CHANNEL CATFISH INDUSTRY IN THE USA AND THE OFF-FLAVOR PROBLEM

Prikazani su povijest i razvoj tehnologije gojidbe kanalnog soma u ribnjacima te statistički podaci o proizvodnji, doradi i vrijednosti proizvoda u tijeku posljednjih 15 godina. Povećanje potrošnje u pučanstvu te sadašnje niske cijenež žitarica i soje povoljni su čimbenici za daljnje povećanje proizvodnje. Stalan razvoj industrije potiče nekoliko čimbenika: pionirski napori uzgajivača, istraživanja na sveučilištima i u državnim istraživačkim centrima od kojih neki imaju brojne pokusne ribnjake, rad kooperativne savjetodavne službe za ribnjačare, aktivnost udruga uzgajivača soma, suvremeni marketing, visoku kvalitetu proizvoda dorade i vertikalno povezivanje industrije. Neprikladna okusno-mirisna kakvoća soma uzrokovana metabolitima algi jedna je od glavnih poteškoća u industriji. Spomenuti su najvažniji rodovi algi koje proizvode takve metabolite, pojave mirisno-okusne neprikladnosti u drugih riba i u akumulacijama za pitku vodu, te sadašnji sustav sprečavanja dolaska kontaminirane ribe na tržište. Od nepoželjnih metabolita algi najvažniji su hlapljivi alkoholi geosmin i 2-methylisorborneol (MIB). Naglašena je potreba jeftinijih i bržih metoda određivanja tih metabolita. Istraživanja na Sveučilištu Arkansas u Pine Bluffu, SAD, o kontroliranju nepoželjnih vrsta algi u pokusnim ribnjacima s pomoću bijelog glavaša (Hypophthalmichthys molitrix Val.) i tilapija u kavezima pokazala su da taj pristup obećava uspješnost.The history, the production technology in channel catfish pond farming industry as well as the statistical data on production, processing and product value during past 15 years are presented. The trend of increasing consumption by the population and the presently low prices of grain and soybeans are conductive to further expansion of production. The steady growth of the industry is stimulated by several factors: innovative efforts by farmers, research at the universities and at government institutions some of which have numerous experimental ponds, cooperative extension service for farmers, modern marketing, activities of catfish farming associations, high quality of products from processing plants and vertical integration. The off-flavor in catfish caused by algal metabolites is a major problem in the industry. Genera of algae producing such metabolites, their accumulation in other fish and occurrence in drinking water reservoirs as well as the current emphasis on preventing the entrance of off-flavor contaminated catfish onto the market were reviewed. The main undesirable algal metyabolites are volatile alcohols geosmin and 2-methylisoborneol (MIB). The need for less expensive and quick methods of identifying major off-flavor compounds was pointed out. Research at the University of Arkansas at Pine Bluff, USA, on control of off-flavor algae in experimental ponds by filter-feeding silver carp (Hypophthalmichthys molitrix Val.) and tilapias confined in cages showed this approach to be rather promising

Observation of depictive versus tracing gestures selectively aids verbal versus visual–spatial learning in primary school children

Previous research has established that gesture observation aids learning in children. The current study examinedwhether observation of gestures (i.e. depictive and tracing gestures) differentially affected verbal and visual–spatial retention whenlearning a route and its street names. Specifically, we explored whether children (n = 97) with lower visual and verbal working-memory capacity benefited more from observing gestures as compared with children who score higher on these traits. To thisend, 11- to 13-year-old children were presented with an instructional video of a route containing no gestures, depictive gestures,tracing gestures or both depictive and tracing gestures. Results indicated that the type of observed gesture affected performance:Observing tracing gestures or both tracing and depictive gestures increased performance on route retention, while observingdepictive gestures or both depictive and tracing gestures increased performance on street name retention. These effects werenot differentially affected by working-memory capacit