The precise number has prompted discussion of the symbolism over time. The Orthodox Study Bible mentions, without citation, that it reflects symbolically all nations, caught by the “fishers of men” sent by Jesus with the Holy Spirit to evangelize the world. This apparently comes from the count in Genesis after Noah’s Flood of 70 nations, or 7 x 10, a number of completeness involving the days of Creation and the Ten Commandments, whose constituents add up to 17. In turn, the number 153 it is noted by commentators is a number that is the sum total of all the numerals 1 through 17. St. Theophylact in his Byzantine Gospel commentaries saw the number as symbolizing the catching of the Gentles in evangelism (represented by the number 100) and the Jews (represented by 50) alongside the number 3 for the Holy Trinity. St. Jerome earlier had posited that this was the number of all the species of fish in the world, 153. Some current-day discussions can be found here and here.