Desirable food characteristics

The cultivation of the larvae of Macrobrachium rosenbergii is performed under controlled hatchery conditions, which are quite distinct from grow-out techniques, including feeding strategies. The developing larvae are very small, extremely fragile and remain quite primitive during the early stages using partially developed systems (e.g. digestive organs, eyesight and chemoreception). In addition, larvae have to pass through different developmental stages with distinct properties. Therefore, larvae have limitations with regard to feed intake and digestion, which lead to feed requirements that are quite different from those in older life stages.

Firstly, they have a poorly developed larval gut until larval stage V to VI: i.e. a small hepatopancreas and a lack ofthe anterior midgut diverticulae (Deru 1990), which are the main sites for digestive enzyme production in the early stages ofpenaeid shrimp (Lovette &Felder 1990; Abubakr& Jones 1992). Hence, they have a very low trypsin activity and a very low digestive capacity. In contrast to penaeid larvae, they cannot digest artificial diets during that first feeding period and rely on a live food source which is highly digestible and may provide exogenous prey enzymes (Jones et al. 1993). More specifically, the live food should be zooplankton since M. rosenbergii is carnivorous during the first larval stages; however, from stage VII onwards the larvae become more omnivorous (Barros & Valenti 1997). Food is captured by the thoracic appendages (maxillipeds until stage III, and maxillipeds and pereopods in stages IV to XI). The capture of food is non-selective but its ingestion is a selective process (Barros & Valenti 1997).

Secondly, the early stages of M. rosenbergii are non-active hunters and, although they have a good visual perception (Daniels et al. 1992), they seem to capture food by chance encounter (Moller 1978). Live prey move continuously in the water column, thus increasing the chances of encounter but also providing an enhanced perception and extra chasing stimulus. In contrast, keeping artificial food particles in suspension requires a continuous agitation of the culture medium, which may damage the fragile larvae.

Thirdly, the size of the prey is important. At first feeding (stage II/III), prawn larvae can readily ingest newly hatched Artemia nauplii of the Great Salt Lake (GSL) strain (±500 |im in length). However, the cladoceran Moina mi-crura (±600 |im), which may be used as a cheap substitute or supplement for brine shrimp, is not taken up before stage IV (Alam et al. 1995a). On the other hand, Lovette & Felder (1988) demonstrated that the rotifer Brachionus plicatilis (±150 |im), a good zooplankton starter diet for marine fish and penaeid shrimp, is not a good diet for M. rosenbergii. Presumably the larvae spend too much effort in capturing sufficient numbers of rotifers to meet its nutritional requirements, resulting in an unfavourable energy balance.

The selection of a proper food source for the industrial production of prawn postlarvae (PL) is not only determined by the requirements of the predator. From the practical viewpoint of the culturist, a good diet should also feature a reliable and consistent supply, be cost-effective, and simple as well as versatile in application. The unique property of the branchiopod Artemia to form dormant embryos, so-called cysts, explains its widespread application as a convenient, suitable and excellent larval food source for freshwater prawn. It is therefore used in a vast majority of prawn hatcheries as well as in numerous other crustacean and fish hatcheries. Artemia cysts are harvested in large quantities from natural and semi-natural biotopes and, after processing and drying, are made available in airtight packing (cans, bags, buckets, etc.) as a storable 'on demand' live feed. Upon some 24 hours of incubation in sea-water, free-swimming Artemia larvae (nauplii) are released and can be directly fed as a nutritious live food, which makes them the most convenient, least labour-intensive zooplankton available for commercial aquaculture.

Forthese reasons, Artemia became universally accepted as preferred first-feeding live food in larval freshwater prawn rearing (New 1995). However, once the digestive system of the larva has further developed, allowing a high enzymatic activity (stage IV onwards), this diet is gradually supplemented or substituted with other live foods (e.g. Moina), and by farm-made larval diets or commercially prepared products.

How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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