4 replicates) each and were placed in 16 hapa nets (15 fish/hapa), mounted in an 800 m2 earthen pond. Fish were fed twice per day at 5% of the body weight. Sampling of the fish was done biweekly; mortalities were recorded daily while the physico-chemical parameters were monitored weekly. The growth performance and survival rates of the Nile tilapia were not significantly different (p > 0.05) between treatments. In conclusion, the present study indicates that full fat BSFLM can replace up to 100% of the FM without negative effects on the growth performance and survival rates of Nile tilapia, although the slight trend towards reduced growth for the 100% substitution diet points at the need for future studies on increasing the nutritional value of BSFLM, for example, by further processing.

Growth performance of tambaqui (Colossoma macropomum) supplemented with honey prebiotic in stagnant peat ponds

This study aims to evaluate the effectiveness of giving honey as a prebiotic in increasing the growth performance of freshwater pomfret (Colossoma macropomum). In this study, honey was mixed into the feed with the method coated at doses of 0.0%, 0.3%, 0.6%, and 0.9%. Fish with an initial body weight of 3-5 g are reared in three ponds with a total of 12 hapa nets measuring 1x1x1 (m3) (40 fish / hapa nets), that is, 4 hapa nets are placed in each pond. Thus, each treatment replication could be represented in each pond. Fish were fed treated with three replications for 60 days. The best growth performance during 60 days of maintenance indicated that honey supplementation with a dose of 0.6% was significantly different from other treatments in terms of the amount of feed intake 1195±0.01 g, FCR 1.12±0.00, feed efficiency 90.34±0.00 %, the daily growth rate was 3.88±0.02 %, and the body weight gain rate was 778.53±0.01 %. It can be concluded that the administration of honey with a dose of 0.6% is effective in improving the feed conversion ratio, increasing feed efficiency, daily growth rate, body weight gain, and reducing the amount of feed consumption of freshwater pomfret in inundated peat fish ponds.

Is culture performance of juvenile sandfish, Holothuria scabra, in ocean-based nursery systems influenced by proximity to milkfish (Chanos chanos) farms and hapa net mesh size?

The impacts of proximity to milkfish farms (i.e. ‘close’, ‘intermediate’ and ‘distant’) and different hapa net mesh sizes (i.e. 400 μm and 1 mm) on periphyton characteristics and growth performance of sandfish, Holothuria scabra, juveniles (4.6 ± 0.1 mm), were evaluated in a 30-day field experiment in the Guiguiwanen Channel at Bolinao, North-western Philippines. Growth and survival of sandfish juveniles were determined twice, and chlorophyll a and ash-free dry weight (AFDW) of periphyton were monitored every 5 days during the study. Opisthobranchs that recruited inside the hapa nets were identified and counted during monitoring. Survival of sandfish juveniles differed significantly between sites but was not influenced by mesh size by day 15. Survival was significantly higher at the intermediate site by day 15. Juvenile survival was significantly higher in 400 μm mesh hapa nets across all sites by day 30. Result showed that mean length and absolute growth rates (AGR) of sandfish juveniles were significantly influenced by mesh size but not by site at day 15. Juveniles reared in the 1 mm mesh hapa nets were larger and grew faster by day 15. However, by day 30, mean length and AGR of sandfish juveniles were significantly affected by site but not mesh size. Juveniles reared at the close site were significantly larger and grew faster than those reared at the intermediate site while mean length and AGR of juveniles reared at the distant site were not significantly different to those cultured at either the close or intermediate sites. Growth rates of juveniles were lower on day 30 compared to day 15 possibly resulting from reduced food availability, as indicated by lower periphyton AFDW, resulting from inter- and intraspecific competition. A positive correlation was found between AGR and the number of surviving sandfish juveniles by day 15, while no correlation between the two parameters was observed by day 30 indicating that reduced growth rates were not mediated by interspecific stocking density, but most likely resulted from high intraspecific grazing pressure. Chlorophyll a content of periphyton was higher during the second half of the experiment; however, total periphyton biomass (as AFDW) generally decreased overtime. This reduced food availability coincided with the higher number of opisthobranchs in the hapa nets by day 30. Results showed that sandfish juveniles can grow in an environment with varying levels of nutrient enrichment, however, areas close to mariculture activity may support improved growth because of resulting increases in periphyton biomass. Additionally, the use of finer mesh (400 μm) hapa nets positively impacted juvenile survival and would support earlier transfer of juveniles from the hatchery to the ocean reducing husbandry inputs and costs.

