Usually, as he says in the bit you quote, Antonio is cash-poor but ship-rich. He has many ships, so he can afford to loose one. But in Act III, scene 1 we learn
Why, yet it lives there unchecked that Antonio hath a ship of rich lading wrack’d on the narrow seas; the Goodwins, I think they call the place, a very dangerous flat and fatal, where the carcasses of many a tall ship lie buried, as they say, if my gossip Report be an honest woman of her word.
and then in III,2 Antonio sends a letter to Salerio and Bassanio. Salerio reads it first and Bassanio asks
Hath all his ventures fail'd? What, not one hit?
From Tripolis, from Mexico, and England,
From Lisbon, Barbary, and India,
And not one vessel scape the dreadful touch
Of merchant-marring rocks?
(Here "not one hit?" means "not one succeeded?".) The answer: "Not one, my lord". That is, all six ships are lost. Later in the scene Bassanio gives a direct quote from the letter, summarizing
Sweet Bassanio, my ships have all miscarried, my creditors grow cruel, my estate is very low, my bond to the Jew is forfeit, and since in paying it, it is impossible I should live, all debts are clear’d between you and I, if I might but see you at my death. Notwithstanding, use your pleasure. If your love do not persuade you to come, let not my letter.
So he has lost all his ships, and so his credit rating is downgraded: is now not only cash-poor but also ship-poor.
But (spoiler alert) in the last scene it turns out, deus ex machina style, that all this shipping news was mistaken, and Antonio is ship-rich after all.
