Tuesday, July 19, 2016

Barramundi/Sea bass - Lates calcarifer

Taxonomic and biological features:

Distinguishing characters
Body elongated, compressed. Mouth large, slightly oblique, upper jaw extending behind the eye (Figure 1). Dorsal fin with 7 to 9 spines and 10 to 11 soft rays. Pectoral fin short and rounded. Dorsal and anal fins both have scaly sheath. Anal fin round, with three spines and 7–8 soft rays. Caudal fin rounded. Scales large and ctenoid. Teeth villiform, no canine teeth present. Lower edge of preoperculum with strong spine; operculum with a small spine and with a serrated flap above origin of lateral line (Kungvankij et al., 1985).

Barramundi is a protandrous hermaphrodite. Males mature at about four years of age and change sex at about seven years (85–100 cm TL (Total Length)), becoming functional females (Moore, 1979). Some primary females may be present (Moore, 1980). L. calcarifer is a catadromous fish, inhabiting rivers before returning to estuaries to spawn. Spawning occurs in brackish water and larvae (1.5 mm) passively drift into coastal swamps.

Juveniles migrate upstream and sub-adult fish remain in freshwater until they reach sexual maturity. Maturing males migrate downstream during the spawning season (Russel and Rimmer, 2004) 

Natural food and feeding habits
The mouth and gut develop the day after hatching. The larvae first live on their yolk sac and commence exogenous feeding on zooplankton at 45 to 50 hours after hatching (Kohno et al., 1986).

L. calcarifer is an opportunistic predator with an ontogenetic shift in the diet. Fish less than 40 mm feed almost exclusively on microcrustacea. With increasing fish size, this food type is progressively replaced by macrocrustacea, other invertebrates and fish (Davis, 1985)

Kungvankij et al. (1985) found that the stomach content of fish greater than 200 mm consisted of 70 percent crustaceans (such as shrimp and small crab) and 30 percent fish, while Davis (1985) observed that fish above 300 mm feed almost exclusively on fish, reaching 80 percent of the diet in the largest fish.

L. calcarifer is a suction feeder and prey is swallowed whole. There is a positive correlation between predator and prey length - the latter can reach 60 percent of predator length (Davis, 1985). Cannibalism is a common occurrence and hence it is necessary to grade the fish on a regular basis.

In the wild, Barramundi shows a distinct seasonal growth pattern. Maximum growth occurs at the start of autumn, down over winter and reaches a minimum at the beginning of spring (Xiao, 2000). The von Bertalanffy parameters describing the growth of seabass are L∞=690 mm, K =0.53, to=0.003 (Stuart and McKillup, 2002).

In captivity, growth depends on various factors including feeding rate, feed quality, stocking density and temperature (optimum between 28 and 32°C). In Australia, at suboptimal temperatures (22–27°C), 500 g barramundi are produced in one year in tanks, while 800g fish are obtained within the same period at higher temperatures (Tucker, 2001). Two years are generally required to produce 3 kg fish (Russel and Rimmer, 2004). There are no significant differences in growth rate in either fresh or salt water (MacKinnon, 1990 cited in Russel and Rimmer, 2004). Normal market size is in the range 250–600 g, but it is economical to raise the fish to 3 kg or more (Tucker, 2001).

Nutritional requirements
Protein and Essential Amino Acids (EAA)
Optimal dietary protein content has been shown to vary with dietary energy levels and the size of fish. Most studies suggest a crude protein (CP) requirement between 45 percent and 55 percent (Glencross, 2006). Requirements for protein and amino acids decreases with increasing fish size according to the change in energy demand of the fish. Glencross (2003) determined a digestible protein requirement of 56, 42 and 31 percent at a DE content of 15kJ/g for 10, 100 and 1000g fish, respectively. Protein utilisation efficiency has been estimated at 46–50 percent (Williams and Barlow, 1999; Lupatsch, 2003). Nankervis & Southgate (2006b) have shown that the optimum diet for L. calcarifer larvae from 14 to 28 days post–hatch (DPH) should contain 50 percent protein and a minimum of 21 kJ/g dietary energy. Some EAA requirements have been determined.

Lipids and essential fatty acids
Best performance by 80g fish was obtained with a diet containing 18 percent lipid and 60 percent protein and protein retention may be improved with increased lipid levels (Williams et al., 2003a). Survival at metamorphosis is influenced by ω3 Highly Unsaturated Fatty Acids (HUFA) levels in the live food (20:5 3, 22:6ω3) (Rimmer et al., 1994; Dhert et al., 1990). Dietary n-3 fatty acids levels of 1.0 percent have been recommended for juvenile fish (Wanakowat et al., 1993). Williams and Barlow (1999) suggested an optimal ratio of n-3 to n-6 fatty acids of between 1.5 and 1.8:1.

Barramundi have shown limited capacity to utilise dietary carbohydrates for energy. Starch digestibilities are below 30 percent at even low inclusion levels (Anderson, 2003; cited in Glencross, 2006). However, for juvenile barramundi Catacutan and Coloso (1997) showed that carbohydrates have a sparing effect for lipid as an energy source in practical diets. They recommended a dietary carbohydrate level of 20 percent for diets containing lipid levels ranging from 6 to 18 percent with 42.5 percent CP.

Vitamins and minerals
Certain dietary vitamins have been identified as essential for barramundi. Those that have not been specifically identified are still thought to be required and this is consistent with findings from other fish (Glencross, 2006). Vitamin C requirement is 500–700 mg/kg of diet (Boonyaratpalin et al., 1989; 1994) or 25–30 mg/kg of diet using crystalline ascorbic acid or ascorbyl-2-monophosphate-magnesium, respectively (Phromkunthong et al., 1997). Wanakowat et al. (1989) have shown that 5 mg/kg diet of pyridoxine was required for normal growth and 10 mg/kg for normal lymphocyte levels. Pantothenic acid requirement is 15 mg/kg diet for normal growth (Boonyaratpalin and Wanokowat, 1993). Dietary phosphorus requirement ranges between 0.55 percent and 0.65 percent (Boonyaratpalin and Phongmaneerat, 1990). T he addition of salt (NaCl) to the diet at a level of up to 4 percent has been reported to generate a better feed utilization (Harpaz et al., 2005b).

Energy utilisation by barramundi has been estimated as 68 percent (Lupatsch, 2003). Based on the changes in somatic demand for energy by the fish, Glencross (2006) suggested a lower-energy, higher-protein diet (15 kJ DE/g, 50 percent CP, 14 percent lipid) for small fish (<200g), and a lower-protein, medium-energy diet (17 kJ DE/g, 46 percent CP, 20 percent lipid) for large fish (>200g).

At 20–22°C a feed high in DE (19 kJ/g) and a digestible protein to DE ratio of 22.5 g/MJ was recommended by Williams et al. (2006) to improve productivity.

Source: www.fao.org

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