Side view of the front half of a zebrafish embryo that has been stained with an unknown in situ hybridization probe (in purple). You can see the yolk (dark tan) and the outline of the eye (slightly dark beige) in addition to the purple spot on the head. Credit staining to Thisse and Thisse et al. Image taken from ZFIN.

#GuessThatISH returns for 2026! This full nonsense game is sure to get you smiling 😜 Can you guess what this unknown ISH probe stains (in purple) on this #zebrafish embryo? WRONG ANSWERS ONLY! Bragging rights for the winner 😎 Bonus points if you can guess the gene. Happy guessing! #ThisseThursday 🧪

Dorsal view of a zebrafish larval that has been stained (in purple) with an unknown in situ hybridization probe. Parts of the brain are labelled, which looks suspiciously like something else.

Your favorite day of the week has arrived! Let's play #GuessThatISH 🤪 How would you describe the expression (in purple) of this #zebrafish larva? You know the drill: WRONG ANSWERS ONLY! The person with the most likes gets a free zebrafish sticker from Redbubble 🤩 Happy guessing! #ThisseThursday 🧪

Your favorite day of the week is here! Time to play 🤪 #ThisseThursday

Dorsal view of a zebrafish embryo that has been stained with an unknown in situ hybridization probe (in purple). There is some stuff labeled near the eyes that looks suspicious! Credit to Thisse and Thisse et al.

Encore! Encore! After a successful relaunch, we are back for more #GuessThatISH! How would you describe the in situ expression (in purple) in this zebrafish embryo? WRONG ANSWERS ONLY! The person w/ the most likes gets bragging rights and a virtual pat on the back 😎 Happy guessing! #ThisseThursday 🧪

Top view of an early stage zebrafish embryo that has been stained with an unknown in situ hybridization probe. Head to the left. Big opaque yolk to the right. Credit to Thisse & Thisse et al.

Your favorite guessing game has returned to social media! Here's how to play #GuessThatISH:

We present a pic of a #zebrafish embryo that has been stained using an unknown in situ probe by Thisse et al.

You tell us what it looks like! The catch? WRONG ANSWERS ONLY!

Let's play! #ThisseThursday 🧪

a man with glasses and a beard has the words it 's a very strong maybe above him Alt: a man with glasses and a beard has the words it 's a very strong maybe above him

#ThisseThursday comeback?

Lateral view of a two-day-old zebrafish embryo that has been stained with cb476 in situ hybridization probe. Many of the structures have been labelled with the corresponding tissue name.

If you've used @zfinmod.bsky.social, you may have noticed in situ expression data by Thisse et al. This comprehensive dataset was generated by Profs. Christine and (late) Bernard Thisse. In total, 8,400+ genes are described in 29,000+ figures at different stages. #ZebrafishFunFacts #ThisseThursday 🧪

Dorsal view of an early stage zebrafish embryo that has been stained (in purple) with an unknown in situ hybridization probe.

We've made it to another #ThisseThursday and that means it's time for #GuessThatISH! 😌 How would you describe the in situ staining (purple) in this #zebrafish embryo? WRONG ANSWERS PLEASE!!! The person with the most likes gets bragging rights and will be the envy of their peers 😏 Happy guessing! 🧪

Dorsal view of a zebrafish embryo that has been stained with an unknown in situ hybridization probe (in purple).

We've been struggling with #GuessThatISH but we will not be deterred! Let's play our favorite guessing game 😜 How would you describe the staining (in purple) in this #zebrafish embryo? WRONG ANSWERS ONLY! Bragging rights go to the winner so don't forget to vote 🙏 Happy guessing! #ThisseThursday 🧪

Dorsal view of a 48 hours post fertilization zebrafish embryo that has been stained (in purple) with an unknown in situ hybridization probe.

