Potential role of L-ascorbic acid with Field cricket (Gryllus bimaculatus) meal in diets of Nile Tilapia (Oreochromis niloticus) during sex reversal and nursing

A synthetic androgen 17-α methyltestosterone (MT) commonly used in the production of mono-sex fry of Nile tilapia (Oreochromis niloticus) during the first 21 days for sex reversal has been considered to suppress immunity thereby reduce survival. Present trial was conducted to evaluate whether vitamin C (L-ascorbic acid, AA) supplementation would benefit in terms of survival, growth, and stress resistance. Nile tilapia fry were fed with isonitrogenous (57.8±0.2% CP) diets formulated using Field cricket (Gryllus bimaculatus) meal (approx. 79%) and fish meal (approx. 20%) to use as control, and five other diets were prepared by supplementing 10, 20, 30 40 and 50 g of vitamin C (L-ascorbic acid per kg diet). Eighteen aquaria or glass tanks (100 L) were used having three replicates per treatment. Each aquarium was stocked with 300 fish (0.01±0.00 g). Fry were nursed for another 91 days to check their sex-ratio. Gonad histology showed increased number of spermatogonia when L-ascorbic dose was 30g/kg diet. At the end of the feeding trial results indicated significant increase (P<0.05) in growth, feed utilization and survival when fed with vitamin C at the dose of 10 g/kg diet during sex-reversal and nursing periods as compared to the control. Similarly, hematological information also showed 10 g vitamin C dose per kg diet. Polynomial regression showed that the optimum dietary ascorbic acid doses were calculated at 15.9, 10.0 and 12.0 g AA per kg diet for highest survival (83.5% max), weight gain and SGR, respectively, but the doses higher than 20 g of L-ascorbic acid/kg diet was not beneficial. Highest apparent digestibility (AD%) of protein (84.1%) was at 15.37g and AD% of lipid (91.4% max) was 17.8g of vitamin C/kg diet. Salinity challenge test also showed highest survival can be achieved at 15.8 g AA per kg diet. As the survival of fry is the most important parameter at these stages, the dose which resulted highest survival i.e., 15 g/kg diet is recommended

Optimization of Phosphorus Fertilizer in Supplemental Feed‐Fed Based Nile Tilapia (Oreochromis niloticus) Ponds

An experiment was conducted in earthen ponds at the Asian Institute of Technology, Thailand to determine different phosphorus fertilizer dose effects on Nile tilapia production, water quality variables, nutrient utilization and cost‐benefit under supplemental feeding. Five phosphorus fertilization rates were used as treatments e.g. 100%, 75%, 50%, 25% and 0% of 7 kg P ha week−1. Nitrogen fertilization rate was fixed at 28 kg N ha week−1 for all the treatments. Sex‐reversed Nile tilapia were stocked at 3 fish m−2, and 30% CP floating feed fed at 50% satiation feeding rate. Nutrient budget showed higher phosphorus fertilizer input resulted in higher phosphorus sink in the sediment. Mean weight, mean weight gain, daily weight gain and net yield were not significantly different among treatments (P > 0.05). Total Kjeldahl nitrogen, total phosphorus and soluble reactive phosphorus were significantly different among treatments. Economic analysis showed phosphorus fertilization resulted in positive net returns. Though the gross income was not affected by different fertilization rates, significantly lowest cost was found in the treatment using 25% phosphorus fertilizer. It can be concluded from the research that 25% phosphorus fertilization might be used as an alternative strategy of Nile tilapia pond culture in terms of economic return and nutrient loss in sediment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115936/1/are12444.pd

Reproductive performance and the growth of pre-stunted and normal Nile tilapia (Oreochromis niloticus) broodfish at varying feeding rates

