Eating fish without picking on thorns is expected to become the standard in the diet

After the realization of seedless melons and seedless grapes, today, the stickleback fish is also "swimming" to the table
.
In the future, fish bones stuck in the throat may become history, and eating fish without picking on will become the standard in the diet
.

Recently, the team of Professor Gao Zexia of the College of Fisheries of Huazhong Agricultural University revealed the latest research progress: using the first generation of heterozygous (F0 generation) less stickleback, the Wuchang fish (F1 generation) seed (F1 generation) without intermuscular spines has been bred through male and female mating, and the genetic stable breeding of non-muscular stickleback (hereinafter referred to as "stickleback") is being further carried out
.
According to the relevant procedures, after the new germplasm traits are stable and the relevant national certification is obtained, the stickleback can be promoted
on a large scale.

How do you stop a fish from growing spines? Where did all the bones of the stickless fish go? In terms of taste, how does the taste of stickleback fish differ from that of stickleback? In addition to Wuchang fish, can the research results be applied to other bulk freshwater fish?

Find thorns to reveal the law of intermuscular ossification in fish

Tuantou bream, also known as Wuchang fish, is one of the main freshwater fish farmed in China, with delicious meat and full flavor
.
As early as 2008, Gao Zexia's team carried out the genetic selection of
the group head bream.
At that time, the team focused on related traits
such as growth, disease resistance, and hypoxia tolerance.
In 2012, the team began to pay attention to the intermuscular spines, and the idea
of changing the characteristics of the intermuscular spines of the bream was born.

The bream has more intermuscular spines, which brings great inconvenience
when eating.
Not only that, the existence of intermuscular spines limits the high-quality development
of the seed industry and industry of the bream to a certain extent.
In the process of breeding the bream, Gao Zexia's team collected data from many sources and learned that the intermuscular spines had a great impact
on the food safety, production and processing value of the bream, and even a variety of mainly farmed spiny fish at home and abroad.

"Many members of the team, including me, have had the experience
of eating Wuchang fish and getting stuck in the throat by fish bones.
" Gao Zexia said, "The team hopes to help improve the quality
of the seed industry of stickleback in China by solving the small problem of fish bones 'stuck throat'.
" Through the breeding research of the spinless bream, let everyone eat fish safely, eat fish with confidence, and eat fish happily
.
”

Where do the thorns come from? How do the thorns grow over time?

Finding a thorn became the first problem
that Gao Zexia's team had to figure out.

Gao Zexia's team determined that when the body length of the bream is about 1.
33 cm, that is, about 20 days after the membrane emerges, the intermuscular spines begin to appear, and the intermuscular spines grow sequentially from tail to head
.
This was the beginning
of research on the selection of the non-intermuscular spiny bream.

When Gao Zexia's team compared fish with different swimming patterns, they found that the ossification order of the intermuscular spines of the bream was not accidental
.
The team's results showed that there was a certain relationship
between swimming patterns, the order of occurrence of intermuscular spines, and the complexity of intermuscular spine types.
Using a variety of histological methods, the team determined that the ossification of the intermuscular spur is intramembranous ossification and does not go through the cartilage stage
.

By extracting high-quality ribonucleic acid (RNA) from intermuscular spiny tissues and using high-throughput sequencing technology, the team carried out multi-omics analysis of transcriptome and proteome at different stages of intermuscular spines, gene expression and protein expression differential analysis between intermuscular spines and other bone tissues, clarified the regulatory role of different signaling pathway genes in the occurrence and development of intermuscular spines, and screened and identified a number of key candidate genes
to regulate the occurrence and development of intermuscular spines.

The law of intermuscular spinning in fish revealed by Gao Zexia's team provides a clearer direction
for exploring the molecular mechanism of the occurrence and development of intermuscular spines in bream and fish.

Pick and pinch, identify trait changes that are important for influencing genes

At first, Gao Zexia's team used two modern molecular breeding technologies, molecular marker assistance and gene editing, to carry out the genetic improvement
of the intermuscular spiny trait of the bream.

When the key genes regulating the occurrence and development of intermuscular spines in fish were not identified, Gao Zexia's team hoped to use molecular marker-assisted breeding technology to select varieties
with a small number of intermuscular spines.

