ALBERT

Notes: 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−1 compared with 1.1–1.6 g per fish day−1 for younger fish (3). The comparable ranges for mrigal were 1.9–2.8 and 1.4–2.1 g per fish day−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=−1.421+1.716X, where Y is the daily weight gain of Nile tilapia and X is the fertilizer level, r2=0.98, P〈0.01, n=12). At a high level of fertilization (3.0 kg N:1.5 kg P ha−1 day−1), performance of stunted fingerlings (5 and 12) of both rohu and mrigal was similar (range 2.3–2.8 g per fish day−1, P〉0.05), but younger mrigal (M3) grew faster than rohu (2.1 g per fish day−1 and 1.6 g per fish day−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−1 day−1), suggesting the impact of age of seed on competition within polycultures. The net fish yield (NFY) of tilapia was not affected significantly (P〉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−1 day−1) was calculated at 4.06±0.08 g·m−2 day−1, which was significantly higher (P〈0.001) than the yield (1.82±0.12 g·m−2 day−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.

Notes: Cycles of movement and feeding of African catfish, Clarias gariepinus (Burchell 1822) fingerlings (113.48 ± 1.87 mm total length) were studied using an infrared illumination and video recording system. The study was carried out over a 15-day period with a group of 40 fish held at 30 °C under a 12-h light:12-h dark photoperiod. The fish were nocturnal and took over 70% of their daily ration at night when given access to food 24 h a day. When feeding was restricted to the light phase, feeding activity decreased, but nocturnal feeding was restored from the second day after a return to 24-h food access.

Notes: An 8-week feeding trial was conducted using tilapia, Oreochromis niloticus L., in a recirculation system maintained at 27±0.2°C to observe the negative effects of Sesbania endosperm on growth and nutrient utilization. Five experimental diets were formulated to contain 32% protein, of which fishmeal was the major source. Endosperm separated from Sesbania seeds was included at levels of 0.0%, 2.9%, 5.8%, 8.7% and 11.6% in diets 1 (control), 2, 3, 4 and 5, respectively, equivalent to levels of 0.0%, 9.7%, 19.4%, 29.1% and 38.8%, respectively, of whole Sesbania seeds. Each treatment had two replicates, eight fish per replicate, with a mean initial live weight of 5.2±0.1 g. Fish were fed 20 g per  kg metabolic body weight of fish daily. The body weight gain, metabolic growth rate, feed conversion ratio, protein efficiency ratio, protein productive value and energy retention of fish fed the control and diet 2 were significantly better (P〈0.05) than those of fish fed the other diets. Physical observation showed that the intestines of the fish fed diets that included endosperm contained loose, viscous and sticky material. Fish fed diets 3, 4 and 5 had a lower proportion of dry matter in their faeces, and lower apparent crude lipid and energy digestibility coefficients compared with fish fed the control diet and diet 2. They also had significantly reduced levels of muscle and plasma cholesterol, whole-body crude protein, lipid and gross energy.

Notes: An 8-week feeding trial was conducted in a warmwater recirculation system at 27 ± 0.2 °C to evaluate the nutritive value of dhaincha (Sesbania aculeata) seed meal as a possible fish meal substitute in the diet of tilapia. Five isonitrogenous and isoenergetic diets were formulated to contain 32% crude protein and 18.4 kJ g−1 gross energy. Sesbania seed meal was included in diets at various levels [0%, 9.7%, 19.4%, 29.1% and 38.8% for diets 1 (control), 2, 3, 4 and 5, respectively, which correspond to 0%, 10%, 20%, 30% and 40% of dietary crude protein]. Each treatment had two replicates, eight fish per replicate, with mean initial weight of 7.06 ± 0.03 g. Fish were fed 20 g kg−1 metabolic body weight daily. On the basis of the observed growth rate, feed conversion ratio, protein efficiency ratio, apparent net protein utilization and energy retention, diets 1 (control) and 2 (containing 9.7% Sesbania meal) were similar and significantly (P 〈 0.05) better than the other dietary groups. Fish fed diets 3, 4 and 5 containing higher levels of Sesbania meal showed significantly reduced growth performance compared with those fed diets 1 and 2. Fish fed diets 3, 4 and 5 had significantly lower faecal dry matter (DM) content, apparent crude protein, lipid and energy digestibility and reduced levels of cholesterol compared with the control and diet 2. Fish fed diets containing higher levels (〉9.7%) of Sesbania meal had significantly higher whole-body moisture, lower lipid and gross energy content. The lower growth performance of fish fed diets containing higher levels of Sesbania meal is thought to result from the presence of tannins, saponin and the non-starch polysaccharide content of the seed. The results of this study showed that inclusion of up to 9.7% untreated Sesbania seed meal (10% of the dietary protein) in the diet did not affect the growth performance and nutrient utilization in tilapia.

Notes: Morphological changes are described in Japanese flounder Paralichthys olivaceus larvae and juveniles with emphasis on growth during the period of metamorphosis. Ontogenetic changes in condition factor and lipid, glycogen and protein levels were also analysed to determine the utilization of stored energy. Fish grew from 6·6 to 20·3 mm LT(1·15 to 84·4 mg in mass, M) during the period from 11 to 40 days after hatching (DAH) at 19·3° C. Per cent specific growth rate per day (%G day−1) for wet mass was lowest during the metamorphic phase (21–30 DAH) compared to pre-(11–20 DAH) and post-metamorphic (31–40 DAH) phases. When LT and M were expressed as 〈inlineGraphic alt="inline image" href="urn:x-wiley:00221112:JFB251:JFB_251_mu1" location="equation/JFB_251_mu1.gif"/〉, the b value was highest during the pre-metamorphic phase and lowest during the metamorphic phase. These findings indicate that the developmental changes that occur during metamorphosis of Japanese flounder are closely related to the growth pattern. Moisture, lipid and glycogen contents were also at the lowest level during metamorphosis compared to pre- and post-metamorphosis, which suggest that Japanese flounder use their energy reserves to accomplish metamorphosis due to an apparent decline in feeding during this period.