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Lo squalo salmone – Lamna ditropis - Il giornale del mare
Skip to content Lo squalo salmone riesce ad elevare la propria temperatura corporea anche di oltre 10°C rispetto a quella dell’acqua. Se è vero che l’unico pesce a sangue scoperto sino ad oggi è l’Opah è anche vero che esistono diverse specie che possono aumentare la temperatura corporea interna sino a superare la temperatura dell’ambiente in cui vivono. Un processo conosciuto da tempo, quello dell’endotermia , ma che ancora non aveva trovato risposta al perchè.
Un nuovo studio pubblicato dalla National Academy of Sciences degli Stati Uniti d’America, dimostra che pesci endotermici come tonni e squali bianchi, nuotano due volte e mezzo più veloce rispetto a pesci di stesse dimensioni a sangue freddo.
Un team internazionale di ricercatori ha condotto lo studio collegando diversi sensori sugli squali salmone( Lamna ditropis) e ha confrontato le informazioni precedentemente ottenute da altri pesci a sangue freddo. I risultati hanno stabilito che i pesci endotermici sono in grado di nuotare più velocemente di quanto facciano pesci ectotermi (a sangue freddo) di dimensioni simili di dimensioni simili ectotermi.
Nuotare per alzare la temperatura corporea
Essere agili in acque fredde, risulta possibile solo mantenendo una temperatura corporea maggiore dell’acqua circostante, e lo squalo salmone non dispone ne della pelliccia degli orsi, ne delle riserve di grasso dei grandi cetacei. Ma lo squalo salmone dispone della rete mirabile , un insieme di arterie e vene che si trovano vicinissime le une alle altre, in grado di scambiarsi calore, attraverso le pareti dei vasi. In questo modo, si attua un gradiente di temperatura tra i flussi sanguigni arteriosi e venosi controcorrente, che consente allo squalo salmone di mantenere una temperatura corporea superiore anche di 10 °C a quella dell’ambiente circostante.
Lo squalo salmone Il metabolismo dello squalo salmone dunque, è tale da richiedere cibo regolarmente e in abbondanza, e proprio nella stagione calda, quando le prede abbondano, esso da il meglio di se. Come detto, un gran numero di esemplari si radunano presso le foci e gli estuari. I grandi gruppi tuttavia, non sembrano affatto organizzati, anzi ognuno agisce autonomamente; essi si adagiano sin quasi sul fondo, un po’ come fanno gli squali bianchi e, individuata la preda, non la perdono più di vista e dopo poco tempo, sferrano l’attacco verticalmente, dal basso verso la superficie, compiendo dei balzi spettacolari. Dopo le orche, gli squali sono i predatori più grandi delle acque della costa ovest del nord America; i maschi possono raggiungere i 3 metri di lunghezza, le femmine dimensioni anche maggiori. Le dimensioni, la possanza e le caratteristiche predatorie, fanno si che lo squalo salmone possa essere pericoloso per l’uomo, anche se gli incontri sono rari, dal momento che la temperatura media della zona ove la specie è maggiormente presente è decisamente bassa, abbastanza da scoraggiare un bagno.
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