A 119-day experiment was conducted to investigate the effects of feeding rate and reproductive performance of stunted (S) and non-stunted or normal (N) Nile tilapia (Oreochromis niloticus). Both the groups were reared in tanks re-circulated with bio-filtered water and fed with floating pellets (30% crude protein) twice daily. Seed were harvested weekly from the mouths of incubating females. The study showed that early stunting with subsequent high feeding rate can improve both growth and reproductive output in female Nile tilapia. Broodfish type and feeding rate showed significant (P less than 0.05) effects on both the frequency of spawning and the seed output. In general, seed output from normal broodfish increased linearly over the experimental period at all the feeding rates. However, seed output from stunted broodfish showed a linear increment for 3% feeding rate, exponential increment for 2% but quadratic for 1% showing decline after 10th week of the trial period. Results also showed that trends of seed output from stunted broodfish increased linearly with the increase in feeding rate showing that optimum rate could be higher than 3%. While from normal group the relationship was quadratic; increasing from 1%, peaked at 2% and declined at 3% feeding rate. Final GSI of the stunted females was significantly (P less than 0.05) higher than that of normal females. The GSI of stunted fish showed a decreasing trend with the increased feeding rate. Both the broodstock groups fed at 1% biomass grew linearly whereas at 2 and 3%, they grew exponentially. As compared to the normal, stunted broodfish had significantly (P less than 0.05) higher fat content in viscera although similar levels were in carcass and ovary. Carcass fat content was significantly (P less than 0.05) lower in fish fed at 1% biomass but significantly (P less than 0.05) higher in the ovary and viscera of fish fed at 3% biomass. This study shows that tilapia hatchery operators could manipulate the seed production according to the seasonal demand by using appropriate broodstock stunting and feeding strategies

Advanced nursing of mixed-sex and mono-sex tilapia (Oreochromis niloticus) fry, and its impact on subsequent growth in fertilized ponds

A 168-day grow-out trial was conducted using mono-sex and mixed-sex tilapia (Oreochromis niloticus) fries nursed for 2, 4 or 6 months to investigate the comparative effects of advanced nursing on subsequent growth and survival. Fingerlings were kept in nylon hapas and fed at 5% biomass day&minus;1 during advanced nursing (4 or 6 months) before stocking at 3 fishes m&minus;2 in 18 fertilized earthen ponds (200 m2). Survival rates of mono-sex and mixed-sex tilapia during advanced nursing were comparable (greater than 70%). During the subsequent grow-out phase, survival of both mono-sex and mixed-sex tilapia increased linearly with duration of nursing (y=36.12+4.93x, n=9, r2=0.56, P less than 0.05 and y=21.38+8.45x, n=9, P less than 0.05), respectively. Prolonged nursing increased the level and consistency of survival in both mixed- and mono-sex stocks during subsequent grow-out. Overall, mono-sex fishes reached a larger final individual size (128.8&plusmn;6.8 g) than mixed-sex (112.7&plusmn;14.6, P less than 0.05). This effect was most pronounced for the 6-month-old seed of which mixed-sex reproduced early in the production cycle. However, survival, daily weight gain, specific growth rate and net fish yield were not significantly different (P greater than 0.05) between mono-sex and mixed-sex tilapia. A decreasing trend in daily weight gain, specific growth rate and individual harvested size of the stocked fishes was observed with increase in nursing period in mixed-sex tilapia due to reproduction. It was concluded that the duration of nursing was critical to producing homogeneous mixed-sex fish, and that prolonged nursing may be a useful strategy for production of mono-sex tilapias

Nursing duration and pond fertilization level affect polycultures of Indian major carp (rohu Labeo rohita and mrigal Cirrhina mrigala) with monosex Nile tilapia Oreochromis niloticus

