
The "measure of the fish" and the fish prediction story data back to Pythagoras (c.520BC) and to the square root of three, and in an astro-theological sense before that.

The "measure of the fish" and the fish prediction story data back to Pythagoras (c.520BC) and to the square root of three, and in an astro-theological sense before that.

In religio-mythology, measure of the fish, aka “Jesus fish”, “Ichthus fish”, or “vesical piscis” (bladder of a fish), refers to []

Overview
In 2,500BC, the ratio 265/153, which is the height-to-width ratio of the intersection of two circles, supposedly, was known to the Egyptians as the closest whole number approximation of the square root of three √3. Some conjecture that 153 has something to do with pi and with the calculation of the design of the great pyramids at Cheops, in respect to its height and base leg. (Ѻ)

In 520BC, Pythagoras, according to the aretalogy, written by Porphyry (Ѻ), student of Plotinus (Ѻ), is reputed to have performed the supernatural feat of helping his disciples catch a large number of fish, number of fish not specifically stated:

“While at the Olympic games, he was discoursing with his friends about auguries, omens, and divine signs, and how men of true piety do receive messages from the Gods. Flying over his head was an eagle, who stopped, and came down to Pythagoras. After stroking her awhile, he released her. Meeting with some fishermen who were drawing in their nets heavily laden with fishes from the deep, he predicted the exact number of fish they had caught. The fishermen said that if his estimate was accurate they would do whatever he commanded. They counted them accurately, and found the number correct. He then bade them return the fish alive into the sea; and, what is more wonderful, not one of them died, although they had been out of the water a considerable time. He paid them and left.”
— Porphyry (c.280AD), Life of Pythagoras (§:25)

The number “153”, however, is inferred per reason that it is a sacred number in Pythagorean mathematics. [2]

In c.300BC, Euclid, in the first proposition of his Elements, gives a depiction of the vesical piscis, as the first step in constructing and equilateral triangle using a compass and a straightedge.

In 250BC, Archimedes, in his Measurement of the Circle, approximated the square root of three √3 as follows:

and was referring to the ratio 265/153 as the “measure of the fish”. [1]

In 150AD, the "Pythagoras fish catching story" was rescripted into the Bible, in John 21:11 (Ѻ), to the effect that Jesus miraculously, after he had been risen from the dead, helped his disciples catch a large number of fish, precisely 153, at the Sea of Galilee:

“Early in the morning, Jesus stood on the shore, but the disciples did not realize that it was Jesus. He called out to them, “Friends, haven’t you any fish?” “No,” they answered. He said, “Throw your net on the right side of the boat and you will find some.” When they did, they were unable to haul the net in because of the large number of fish. Then the disciple whom Jesus loved said to Peter, “It is the Lord!” As soon as Simon Peter heard him say, “It is the Lord,” he wrapped his outer garment around him (for he had taken it off) and jumped into the water. The other disciples followed in the boat, towing the net full of fish, for they were not far from shore, about a hundred yards. When they landed, they saw a fire of burning coals there with fish on it, and some bread. Jesus said to them, “Bring some of the fish you have just caught.” So Simon Peter climbed back into the boat and dragged the net ashore. It was full of large fish, 153, but even with so many the net was not torn. Jesus said to them, “Come and have breakfast.” None of the disciples dared ask him, “Who are you?” They knew it was the Lord. Jesus came, took the bread and gave it to them, and did the same with the fish. This was now the third time Jesus appeared to his disciples after he was raised from the dead.”
— Anon (c.150AD), Bible (John 21:4-14)

In 1836, David Strauss, in his The Life of Jesus: Critically Examined, digressed on the fish prediction stories of Pythagoras, as reported by Jamblichus and Porphyry, and Jesus. (Ѻ)

Astrotheology
In an astro-theological sense, Jesus symbolizes the age of Pisces which began around the time of his alleged birth. (Ѻ) Said another way, Pisces has been called the "dying god," where its sign opposite in the night sky is Virgo, or, the Virgin Mary. (Ѻ) Mary, is known to be associated with the star Sirius. The Egyptian equivalent of Pisces remains to be tracked down.

References
1. Freke, Timothy and Gandy, Peter. (1999). The Jesus Mysteries: Was the Original Jesus a Pagan God? (pg. 16). Three Rivers Press.
2. Jeremiah, Ken. (2014). Christian Mummification: An Interpretative History of the Preservation of Saints, Martyrs and Others (pg. 171). McFarland.

External links
● Ichthys – Wikipedia.
● 153 (number) – Wikipedia.
● Vesica piscis – Wikipedia.