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Killifish : vivere all’estremo - Il giornale del mare
Skip to content Quando si dice “stile di vita non convenzionale”. Il Killifish ne è un esempio di vita. Cominciando dal nome. Il termine Killifish deriva dalla parola olandese kilde o kills che significa torrente . Termine usato dai conquistatori olandesi del Nord America per indicare i pesci che vivevano nei torrenti. Ma il Killifish non è un pesce che abita (soltanto) i torrenti. Sembra che la frase coniata “un pesce fuor fa’acqua ” faccia riferimento proprio a questi pesci che riescono a vivere per diverso tempo lontano dai corsi fluviali.
Un’innocua creatura?
Piccole creature innocue che misurano pochi centimetri, questi pesciolini sono stati adottati come specie domestiche allevate negli acquari di tutto il mondo. Ma la vita in natura non è cosi ordinaria come in acquario ed i killifish hanno tanto tanto da raccontare.
Un ciclo di vita bizzarro, breve (solitamente da poche settimane a meno di un anno), stili di vita “atipici” e strategie riproduttive diverse fanno di questo pesce un classico esempio di adattamento estremo.
I killifish riescono a vivere in pozzanghere dove la temperatura dell’acqua è elevatissima ed invece vi è una bassissima percentuale di ossigeno. Il Killifish riesce comunque a resistere, ma gli sforzi per continuare il cammino lo portano al breve ciclovitale.Non sono grandi nuotatori, anzi. La loro evoluzione li ha portati a vivere meglio con poca acqua. Alcune specie possono resistere addirittura sino a due mesi su terraferma, ma quando arriva la stagione secca questi pesci muoiono. Ma la vita deve continuare allora i killifish riescono a riprodursi in maniera unica in natura, soprattutto se parliamo di vertebrati. Il ciclo di vita velocissimo, crescono e diventano adulti in meno di 4 settimane, depongono le uova sino all’arrivo della stagione secca. Le uova resistono alla stagione secca in uno stato inattivo sepolti nel terreno . Una volta tornate le piogge le uova si schiudono e gli embrioni si sviluppano. Uno sviluppo che può anche andare in stand-by se le condizioni climatiche sono avverse. Questi pesci possono ritardare la crescita del cuore e del sistema circolatorio, ma anche dello scheletro e del sistema nervoso.
Il killifish delle mangrovie invece ha una caratteristica eccezionale per essere un vertebrato. E’ l’unico pesce ermafrodita in grado di auto-fecondarsi. E per evitare che la popolazione di kellifish sia fatta da cloni perfettamente identici, di tanto in tanto questi pesci si accoppiano con altri maschi ermafroditi che in questo caso fungono da femmine, proprio per rimescolare un po’ il patrimonio genetico.
E’ stato osservato che il killifish è anche un ottimo predatore. Riesce a cacciare grilli ed insetti fuori dall’acqua . Una specie, Hartii Rivulus , è in grado si compiere balzi fuori dall’acqua sino a 15 cm per catturare la propria preda.
Un altro, brunneus Rivulus , nativo delle mangrovie panamensi, riesce a “camminare” sull’acqua per scappare ai predatori.
Una vita estrema davvero.
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