This study investigated the effects of nursing duration on the subsequent performance of rohu (R) Labeo rohita and mrigal (M) Cirrhina mrigala in polyculture with monosex male Nile tilapia (T) Oreochromis niloticus at four levels of pond fertilization. Nile tilapia, rohu and mrigal were stocked at a ratio of 4:1:1 in a 90-day trial based on 40 20-m2 pens fixed in four 400-m2 earthen ponds. Growth of carp fingerlings during prolonged nursing (5 or 12 months) was stunted compared with fish nursed over a conventional duration of 3 months (3) but showed superior growth subsequently. Mean daily weight gain of stunted rohu (12) ranged from 2.2 to 2.8 g per fish day&minus;1 compared with 1.1&ndash;1.6 g per fish day&minus;1 for younger fish (3). The comparable ranges for mrigal were 1.9&ndash;2.8 and 1.4&ndash;2.1 g per fish day&minus;1. Growth of Nile tilapia was inversely related to duration of carp nursing at the four levels of fertilization. Nile tilapia showed more response to increasing levels of fertilizer input (Y=&minus;1.421+1.716X, where Y is the daily weight gain of Nile tilapia and X is the fertilizer level, r2=0.98, P less than 0.01, n=12). At a high level of fertilization (3.0 kg N:1.5 kg P ha&minus;1 day&minus;1), performance of stunted fingerlings (5 and 12) of both rohu and mrigal was similar (range 2.3&ndash;2.8 g per fish day&minus;1, P greater than 0.05), but younger mrigal (M3) grew faster than rohu (2.1 g per fish day&minus;1 and 1.6 g per fish day&minus;1 respectively). Older rohu (12) appeared to perform particularly well, and Nile tilapia poorly at the lowest level of fertilization (1.5 N:0.75 kg P ha&minus;1 day&minus;1), suggesting the impact of age of seed on competition within polycultures. The net fish yield (NFY) of tilapia was not affected significantly (P greater than 0.05) by differential stocking age of carps; therefore, combined NFY of the three experimental fish species was not affected by the age of carp, as tilapia was the dominant species in polyculture. The highest combined NFY of all species in the most intensively fertilized pond (3.0 N:1.5 P kg ha&minus;1 day&minus;1) was calculated at 4.06&plusmn;0.08 g&middot;m&minus;2 day&minus;1, which was significantly higher (P less than 0.001) than the yield (1.82&plusmn;0.12 g&middot;m&minus;2 day&minus;1) from the pond with the lowest fertilization. At the highest fertilizer level, tilapia, rohu and mrigal contributed 72%, 14% and 14%, respectively, to the NFY, whereas the ratio was 60%, 20% and 20% at the lowest fertilization level. The study indicated that yields from tilapia in polyculture with the two carp species in more eutrophic water can be optimized if advanced nursing of carps is practised. Moreover, higher inputs of inorganic fertilizer and advanced nursing of carp are economically attractive under Bangladeshi conditions. Advanced nursing of rohu also improves its performance in more extensive systems when tilapia densities are high

Temporal variation of grouper diversity and distribution on the continental shelf of Sri Lanka: A revisit after four decades

Groupers (family Epinephelidae, subfamily Epinephelinae) are reef fishes of high value as food resources that generate export revenue to Sri Lanka. Yet, with less attention and poor resource management, grouper population dynamics remain understudied. This paper investigates the temporal variation of grouper species on the continental shelf of Sri Lanka in relation to seasonal, regional, and seafloor depth variables using data based on quantitative sampling of demersal fish conducted in 1978, 1979, 1980, and 2018 with a bottom trawl on the R/V Dr. Fridtjof Nansen, where the authors joined the 2018 survey. A total of 277 trawl samples were included in the analysis. The analysis of variance of all the grouper species found that the average density significantly declined from 0.89 t/NM2 (tonnes per square nautical mile) in 1979 to 0.28 t/NM2 in 2018. The contribution of groupers to the total catch (by weight) was also higher in 1979 (9.06 %) than in 2018 (1.28 %). The distribution patterns significantly differed among the six regions of the Sri Lankan shelf. In addition, seafloor depth was negatively correlated with grouper density. The results point to an urgent need for better management and conservation of the grouper resources

Selection of a commercial feed for Nile tilapia (Oreochromis niloticus) broodfish breeding in a hapa-in-pond system

A 95-day trial was conducted on a commercial farm in Thailand to compare the performance of three locally available feeds on the seed production of Nile tilapia (Oreochromis niloticus). Three hundred and sixty female Nile tilapia (mean weight&plusmn;SE, 91.5&plusmn;2.3 g) with the same numbers of male (123.4&plusmn;2.1 g) were stocked in each of 12 large nylon hapas suspended in two fertilized earthen ponds. An estimated 16 million eggs and yolk-sac fry were collected from the mouths of incubating females using hand nets at 5-day intervals. Broodfish were fed near to satiation twice daily. The female groups fed with large and small catfish pellets produced 27% and 30% more (P less than 0.05) seed, respectively, as compared to those females that were fed a herbivorous diet. Seed outputs from the catfish pellet-fed fish were 138&plusmn;6 and 141&plusmn;5 seed m&minus;2 day&minus;1, respectively, while that from herbivorous feed was 108&plusmn;2 seed m&minus;2 day&minus;1. Broodfish consumed the small catfish pellets more readily than the large catfish pellets and grew faster on this diet. These results showed that excess energy enhanced somatic growth rather than the reproductive output of the fish. The number of seed per gram of feed was significantly higher (P less than 0.05), which resulted in the lowest production cost when the females were fed with the large catfish pellets as compared to the females that received the smaller catfish pellets and the herbivorous feed. Overall seed yield and the clutches started to decline after the second month of the experimental period regardless of the type of feed given, showing quadratic relations. It indicated that an appropriate feed with a sound feeding strategy is required to minimize hapa fouling and maintain good water quality, and thereby produce high seed yield for longer periods

