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Biosynthesis of long-chain PUFAs (LC-PUFAs) in vertebrates involves sequential desaturation and elongation of C 18 PUFA, linoleic acid (LOA; 18:2n-6), and ␣ -linolenic acid (LNA; 18:3n-3) ( 1 ). Synthesis of arachidonic acid (ARA; 20:4n-6) and EPA (20:5n-3) from LOA and LNA, respectively, utilizes the same enzymes and pathways. The pre dominant pathway involves ⌬ 6 desaturation of LOA or LNA to 18:3n-6/18:4n-3 that are elongated to 20:3n-6/20:4n-3 followed by ⌬ 5 desaturation to ARA/EPA ( 1 ), but an alternative pathway with initial elongation of LOA or LNA followed by ⌬ 8 desaturation, an inherent ability of some ⌬ 6 desaturases, may be possible ( 2 ). Biosynthesis of DHA (22:6n-3) from EPA can also occur by two pathways. First, the so-called "Sprecher pathway" involves two sequential elongation steps from EPA to 24:5n-3 and a subsequent ⌬ 6 desaturation to 24:6n-3, followed by peroxisomal chain shortening ( 3 ). Second, a more direct pathway has been postulated in some marine fi sh that involves elongation of EPA to docosapentaenoic acid (22:5n-3) followed by ⌬ 4 desaturation to DHA ( 4,5 ).Dietary PUFAs are essential in fi sh, although requirements vary with species ( 6, 7 ). Generally, C 18 PUFAs can satisfy essential FA requirements of freshwater and salmonid species, but most marine fi sh have a requirement for LC-PUFAs such as EPA and DHA ( 8 ). Differing essential FA requirements have been linked to differences in the complement of fatty acyl desaturase (Fads) and elongase of very longchain FA (Elovl) genes ( 9-31 ). Thus, the dependence of Abstract Currently existing data show that the capability for long-chain PUFA (LC-PUFA) biosynthesis in teleost fi sh is more diverse than in other vertebrates. Such diversity has been primarily linked to the subfunctionalization that teleostei fatty acyl desaturase (Fads)2 desaturases have undergone during evolution. We previously showed that Chirostoma estor , one of the few representatives of freshwater atherinopsids, had the ability for LC-PUFA biosynthesis from C 18 PUFA precursors, in agreement with this species having unusually high contents of DHA. The particular ancestry and pattern of LC-PUFA biosynthesis activity of C. estor make this species an excellent model for study to gain further insight into LC-PUFA biosynthetic abilities among teleosts. The present study aimed to characterize cDNA sequences encoding fatty acyl elongases and desaturases, key genes involved in the LC-PUFA biosynthesis. Results show that C. estor expresses an elongase of very long-chain FA (Elovl)5 elongase and two Fads2 desaturases displaying ⌬ 4 and ⌬ 6/ ⌬ 5 specifi cities, thus allowing us to conclude that these three genes cover all the enzymatic abilities required for LC-PUFA biosynthesis from C 18 PUFA. In addition, the specifi cities of the C. estor Fads2 enabled us to propose potential evolutionary patterns and mechanisms for subfunctionalization of Fads2 among fi sh lineages. -GA-2010-276916, LONGFA). Additional funding was obtained from CONACYT, Mexico (INSAM FOINS 102/201...

An experiment was carried out with Cichlasoma urophthalmus (Günther) juveniles to determine the phosphorus requirement and its interaction with dietary calcium. Twelve isoenergetic and isoproteic diets were prepared using a basal artificial diet containing vitamin‐free casein, dextrin, starch, corn oil, fish oil, vitamin mixture and a mineral mixture free of calcium and phosphorus. Calcium and phosphorus levels were determined in the casein. To the basal diets were added different concentrations of phosphorus as potassium monophosphate (0.5, 1.0, 1.5 and 2.5 g kg–1) and calcium as calcium carbonate (0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0 and 4.0 g kg–1). These concentrations resulted in varying Ca–P ratios (1:1, 1.33:1, 1.5:1, 1.6:1 and 2.0:1). Calcium and phosphorus concentrations in the water were 84 mg kg–1 and 0.003 mg kg–1, respectively. The diet with 0.5 g kg–1 phosphorus resulted in deficiency signs such as reduced growth, high conversion ratio, high fat content and low bone mineralization. Increased levels of dietary calcium and phosphorus both gave improved growth and mineralization. Mineralization continued to increase with dietary phosphorus levels above that required for maximum growth. The optimum level of phosphorus in the diet was 1.5 g kg–1, the optimum calcium level was 1.8 g kg–1 and the optimum Ca–P ratio was 1.3. Carcass lipid levels were inversely related to dietary phosphorus.

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A 63  day–1 feeding trial was conducted under laboratory conditions to evaluate the effects of substituting animal protein with a mixture of plant feedstuffs including 25, 30, 35, 40 and 45% of the protein with torula yeast (Candida utilis), 20% with soybean meal and 15% with Alfalfa Leaf Protein Concentrate (ALC), in diets for tilapia (Oreochromis mossambicus Peters) fry. Feeding efficiency was compared against a diet with fish meal as the sole protein source. Diet nutritional quality was very similar independent of composition, with no differences in growth parameters, but fish fed with 30% yeast diet showed the best growth performance. Diet composition did not affect feed or protein utilization, with the best feed conversion ratio, protein efficiency ratio and apparent nitrogen utilization in the 25% yeast diet. Protein digestibility was above 80% for all diets, and no differences in carcass composition were observed. The best incidence cost was obtained with 25% yeast and the highest profit index with 30% yeast, but no statistical differences were observed with the other treatments. The results suggest that it is possible to replace up to 65% of animal protein with a mixture of plant proteins, including 30% from torula yeast, in tilapia fry diets without adverse effects on fish performance and culture profit.

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The feeding habits of the cichlid Cichlmoma urophrhalmus were studied in a brackish-water lagoon in Yucatan Peninsula, Mexico, from spring 1985 to spring 1986. The strong mandibular, maxillary and pharyngeal teeth, and the short intestine strongly suggest that C. urophfhulmus is primarily a carnivore. Subsequent gut contents analysis revealed that this species feeds principally on invertebrates throughout the year and that there were few differences between the five seasons studied. The algal material found in some stomachs may be consumed as a consequence of predation on small invertebrates, but the feeding structures and short intestine makes this species unable to digest vegetable materials efficiently. Differences with other cichlids used in aquaculture are discussed.