Over the past several years, Indonesian freshwater aquaculture has intensified, with a concomitant increase in the use of commercial pellets. To assess the effects of pond aquaculture intensification on nutrient dynamics, we monitored nutrients and fish production in a small-scale fish farm in West Java province. The studied system consisted of semiintensive giant gourami (Osphronemus goramy) production in four small earthen ponds (353-482 m 2 each and 0.46-0.55 m deep). Nitrogen (N) and phosphorus (P) fluxes through the ponds were monitored, and data on fish production and nutrient accumulation in sediments were collected during a 5-month production cycle. Results showed that, on average, 61% total N and 77% P inputs were trapped in the accumulated sediments. Only 15% of total N and less than 3% P inputs introduced into ponds were recovered in harvested fish. Sediment nutrient accumulation increased linearly with total nutrient input. The consequences of intensification of giant gourami aquaculture using this production model are explored in terms of nutrient use efficiency and environmental impact.

The NWAC103 strain is an improved channel catfish Ictalurus punctatus that has been widely used in the catfish industry. However, it is not yet known whether the hybrid progeny (hereafter termed 103 hybrids) of male blue catfish I. furcatus and NWAC103 females will exhibit further improvement in growth. Therefore, we compared production attributes among four catfish genotypes that were communally reared in earthen ponds: NWAC103, Kansas Select 21 channel catfish, Rio Grande × D&B‐strain blue catfish, and 103 hybrids. Compared with the other genotypes, the 103 hybrids had a higher (P < 0.05) growth rate during the food fish stage, better survival when exposed to natural epizootics of enteric septicemia of catfish, and greater production and survival when exposed to critically low levels of dissolved oxygen. Mean weights at the food fish stage were 639.0 g for 103 hybrids, 569.7 g for NWAC103, 514.7 g for Kansas Select 21, and 394.3 g for blue catfish. Production rates were 8,632 kg/ha for 103 hybrids, 5,205 kg/ha for NWAC103, 6,250 kg/ha for Kansas Select 21, and 4,582 kg/ha for blue catfish. Fingerling survival rates were 100% for 103 hybrids, 25.7% for NWAC103, 43.5% for Kansas Select 21, and 72.9% for blue catfish; food fish survival rates were 88.7, 60.0, 82.7, and 76.3%, respectively. The heterosis for body weight was only 12.2%, but the combination of faster growth and greater survival resulted in 65.8% heterosis for production. Channel catfish that have been genetically improved through selection programs can be used to produce channel × blue catfish hybrids with higher performance than the parental species. The improvement via selection does not limit further enhancement via hybridization.

Here, on the basis of published information upon over 800 species from 39 orders and 202 families, we analyse how the size of oil globules in fish eggs varies between reproductive guilds and environments with contrasting salinities. About 80% of marine fishes produce eggs with oil globules, the volume of which (VO) never exceeds 9% of the egg reserves and averages 2%. These proportions vary very little between marine fish species producing pelagic or demersal eggs. Fewer freshwater fishes (about 40%) produce eggs with oil globules, but their globules are much larger (mean VO of 10%) and their volumes vary considerably between reproductive guilds: VO is on average 3–10 times lower in freshwater species with demersal eggs than among freshwater pelagophils and aphrophils (i.e., bubble nesters), where it averages about 40% (range of 23%–69%) of the egg reserves. These results support the idea that oil globules serve to hydrostatic lift in fresh waters, but not or very little in marine waters, where egg buoyancy can be achieved at a lower energy cost through egg hydration. Advantages and constraints of oil globules in fish eggs are discussed in the light of species producing eggs with very large oil globules (VO > 20%): access to oxygen‐rich water layers that are indispensable for egg development vs. smaller size of larvae at first feeding, since the saturated lipids contained in oil globules essentially serve very little to tissue construction.

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This study addresses rapid methods to identify mature channel catfish, Ictalurus punctatus, females for induced spawning with luteinizing hormone releasing hormone analog (LHRHa) and common carp pituitary extract (CPE) and the effects of stage of maturity, hormone dose, season, and cannulation before hormone injection. Hormonal intervention is the most effective method for inducing maturation and spawning in channel catfish × blue catfish, Ictalurus furcatus, hybrids. A total of 80 mature channel catfish were staged for maturity based on secondary sexual characteristics and 20-30 oocytes cannulated to ascertain their maturation stage based on the position of gonadal vesicle. Twenty females were randomly assigned to one of the four hormone regimes (priming + resolving dose): CPE 2 + 8 mg/kg (CPEC); LHRHa 20 + 40 μg/kg (LHRHaL); LHRHa 20 + 60 μg/kg (LHRHaM); and LHRHa 20 + 80 μg/kg (LHRHaH) and a fifth treatment consisted of 20 females selected based on apparent maturity as evidenced by external appearance were injected with CPE, 2 + 8 mg/kg without cannulation (CPEO). Two trials were conducted in early part of the spawning season and two trials in peak season. External methods to identify maturity correlated (r = 0.63) with that of "germinal vesicle position" method to identify the stage of maturity in females. Mean percent of females that ovulated, hatched, and fry produced per kg body weight did not differ (P > 0.05) among the five hormone treatments. The mean percent females that ovulated was higher (P < 0.05) for CPE-induced females that were identified as "excellent" females based on external examination. The performance of cannulated females did not differ (P > 0.05) with that of noncannulated catfish. The mean egg quality of hormone-induced females and percent of females ovulated in response to hormone treatment established a weak but significant linear relationship (Y = 3.85 + 0.008 × ovulation, r 2 = 0.39, P < 0.05).