I'm not sure you were all that wrong,
@Hampalong. Not sure about the quality of the source. However, I've had a hunt around and, although not convinced about the reputation of the source either (nutritiondata.self.com), I've had a look at courgette .v. cucumber nutritional value comparisons. NB. They refer to amounts per cup or half cup, which of course is much more than a human (or fish) would eat. Based on equal quantities of a cup, though, then:
vit.A, in IUs: courgette (248); cucumber (109) - courgette more nutritious.
vit.C in mgs: courgette (21.1); cucumber (3) - courgette more nutritious.
vit.K in mcgs: courgette (5.3); cucumber (17) - cucumber more nutritious.
folate in mcgs: courgette (36.0); cucumber (7.2) - courgette more nutritious.
calcium in mgs: courgette (18.6); cucumber (16.6) - courgette slightly more nutritious.
magnesium in mgs: courgette (21.1); cucumber (13.6) - courgette more nutritious.
phosphate in mgs: courgette (47.1); cucumber (25) - courgette more nutritious.
potassium in mgs: courgette (325); cucumber (152.

- courgette more nutritious.
sodium in mgs: courgette (12.4); cucumber (2.0) - courgette higher value.
Hope that's helpful - although not sure how much different species of fish need these vits and minerals!

Edited to add: although I eat it regularly, I didn't think cucumber had a smell at all - but then remembered what I considered a delicious smell and taste when I first tried it in a glass of water. So I'm afraid I'm in the other camp from Sue, Top Cookie and Mrs Matt.