Hapa Nets Research Articles

The growth and gonadal maturation of the African catfish, Clarias gariepinus (Burchell) broodstock fed differently heated soybean-based diets

An investigation was carried out to assess the growth and gonadal maturation of Clarias gariepinus (Burchell) fed differently heated soybean diets in concrete tanks. Four hundred and eighty male and female C. gariepinus (182 ± 10 g for females and 208 ± 5 g for males) were randomly distributed in groups into hapa nets. Iso-nitrogenous (310 g kg⁻¹ crude protein) and iso-caloric diets (355 Kcal kg⁻¹) prepared from raw soybean (D0) and soybean autoclaved for 5, 10, 15, 20, 25 and 30 min labelled D0, D5, D10, D15, D20, D25 and D30, were fed to the fish for 84 days. The fish meal based diet tagged DFM served as control. The male and female broodfish fed the fish-meal-based diet and diet D25 had significantly higher (P < 0.05) growth performance, gonad maturation, gonadosomatic index, relative fecundity and percentage egg fertilization and hatchability than the fish fed the other diets. The females had significantly higher (P < 0.05) weight increases and healthier condition over their male counterparts fed the same diets. This study showed that diet D25 was found to be the best substitute for fish meal that provided adequate nutrients required for the formation of genital products that produced strong offspring in C. gariepinus broodstock culture.

Características morfométricas, rendimento e composição do filé de tilápia do Nilo, Oreochromis niloticus, da linhagem tailandesa, local e do cruzamento de ambas

Morphometrics, fillet yield and fillet composition differences were researched in Nile tilapia, Oreochromis niloticus, strain thai-chitralada (Tai), Brazil (Local) Northern Paraná and their hybrid (Hbr, male Thailand x Brazilians female ). The experiment was designed entirely randomly with three treatments (strains) and three repetitions per treatment in hapa nets in ponds. The initial weights were 0.39 ± 0.20, 0.45 ± 0.22 and 0.41 ± 0.15 g for the strains Tai, Bras and Hbr, respectively. At the end of the experiment, the weights were 650.67, 534.25 and 360.00 g for the same previous sequence, with statistically significant differences between groups (P < 0.05). Four morphometric proportions were established to characterise each group. For the ratio (head height)/(head length), the Tai strain was largest (P < 0.05) as compared to the two other strains. The other morphometric proportions were not different (P > 0.05). The strain Hbr produced (P < 0.05) greater fillet yield (39.05%) when compared to Local (38.00 %) and Tai (36.51 %), the latter two were not different from each other (P > 0.05). Considering fillet composition, Local strain had the least crude lipid content of (1.88 %), as compared to Hbr (2.44 %) and Tai (2.96 %) which were significantly different (P 0.05).

A test of an on-farm selection procedure for tilapia growth in Indonesia

Modern intensive fish farming encourages the use of superior strains of fish developed in centralized research institutions. In many artisanal fish farms these strains may not be available or suitable: environmental conditions may differ from those optimal for the superior strains, or the species of fish desired in particular farming systems may not have been the subject of a selection programme. In such cases, the option would be for farmers to improve their own strains using procedures that are within their financial and technical capabilities. One generation of mass selection for size-specific growth rate of tilapia was performed on a fish farm in West Java, Indonesia. Selection was applied in two steps over the 6 month grow out period following the initial stocking of size-graded fingerlings acquired from the farmer. Size grading, rather than age-matching, was a key step in simplifying the procedure for on-farm use. Selection and testing of the offspring were conducted in hapa nets set up in farm ponds. The selection resulted in a significant positive response of 2.3% as measured by the percent differences of the lengths of the selected offspring from the control offspring. A rough estimate of realized heritability amounted to 0.12.

Nursery rearing of Penaeus monodon (Fabricius) using suspended (hapa) net enclosures installed in a pond

The use of suspended (hapa) nets as nursery enclosures for shrimp fry was tested. In the first trial, four stocking densities (72, 144, 288, and 432 fry m −3) of P. monodon fry (PL 20, body weight = 8 mg, body length = 12.6 mm) were evaluated in 1×1×1.5 m hapa nets. Results showed that shrimp BW, BL, and survival rates were inversely related to stocking density. Shrimp fry stocked at 72 fry m −3 attained significantly greater BL of 22 and 37 mm and BW of 50 and 260 mg after 15 and 30 days, respectively, and survival of 92%. A verification trial using PL 28 (BW = 10 mg, BL = 13.2 mm) at a stocking density of 288 fry m −3 in hapa nets of 2×3×1.5 m yielded a mean survival of 97%, BL 48.1 mm, and BW 780 mg. Hapa nets are therefore useful as alternative shrimp fry nursery systems in the absence of specialized tanks or pond nursery facilities.

Hatchery production of Oreochromis niloticus L. at different sex ratios and stocking densities

The influence of various sex ratios and stocking densities on hatchery production of Nile tilapia, Oreochromis niloticus L., was studied in land-based (concrete tanks) and lake-based (hapa nets) systems. In both hatchery systems, egg and fry production was maximum at a sex ratio of 4:1 females to males and a density of 4 females per m 2. Seed production varied significantly among treatments at different periods of the year. In concrete tanks, significantly high seed production of 12.98 and 11.77 eggs and fry per spawner per day was obtained in March and August, respectively. In hapa nets, irrespective of sex ratios, 10.18 seeds per spawner were collected daily in March. In relation to the broodstock density in concrete tanks, significantly bigger daily harvests of 13.41 and 13.00 eggs and fry per spawner were produced in late February and March, respectively. In hapa nets, daily harvests of 8.95 and 7.74 eggs and fry per spawner were the highest seed production levels which occurred in April and March, respectively. Seed production was significantly higher in concrete tanks than in hapa nets while insignificant differences ( P>0.05) were found among sex ratio and broodstock density treatments.