It's yet another #ThisseThursday so let's take a break and play #GuessThatISH! 🤪 How would you describe the expression (in purple) in this #zebrafish embryo? WRONG ANSWERS ONLY!!! The person with the most likes gets to brag about it to their colleagues and can add it to their CV 💪 Happy guessing! 🧪

Side view of a zebrafish embryo that has been stained with an in situ hybridization probe for titin

Let’s mix it up for #GuessThatISH this week! We assume that everyone knows what the “ISH” in GuessThatISH stands for. 💪 But for those that need a little help, please share what you think it is… One small twist: WRONG ANSWERS ONLY! Let’s get creative 🤪 Winner gets bragging rights! #ThisseThursday 🧪

Side view of an early stage zebrafish embryo that has been stained (in purple) with an unknown in situ hybridisation probe.

This week has flown by! Let's slow it down & play our favorite guessing game 😜 How would you describe the expression in this #zebrafish embryo? You know the drill: WRONG ANSWERS ONLY! The person w/ most likes gets bragging rights and a line of distinction on their CV! #GuessThatISH #ThisseThursday 🧪

Dorsal view of a zebrafish larva that has been stained (in dark purple) with an unknown in situ hybridization probe. Credit to Thisse and Thisse et al.

It's been FOUR years since the first #GuessThatISH post on social media 🍻 We can't think of a better way to celebrate than to play another game! How would you describe the staining in this #zebrafish larva? WRONG ANSWERS ONLY! The person w/ most ❤️ gets a free fishy mug ☕ LET'S GO! #ThisseThursday 🧪

Side view of an early stage zebrafish embryo that has been stained (in purple) with an unknown in situ hybridization probe.

We nearly forgot!!! Time to get creative and play #GuessThatISH 🤪 🧪 How would you describe the staining (in purple) in this #zebrafish embryo? WRONG ANSWERS ONLY! The person with the most likes by the weekend gets bragging rights and a small heaping of brine shrimp 🦐 Happy guessing! #ThisseThursday

Image of an early somite-stage zebrafish embryo that has been stained (in purple) with an unknown in situ hybridization probe.

Your favorite day of the week has arrived! Time to play #GuessThatISH 😜 How would you describe the expression in this early #zebrafish embryo? WRONG ANSWERS ONLY! The person with the most likes secures bragging rights for the week and can write a line on their CV 🤩 Happy guessing! #ThisseThursday 🧪

It’s #ThisseThursday, an ode to #zebrafish legends Christine Thisse and the late Bernard Thisse! Time to play 🤪

Dorsal view of a zebrafish embryo that has been stained (in purple) with an unknown in situ hybridization probe.

ENCORE! We've heard the rave reviews from the first #GuessThatISH so we are back for more 😜 How would you describe the staining in this #zebrafish embryo? WRONG ANSWERS ONLY! The person with the most likes gets bragging rights and a line of distinction on their CV 😏 Happy guessing! #ThisseThursday 🧪

Dorsal view of a zebrafish embryo that has been stained (In purple) with an unknown in situ hybridization probe. Credit to Thisse and Thisse et al.

As seen on Twitter, #GuessThatISH makes its debut on Bluesky 🤩 Get your thinking caps on because this first one is a fin-flapper 💪 How would you describe the expression in this #zebrafish embryo? WRONG ANSWERS ONLY! The person w/ the most likes gets bragging rights. Happy guessing! #ThisseThursday 🧪

Frontal view of a two days post fertilization zebrafish embryo. It has been stained with an unknown in situ hybridization probe.

The year has been building towards this moment! It's time for the final #GuessThatISH of 2023 🥂 How would you describe the expression (in purple) in this zebrafish embryo? WRONG ANSWERS ONLY 😜 The person w/ the most likes on Bluesky gets a special commendation and a line on their CV! #ThisseThursday

Lateral view of an epiboly-stage zebrafish embryo that has been stained with an unknown in situ hybridization probe.

Your favorite time of the week has arrived! It's time for #GuessThatISH 🤪 How would you describe this #zebrafish embryo? WRONG ANSWERS ONLY, PLEASE 🙏The person with the most likes gets bragging rights on Bluesky and a small morsel of brine shrimp 🦐🦐🦐 Happy guessing! #ThisseThursday 🧪