Productivity and constraints analysis of commercial tilapia farms in Ghana

This study examined the factors affecting productivity and constraints of commercial tilapia farms in the Dangme West District of the Greater Accra Region of Ghana. Primary data was obtained from 41 tilapia farms using multistage sampling. The data was then analyzed using descriptive statistics and regression analysis, and the agreements within ranked constraints was assessed. The empirical results revealed that the tilapia farmers in the three towns from which the data were collected, namely Achavanya, Kajanya and Dormeliam, produced a mean output of 74 kg per cage (6 m × 6 m × 3 m) as a productivity measure. Productivity of the cage farms were found to be positively affected by quantity of seed, feed and education level of managers; and negatively affected by cage size, labour and year of experience. Furthermore, the major constraints identified were high cost of inputs, lack of access to feed and credits and in adequate extension services and stealing of fish. The study suggests the need for supporting policies on inputs such as fingerlings and feed, and also providing education i.e. training to tilapia farmers. Efforts should also be made by financial institutions and NGOs to make credit easily available and accessible to commercial fish farmers so that they could cope with high cost of inputs

Effect of broodfish exchange strategy on the spawning performance and sex steroid hormone levels of Oreochromis niloticus broodfish in hapas

The productivity of Nile tilapia (Oreochromis niloticus L.) broodfish, spawned in large hapas (120 m2) in ponds under different exchange and management strategies, was monitored over a 70-day period. Female fish were checked for eggs twice weekly and returned to the same spawning hapa throughout the experiment (0 day) or exchanged for females maintained in separate single sex groups at high density for a period of 7 days at each (3.5 days) or alternate (7 days) harvests. Exchanged females were conditioned in separate hapas (20 m2) in the same pond. Production of eggs per unit area were significantly higher (P less than 0.05) in females exchanged weekly (7 days, 64 eggs m&minus;2 day&minus;1) or at each harvest (3.5 days; 55 eggs m&minus;2 day&minus;1) than for fish remaining in the spawning hapas throughout the trial (0 day, 33 eggs m&minus;2 day&minus;1). A greater proportion of conditioned females (3.5 days and 7 days) was spawned than in the control group (18% females compared to 11% per harvest). Conditioning of female broodfish had no effect on the egg clutch size (P greater than 0.05). Female productivity (eggs kg&minus;1 day&minus;1) was significantly lower for fish exchanged after every harvest (3.5 days) than those remaining in spawning hapas for alternate harvest (7 days) or throughout the experiment (0 day). Gonadal steroid (testosterone, T and oestradiol, 17&beta;-E2) and calcium levels sampled at the end of the experiment reflected spawning performance; serum T and E2 were highest in exchanged females. Non-spawned fish had elevated steroid levels compared to females incubating seed at harvest (e.g., 19.5&ndash;91.4 and 7.2&ndash;21.5 ng ml&minus;1 T for non-spawned and spawned fish, respectively). Stocking of the Indian Major carp Labeo rohita in spawning hapas to control fouling did not improve water quality and led to a significant depression of seed production (P less than 0.05). Regular exchange of female broodfish from spawning hapas with conditioned fish can improve productivity of hapa-in-pond system

Temporal variation of grouper diversity and distribution on the continental shelf of Sri Lanka: A revisit after four decades

Groupers (family Epinephelidae, subfamily Epinephelinae) are reef fishes of high value as food resources that generate export revenue to Sri Lanka. Yet, with less attention and poor resource management, grouper population dynamics remain understudied. This paper investigates the temporal variation of grouper species on the continental shelf of Sri Lanka in relation to seasonal, regional, and seafloor depth variables using data based on quantitative sampling of demersal fish conducted in 1978, 1979, 1980, and 2018 with a bottom trawl on the R/V Dr. Fridtjof Nansen, where the authors joined the 2018 survey. A total of 277 trawl samples were included in the analysis. The analysis of variance of all the grouper species found that the average density significantly declined from 0.89 t/NM2 (tonnes per square nautical mile) in 1979 to 0.28 t/NM2 in 2018. The contribution of groupers to the total catch (by weight) was also higher in 1979 (9.06 %) than in 2018 (1.28 %). The distribution patterns significantly differed among the six regions of the Sri Lankan shelf. In addition, seafloor depth was negatively correlated with grouper density. The results point to an urgent need for better management and conservation of the grouper resources