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Il più grande pesce d’acqua dolce del mondo - Il giornale del mare
Skip to content Lo storione beluga Huso huso è il pesce d’acqua dolce più grande del mondo, più grande del pesce gatto gigante del Mekong Pangasianodon gigas ! In effetti, si pensa che sia il più grande pesce d’acqua dolce che sia mai vissuto.
È una specie anadroma originaria dei bacini del Caspio e del Mar Nero, ma ora è in pericolo di estinzione a causa degli impatti antropici, dell’inquinamento e della pesca eccessiva. Dalle uova di Beluga viene prodotto uno dei caviali più costosi . La colla di pesce, che è stata utilizzata nella produzione della Birra Guinness, è anch’essa ricavata dallo storione. Lo storione Beluga era un tempo abbondante e intraprese vaste migrazioni sul Volga e sul Danubio, i fiumi più grandi d’Europa.
Uno storione Beluga record fu catturato nell’estuario del Volga nel 1827 e pesava 1.571 kg! Lo storione Beluga può vivere per oltre un secolo (età accertata, 118 anni), alcuni individui potrebbero essere stati generati in habitat ora bloccati dalle dighe costruite da Stalin sul Volga e dalle dighe Iron Gates (1972-1985) sul Danubio.
Lo storione Beluga intraprende un’importante migrazione riproduttiva (Migrazione anadroma) a monte per deporre le uova. Entra nei fiumi in primavera e in autunno. La deposizione delle uova varia da 0,36 a 7,7 milioni di uova, tuttavia le femmine maturano tardi (intorno ai 18 anni) e depongono le uova solo una volta ogni 5-7 anni. in primavera e meno frequentemente in autunno. Il numero di uova per femmina può essere assai elevato, fino a 7,7 milioni. Ogni femmina produce una quantità di uova pari a circa il 10% del proprio peso. Il numero delle uova è di 30-35000 unità per kg.
L’habitat riproduttivo è nel corso principale di grandi fiumi profondi con forte corrente e su substrato di pietra o ghiaia. I giovani si trovano in habitat fluviali poco profondi durante la loro prima estate. Il giovane Storione Beluga migra poi verso il mare dove si nutre principalmente di pesci ed invertebrati. Gli esemplari vecchi e sterili, si ritirano in mare a profondità di 70-90 m e non risalgono più le acque dolci.
fiume Ural Il fiume Ural in Kazakistan è ora l’unico fiume che sfocia nel Mar Caspio che non ha una diga che blocchi la migrazione di questo grande pesce
Conservazione Sono in corso programmi di ripopolamento dello storione beluga, ma questi non compensano la perdita della riproduzione naturale e le popolazioni continuano a diminuire.
Il numero annuo di avannotti liberati nel Volga ogni anno è di circa 3 milioni, e di circa 20.000 nel Danubio. Una certa riproduzione naturale della specie rimane nei fiumi Volga e Ural. Si è tentato di creare zone di riproduzione artificiale sotto la diga di Volgograd sul fiume Volga, con scarso successo. Il fiume Ural in Kazakistan è ora l’unico fiume che sfocia nel Mar Caspio che non ha una diga che blocchi la migrazione di questo grande pesce. Questo è un fiume chiave per garantire la sopravvivenza di questa specie.
Immagine di Charlene N Simmons via FLIRCK Gli storioni sono un gruppo di pesci molto antico (oltre 200 milioni di anni) e costituiscono uno dei ceppi più primitivi di pesci ossei. Tuttavia, la maggior parte delle specie di storione è ora in pericolo.
Lo storione beluga è incluso nell’elenco delle specie minacciate di estinzione che figurano nella direttiva 92/43 CEE; Sul territorio Italiano ne è vietata la pesca, anche se non sono intraprese azioni per l’incremento della specie.
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