Nursery culture of sandfish Holothuria scabra in sea-based floating hapa nets: Effects of initial stocking density, size grading and net replacement frequency

Sea-based culture of early juvenile sandfish Holothuria scabra up to fingerling size (>2 g) using floating hapa nets has been confirmed as a viable nursery system in tropical countries such as the Philippines. However, production can be further optimized through more efficient rearing practices. In this study, we demonstrate the effects of initial stocking density, size grading and net replacement frequency during the culture of early juvenile sandfish in sea-based floating hapa nets (2 × 1 × 1 m). Testing different initial stocking density treatments ranging from 150 to 2000 early juveniles (4–10 mm; 0.02–0.06 g) per hapa net, we confirmed significantly faster growth (0.06–0.08 g d−1) and higher survival (72–97%) in low densities (≤500 hapa−1), compared to high densities (≥700 hapa−1: 0.02–0.04 g d−1; 67–80%). Low density culture can produce 2 g sandfish in about a month, while higher densities will require a 2–3 mo culture period to reach this size. Culture performance following size grading was also compared using three initial size classes (small, 0.05–0.99 g; medium, 1–1.99 g; and large, 2–3 g) and a mixed group (0.05–3.00 g). At 45 d, juveniles in pooled size-graded groups grew significantly faster (0.11–0.13 g d−1) than those in the mixed group (0.01 g d−1). Survival was significantly higher in the medium (85.3%) and large (84.7%) groups, than those in the small (54.4%) and mixed (45.6%) groups. However, size variation was not significantly mitigated by grading during the 45-d culture. Culture performance of sandfish was not significantly enhanced by more frequent net replacement for short-term rearing (30–45 d). Optimal results were gained from an initial stocking density of ≤500 early juveniles (5–10 mm) per floating hapa net which may be cultured in a month, without requiring net replacement and size grading to produce ≥2 g sandfish. However, in cases of high hatchery production, it is also feasible to adopt higher density stocking (e.g. >1000 hapa−1), but will require longer culture duration (60–85 d), monthly net replacement and size-grading to attain the same size. Results of this study can help fine-tune management practices for nursery culture of sandfish in sea-based floating hapa net nurseries in order to boost production of fingerlings needed for aquaculture and restocking.

Effects of feeding frequency on specific growth of tilapia (Oreochromis niloticus) fingerlings in hapa nets in fish ponds at in Kenya

Effects of feeding frequency on specific growth of tilapia (Oreochromis niloticus) fingerlings in hapa nets in fish ponds at in Kenya

Viability of a bottom-set tray ocean nursery system for Holothuria scabra Jaeger 1833

Scaling up the hatchery production of juvenile sandfish Holothuria scabra is constrained by limited hatchery space and the associated high operational costs. To shorten the hatchery rearing phase, ocean nursery systems like floating hapa nets have been used with good prospects but with limitations during rough sea conditions. In this study, the potential of bottom-set trays (0.14 m2) as an alternative ocean nursery system for early sandfish juveniles (0.5 ± 0.1 cm) was evaluated. The effects of stocking density and presence of artificial substrates (AS) on the growth and survival were determined in a 60-day field experiment. Average length and growth rates at lower stocking density treatment (100 individuals tray−1) were significantly higher (1.45 ± 0.22 cm; 0.03 ± 0.01 cm day−1) than at higher stocking density treatments (400 and 500 individuals tray−1) 0.95 ± 0.06 cm; 0.03 ± 0.004 cm day−1) with or without AS (p < .05) respectively. The coefficient of variation in length (CV) at high stocking densities were significantly higher than at low densities (p < .05) and growth rate was strongly negatively correlated with density. Survival was significantly higher (55% ± 9%) in trays with AS across all stocking density treatments than in trays without AS (34% ± 2%). Results suggest that AS may have reduced intra- and interspecific interactions, resulting to significantly lower growth variations and higher survival. The bottom-set tray with AS can be a practical alternative ocean nursery unit for rearing early sandfish juveniles particularly when the sea surface condition is rough. With improved design and density management, survival and growth may be further enhanced.