Gao Zexia's team found that individuals with at least 84 spines and a maximum of 146 spines in the breeding population, and for the first time evaluated the heritability of the trait of the number of intermuscular spines in fish, and screened out SNP sites that were significantly related to the number of intermuscular spines in Lumphead bream
.

Gao Zexia's team said that at first, they started from zebrafish and used a variety of gene editing techniques to analyze the regulatory effect of more than 60 candidate genes on the occurrence and development of intermuscular spines in zebrafish, and found that three genes regulated the occurrence and development
of intermuscular spines in fish to varying degrees.

Among them, SCXA and BMP6 gene function loss will lead to a significant reduction in the number of intermuscular spines in zebrafish, but these zebrafish often have defective problems
.
However, RUNX2B mutation did not significantly affect
the individual growth, formation of other bone units, muscle fatty acid and amino acid content of zebrafish under the premise of complete loss of intermuscular spines.

The Runx2b mutated zebrafish strain has a very stable genetic trait, and the offspring all exhibit a stable phenotype
with complete loss of intermuscular spines.

Later, the team applied the molecular breeding-gene editing technology system to the bream, officially taking the first step in exploring the
stickless fish.

In 2020, the team explored the CRISPR/Cas9 gene editing technology of the grouphead bream; In 2021, the runx2b gene editing experiment of the group head bream was officially carried out, and the F0 generation gene editing group head bream was obtained; This year, the team further selected male and female individuals with mutations in the F0 generation to mate and breed the F1 generation group, and screened individuals with no intermuscular spines at all
.

At present, the growth traits of the non-intermuscular spiny bream are good, and the average weight of the 5-month-old non-spiny bream is 50 grams
.
With the naked eye, there is almost no difference
in appearance between the thornless Wuchang fish and the same length thorny Wuchang fish.
In the X-ray, the thorny Wuchang fish has rows of small intermuscular thorns growing horizontally in the body, while the thornless Wuchang fish has a dark shadow in the body, and the fish bones
cannot be seen at all.

Without thorns, the "new fashion" of eating fish still needs time to develop

In the past 10 years, the aquaculture output of China's group head bream has been between
700,000 and 800,000 tons.

Gao Zexia's team believes that it is worth trying and is very meaningful
to promote the further development of the seed industry and breeding industry of Tuantou bream, improve its intermuscular spine traits and improve its edible and processing value through scientific and technological means.

At present, the thornless bream studied by Gao Zexia's team has not yet entered the stage of large-scale breeding
.
Gao Zexia's team introduced that if the intermuscular bream cultivated in the later stage can pass the national approval, it is hoped that it can cooperate with the system test station, the local aquatic technology extension station, the tuantou bream seed breeding farm, the tuantou bream breeding cooperative, etc.
, to jointly promote the transformation and upgrading
of the tuantou bream seed industry and breeding industry.

Gao Zexia's team said that production promotion needs to undergo strict experimental breeding evaluation
.
The growth indexes, muscle quality and other indicators of each generation of intermuscular spiny bream also need to be carefully evaluated
.
In addition, the establishment and promulgation of relevant germplasm resource systems need to be established and implemented before productive promotion
can be considered.
Stickless fish "swim" from the laboratory to the table, and many aspects of research
are still needed.

Through this technology, Wuchang fish bid farewell to "spiny more", is it also feasible on other spiny fish? Gao Zexia's team hopes to build a modern aquaculture model such as factory circulating water aquaculture by carrying out research on the culture mode and nutritional requirements of new germplasm of the non-muscular spiny bream, and cooperate with other interested scientific research teams or enterprises to carry out cooperative research
on the cultivation of new germplasm without intermuscular spines in other spiny fish.

The bream itself is a species of carpinid
.
Gao Zexia's team believes that carps such as green, grass, silver carp, bighead, carp, crucian carp and bream have the same type and the same formation method of intermuscular spines as the grouphead bream, and are the same carps, which have high similarity in genome sequence with the grouphead bream
.
Therefore, it is theoretically feasible
to breed these intermuscular spiny species of carps.

At present, Gao Zexia's team has obtained the F0 generation mutant of grass carp, and has made good progress
in improving the intermuscular spiny traits of grass carp, silver crucian and silver carp and other fish species.

China Food News(November 10, 2022, Version 08)

(Responsible editor: Wang Jiayi)