Tropical Fish Capacitors are one of those obscure electronic components really only known about in the DIY electronics community. Even people with a passing knowledge of electronics likely wouldn't know. Even if you're opened up an off-the-shelf radio or a guitar pedal, you likely haven't ever seen one. So they fall into that obscure category with "Bumble Bee", "Wima", "Mustard", "Black Beauty" and "Vitamin Q" PIO capacitors.

Introduced to the market in 1964, they were also called "licorice allsort" capacitors which is equally fitting. More properly they are named Philips-Mullard C280 miniature metallized polyester film capacitors. They came in two voltage ratings, 250V and 400V wkg. Value coding is standardized with capacitors, but traditionally the colored stripes were vertical. Phillips flipped it horizontal like a flag, or a tropical fish. More here.  I think of them as tiny LGBTQ flags. You can read the the original data sheet HERE.

I suspect that a lot of their appeal is purely for the visual effect rather than just their function. But they do have some unique electronic properties. Polyester film has a high Dielectric constant, high dielectric strength and good temperature stability. Polyester aka polyethylene terephthalate (PET), is a pretty efficient dielectric. So they have a low equivalent series resistance (ESR) and are able to tolerate large fast spikes. [SOURCE]  I broke out their dielectric properties in the chart below:

Parameter	Value
Relative dielectric constant (@ 1MHz)	3.2
Dissipation factor at 1kHz (tan δ in %)	0.5
Insulation resistance (MΩ x µF	25,000
Dielectric absorption (%)	0.2
Capacitance drift (ΔC/C %)	1.5
Maximum temperature	125 °C / 257 °F
Temperature coefficient (ppm / °C)	+400 ±200
Moisture Absorption (%)	0.4

In application they're considered general purpose capacitors and they are most often employed in DC applications. So you will see them used for decoupling, DC blocking, bypassing and perhaps most notably for noise suppression. So you can find them in mode power supplies, electronic ballasts, RC snubbers and other filter circuits. You can find them in a number of audio applications. They're not perfect for every application, in terms of physical integrity they are not perhaps as tough as the Mullard ‘Mustard’ capacitors. Actually, the "tropyfish" caps are often derided as brittle. The first one I ever saw was in a wah-wah pedal which makes perfect sense, because it was broken.  

Mullard Ltd was founded in 1920 by Stanley R. Mullard, based in London; first in Hammersmith then Balham and later in Bloomsbury.  IN 1923 they formed a partnership with the Netherlands-based Philips N.V. (Yes, that Philips) Mullard finally sold all its shares to Philips in 1927 and it became just another part of that already large 36-year old conglomerate. But the Mullard division continued to operate and the brand persisted at least in the UK until 1988. Sovtek revived the brand name in 2007 for some thermionic tubes.

These capacitors and the company that originally made them were so favored among hobbyists there even used to be a fansite/ electronic store that focused on them: mullardmagic.co.uk. Sadly it is no more, but there are are a few captures on the way back machine. Mullard-style metallized polyester capacitors are still manufactured by Pennsylvania-based Vishay Intertechnology, but without the colorful horizontal stripes. More here.

The "C" in C280 stands for capacitor, and the 280 is the series type of the capacitor, the prefix commences with AE for  250V rating and CF for the 400V rating, and it always contains an M or K indicating uF and nF respectively. The numeral in between is a measure of the capacitance. The number C280AE/A330K = capacitor 280, 250v, 330 nF. Below I have made a chart of the various original Mullard models that were available:

TYPE	CAPACITANCE (uF)	CAPACITANCE (nF)	CAPACITANCE (pF)	WKG VOLTAGE
C280AE/A330K	0.33	330	330000	250
C280AE/A470K	0.47	470	470000	250
C280AE/A680K	0.68	680	680000	250
C280AE/A1M	1	1000	1000000	250
C280AE/A1M5	1.5	1500	1500000	250
C280AE/A2M2	2.2	2200	2200000	250
C280AE/P10K	0.01	10	10000	250
C280AE/P15K	0.015	15	15000	250
C280AE/P22K	0.022	22	22000	250
C280AE/P33K	0.033	33	33000	250
C280AE/P47K	0.047	47	47000	250
C280AE/P68K	0.068	68	68000	250
C280AE/P100K	0.1	100	100000	250
C280CF/A330K	0.33	330	330000	400
C280CF/A470K	0.47	470	470000	400
C280CF/A680K	0.68	680	680000	400
C280CF/A1M	1	1000	1000000	400
C280CF/P10K	0.01	10	10000	400
C280CF/P15K	0.015	15	15000	400
C280CF/P22K	0.022	22	22000	400
C280CF/P33K	0.033	33	33000	400
C280CF/P47K	0.047	47	47000	400
C280CF/P68K	0.068	68	68000	400
C280CF/P100K	0.1	100	100000	400
C280CF/P150K	0.15	150	150000	400
C280CF/P220K	0.22	220	220000	400