Net mesh size affects production of giant freshwater prawn Macrobrachium rosenbergii cultured in lake-based cages

Summary Cage culture of freshwater prawns in open waters is prone to the entry of predators and competitors that particularly hamper production. This study was conducted to determine how smaller net mesh sizes to reduce entry of unwanted species inside the cages affects the production of Macrobrachium rosenbergii in lake-based cages. Juvenile prawns were stocked in cages (7 × 7 × 1.5 m) of two net mesh sizes at 10 individuals m−2 and cultured for 10 months in a shallow eutrophic lake in the Philippines. The two net mesh sizes were either 5 mm-mesh B-nets or and 1 mm-mesh Hapa nets. Each treatment had four replicates each and was fed based on biomass with commercially formulated feed. Monitoring of various production parameters was done during the two phases of culture: batch phase on days 63 and 127 and the selective harvest phase on days 187, 219, 253, 281 and 313, when the experiment was terminated. For the first 127 days of culture, the weight, percent weight increase, daily growth rate (DGR), specific growth rate (SGR), yield and feed conversion ratio (FCR) were significantly better in prawns reared in the Hapa compared to the B-nets. During the selective harvest phase the blue claw, orange claw and berried females were selectively harvested and the remaining prawns returned to the cages. After changes in stocking density through culling, ancova was used to compare the effect of mesh size with the total number of prawns returned to the cages as a covariate. Yield was significantly higher in the Hapa nets. Weight, DGR, SGR and FCR were also consistently higher in the Hapa nets, although not always significantly different. The overall better performance of prawns reared in the Hapa net cages was due to: (i) the reduction in the entry of predator and competitor species in the finer-meshed Hapa compared to the larger mesh B-net, (ii) more natural food trapped inside the Hapa cages, and (iii) a higher number of selectively harvested prawns, which decreased stocking density in the cages and improved growth. Use of small mesh size nets is recommended in the cage culture of M. rosenbergii in inland natural water bodies.

Potentials of Kunnu Waste as Dietary Supplement for African Catfish Fingerlings

A 72 days feeding trial was conducted on African catfish (Clarias gariepinus) fed on five diets (CP 5 40%) in which maize was replaced with kunnu waste at 0%, 25%, 50%, 75% and 100% respectively. Fingerlings of C. gariepinus were assigned to the five diets in a completely randomized design at 36 fish per treatment in Hapa nets suspended in an outdoor concrete tank; experimental fish were fed at 5% biomass daily. Results on performance and feed utilization showed linear correlation between specific growth rate and body weight gain (p . 0.05). However, feed intake increased with increased dietary levels of kunnu waste (p , 0.05). The best feed conversion ratio (FCR) was obtained from the control group while the poorest was recorded at 100% replacement (p . 0.05). This finding indicated that C. gariepinus can tolerate kunnu waste as dietary replacement for maize without adverse effect on performance.

Performance of catfish (Clarias gariepinus, Burchell, 1822) fed enzyme supplemented dried rumen digesta

The growth response of catfish (Clarias gariepinus) fingerlings fed with varying levels of enzyme supplemented dried rumen digesta meal (EDRD) was conducted for 70 days in Nursery cages (hapa nets) suspended in outdoor concrete tanks. One hundred and fifty (150) fish were randomly assigned to five diets formulated such that EDRD replaces soybean at 0, 10, 20, 30, and 40%, respectively. Thirty fish were assigned to each of the diets in hapa nets and fed at 5% body weight daily. Evaluation of growth parameters and nutrient utilization of fish followed standard methods and were based on feed intake, weight gain, feed conversion ratio, specific growth rate and protein efficiency ratio. Result showed that control (0%) diet gave highest weight gain of 54.25 g followed by 10, 20, 30%, while the least weight gain was obtained from 40% dietary treatment which recorded a value of 36.09 g. This experiment revealed that EDRD can be tolerated by C. gariepinus fingerlings and support growth at 40% with little effect on specific growth rate (SGR) and feed conversion ratio (FCR) (p<0.05). There was no mortality encountered during the experimental period. Key words: Catfish (Clarias gariepinus), enzyme supplemented dried rumen digesta meal (EDRD), fish, shellfish.

Growth Response of African Catfish (Clarias gariepinus, Burchell 1822) to Dried Rumen Digesta as a Dietary Supplement

2 Abstract: The growth response of catfish (Clarias gariepinus) juveniles fed Dried Rumen Digesta (DRD) based diets was investigated for 9 weeks in hapa nets. One hundred and eighty (180) fish were randomly assigned to five diets formulated such that DRD replaced groundnut cake at 0, 10, 20, 30 and 40% represented as diets A, B, C, D and E respectively. Thirty six fish were assigned to each of the diets in hapa nets and fed at 5% body weight daily. Results showed that control diet 'A' gave the highest weight gain followed by 'B' and 'C' but poor results were obtained from diets 'D' and 'E'. There were significant differences (p 0.05) of fish fed diets 'A' and 'B' but were significantly different (p<0.05) from diets 'C', 'D' and 'E'. This experiment revealed that DRD can be tolerated by Clarias gariepinus juveniles and support growth when dietary inclusion does not exceed 20%.