Fish that live in the oceans lay more eggs than the fish that live in freshwater.
 
The rate of eggs hatching successfully, as well as the rate of survival for eggs are lower in seawater than in freshwater because eggs tend to get easily carried away by strong ocean current, or get eaten by other animals fairly often.
 
Also, there is a higher tendency for fish living in seawater to let their eggs drift away instead of laying eggs and attaching them onto seaweed etc. because the rate of successful egg hatching and the rate of survival after they hatch are lower if “eggs drift away in seawater”.The smaller the number of eggs that can survive through, the bigger the number of eggs that fish lay to increase the chance of eggs’ survival.
 
Here are the 15 types of [3] Fish that will appear in this card game “Babies?”.
 

with Japanese name	"Sea animals" or "flying animals"	Specific types of animals on the game cards
56.surfperch * 　ウミタナゴ	◎ sea
57.salmon 　サケ	◎ sea	chum salmon
58.cod　 　タラ	◎ sea	alaska pollock
59.conger eel 　アナゴ	◎ sea
60.red sea-bream 　タイ	◎ sea	Japanese sea bream
61.sardine 　イワシ	◎ sea	Japanese anchovy
62.mackerel 　サバ	◎ sea
63.tuna 　マグロ	◎ sea
64.herring 　ニシン	◎ sea
65.mullet 　ボラ	◎ sea
66.sturgeon 　チョウザメ	◎ sea
67.seahorse 　タツノオトシゴ	◎ sea
68.ocean sunfish 　マンボウ	◎ sea
69.carp　 　コイ
70.medaka 　メダカ

 

*Surfperch does not lay eggs, but rather gives live birth to babies.