Apparent digestibility of protein, energy, and amino acids in some selected feed ingredients for pacu Piaractus mesopotamicus

The apparent digestibility coefficients (ADCs) of amino acids (AA), protein, and energy in six feed ingredients (Brazilian fish meal, soybean meal, corn gluten meal, alcoholic yeast, corn, and wheat bran) we evaluated for pacu juveniles. In general, all ingredients showed high digestibility values for all AA, and differences among ADCs of individual amino acid were detected ( P  < 0.01). Corn gluten, soybean, and fish meals had the highest ADCs of AA. The ADCs of protein in fish meal, yeast, and corn gluten meal should not be used as AA digestibility indicators, because those showed differences up to 6.7% between the ADCs of protein and AA. All ingredients had lower ADCs of energy than corn gluten meal ( P  < 0.01). Lysine was the first limiting amino acid in fish meal, corn gluten meal, wheat bran, and corn, and the second limiting amino acid in soybean meal, as methionine was the first limiting amino acid in soybean meal and yeast. However, the soybean meal was the best quality protein source, as it had the highest digestible essential amino acid index. This demonstrated that digestible amino acid values can be used to formulate practical diets for pacu, preventing potential deficiencies or excess that might cause environmental and economic losses.     

A synopsis of smolt production in cages in a coastal freshwater lake in Norway

Abstract. Fish farming activities based on salmonid smolt production in cages were monitored in a coastal freshwater lake in western Norway. Yearly ongrowth in the fish farm increased from 350kg in 1979 to 15150kg in 1985, while maximum biomass of standing stock increased to nearly 14000kg in the same period. Maximum daily mortality observed was 0·37% of total stock in August 1983 due to an Ichthyobodo necator infection.
Except for 1983, between 61 and 73% of annual amount of feed was used in the second half of the year. Total feed amount used in 1979–85 was 77750kg. The phosphorous effluents decreased from 88 to 90% of the feed content to 80·4% in 1984–85.
A set of easily calculated parameters for judging management possibilities and success in cage farming is proposed: annual heat sum; mortality rate; growth rate; feed conversion; and phosphorous retention in fish.     

Morphological characterization and notes on the life cycle of a newly discovered variant of Loma salmonae (Putz, Hoffman & Dunbar) from a natural infection of chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Two variants of Loma salmonae occur in net-pen reared chinook salmon, Oncorhynchus tshawytscha. The typical variant (OA) has a host specificity for salmonids of the genus Oncorhynchus whereas the atypical variant (SV) has a host specificity for brook trout, Salvelinus fontinalis, and in this study, the ultrastructure of the two are compared. In fish at 8 weeks post-exposure xenomas of the SV variant have a very high proportion of mature spores compared with other developmental stages, while in xenomas of the OA variant there are fewer spores and many other developmental stages. Spores of the SV variant had up to 20 turns of their polar tube whereas those of the OA variant only had 17. Furthermore, the spores of the SV variant were significantly larger than those of the OA variant. The sporophorous vesicle for both variants appears to form around a sporogonial plasmodia, which results in many spores developing within the vesicle.     

Larval pigmentation, survival and growth of Penaeus indicus fed the nematode Panagrellus redivivus enriched with astaxanthin and various lipids

The highly unsaturated fatty acid (HUFA) content of the free-living nematode Panagrellus redivivus was successfully increased when three different lipid sources (cod-liver oil, marilla oil and capelin oil) from marine animals were used in the nematode culture medium. The lipid enrichment significantly increased the ω3 HUFA content, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), of the nematodes compared with lipid non-enriched nematodes. Penaeus indicus larvae fed the lipid-enriched nematodes had significantly ( P < 0.05) greater larval survival (69–77%) until metamorphosis than those fed non-enriched nematodes (54%).
This nematode species was also enriched with astaxanthin to determine the effects of this carotenoid on pigmentation, survival and growth during the larval development of P. indicus . The pigment, delivered via nematodes, significantly ( P < 0.05) improved larval coloration and survival (88%) compared with that of placebo-pigmented nematodes (78%). However, there was no strong evidence to show the benefit of either pigment and/or lipid enrichment on larval growth and development of P. indicus .
This study has shown that the nutritional value of the nematodes can be enhanced by the addition of fish oil into the culture medium. Supplementation of EPA and DHA, together with synthetic astaxanthin, allow the nematodes to be used as a sole diet for the larval culture of P. indicus .     

Protein metabolism during sexual maturation in female Atlantic salmon (Salmo salar L)

Body composition and fractional rates of protein synthesis (percentage of the protein mass synthesized per day) were determined in female Atlantic salmon returning to the River Tay, Scotland in July and in October after a 95 day period without food, during which time the animals became sexually mature. During the 95 day period of starvation/sexual maturation the ventricle and red muscle remained as a constant proportion of fresh weight whereas the liver, gill and ovary increased and the stomach and white muscle decreased. Fractional rates of protein synthesis increased markedly in the liver, stomach and ovary during the period of starvation/sexual maturation. In the gill, ventricle and white muscle fractional protein synthesis rates increased slightly or remained constant. From the estimated rates of protein loss or gain in the various tissues it is concluded that there is considerable protein turnover and repartitioning of amino acids during the period of starvation and sexual maturation. The absolute rate of protein synthesis rates in the ovary indicates that this tissue made the largest contribution to the energy and amino acid demands of the fish, whilst most of the amino acids required for maturation of the ovary were derived from white muscle, principally as the result of increased muscle protein degradation.     

Population ecology and prey consumption by fathead minnows in prairie wetlands: importance of detritus and larval fish

Abstract –  The fathead minnow Pimephales promelas occurs in high densities in wetlands of the prairie pothole region (PPR) of North America, but food resources sustaining these populations are poorly known. We assessed population dynamics and prey consumption of fathead minnow populations in three PPR wetlands for 2 years. Fish density peaked at 107 fish per m² for all age classes combined. Larval and juvenile fish dominated these populations in terms of abundance and accounted for 83% of total prey consumption. Detritus dominated fish diets, representing 53%, 40% and 79% of diet mass for larval, juvenile and adult fish respectively. Detritus consumption was positively related to minnow density and negatively related to invertebrate abundance, but only for adult fish. Seasonal production:biomass ratios were unrelated to proportions of detritus in the diet for all ages of fish, indicating that detritus is an important food resource capable of meeting metabolic demands and sustaining fish growth in high-density populations. Detritus consumption may also weaken links between abundance of invertebrate prey and minnows, promoting dense fish populations with strong, consistent influences on wetland ecosystems.     

Determination of the Sea Age of Atlantic Salmon in Scottish Catches from Length Composition Data

The importance of obtaining reliable estimates of the sea age composition of reported salmon catches are discussed. The use of length frequency distributions to determine the sea age of salmon in samples taken from the North Esk commercial catch are described. The results obtained using this technique are compared to those obtained from scale reading on a 4 weekly basis over a 16-year period. The use of length frequencies is shown to provide a reliable estimate of the sea age composition of catch samples. The adoption of this technique in catch sampling programmes is labour saving and facilitates rapid sampling.