How Temperature Affects Sex Ration of Red Cherry Shrimp

Today, I will tell you about temperature and how it can affect the Red cherry shrimp (Neocaridina davidi).

At last, we will have actual information from conducted researches. It can be extremely useful to those who are serious about shrimp breeding because it can help to have a certain type of control over the breeding process. 

The researches are not my own, and I do not claim any credits for them. That is why it would be fair to mention these works first:

• To what extent does temperature affect sex ratio in red cherry shrimp, neocaridina davidi? The scenario global warming to offspring sex ratio © by PSP Volume 26 – No. 12/2017 pages 7575-7579 Fresenius Environmental Bulletin.
• Effect of Temperature on Biochemical Composition, Growth and Reproduction of the Ornamental Red Cherry Shrimp Neocaridina heteropoda heteropoda (Decapoda, Caridea). Article in PLoS ONE March 2015.

While surfing the Internet in the quest to gain more knowledge about shrimp and shrimplets, I stumbled across two works about temperature effects on the shrimp. I combined them, and this is what I have now.

Conditions of the experiments

• Red cherry shrimp (about 1.5-2.0 cm), were evenly distributed to nine glass aquaria.
• Java moss was added in equal amounts to aquariums which had 5 cm of basalt sand on the bottom.
• The study was conducted as three replicates for each experimental temperature (20, 23, 26 C).
• Water temperatures were provided by aquarium heaters (Atman-100 W) with ±0.5°C precision.
• Females with eggs in the dorsal were taken into 8-liter containers individually after mating and observed twice a day. After hatching, females have not paired again. The dead larvae were immediately removed and noted.
• The pH was 7.5-8.0, the conductivity was 200-400 μS. The TDS (total dissolved matter) values were in the range of 100-200 ppm and oxygen >4 ppm. Lighting was provided for 12 hours by using an automatic
• The experiments with Red cherry shrimps lasted for 180 days at three different temperatures.

Temperature and sex ratio of the shrimp

Sex-determining mechanisms are broadly divided into two major categories: genetic and environmental. The most important environmental sex-determining factors are temperature and photoperiod. These environmental parameters stimulate and maintain gametogenesis and other reproductive processes in freshwater invertebrates.

Temperature and photoperiod are the two most important factors affecting gametogenesis. The temperature is also effective in the formation of gametes sex. As a result, the sex ratio changes depending on the temperature and the effects of different temperatures on the female/male ratio.

As the temperature increases, the number of males increases similarly. However, 28 and 32 ºC are risky for the growth and development of Red cherry shrimp, because at these temperatures they have a very high metabolism.

In addition, females could not keep the eggs at 32 ºC (89 ºF) and do not even get berried at all at 33 C (91 ºF). According to the latest observations, it is appropriate to grow these shrimps in the range of 21-23ºC (70-73 ºF).

On the graph, you can see the results of the experiments. It is obvious that the male/female ratio is dropping at higher temperatures. Therefore, in sex-dependent selective shrimp breeding, the temperature should be taken into consideration. Consequently, as temperature increases, the sex ratio of the offspring increases in favor of the male.

Note:

However, in another research (How Temperature affects Reproduction of Dwarf Shrimp), the female/male ratio at higher temperatures was not that catastrophic:

• 60 – 40 at 24 ºC (75 ºF)
• 55 – 45 at 28 ºC (82 ºF)
• 51 – 50 at 30 ºC (86 ºF)

Nonetheless, the tendency remains the same in all experiments. In my opinion, the reason behind these numbers lies in the nature of the shrimp.

During the rainy season, the freshwater will lower the water temperature in rivers and lakes. The rainy season means that there will be a lot of food. It is a natural signal of the optimum conditions for all creatures living in the water to breed.

Therefore, the shrimp population will grow fast hence, the females are the priority. On the contrary, during the dry season, the water temperature increases and the population needs to be sustained. As a result of surviving mode, more males appear. 

This natural trick is also noted with shrimp when doing a water change. If the water going into the aquarium is a little bit cooler compared to the water in the tank, it often can cause a bout of breeding. Of course, nobody says to put a bucket of ice water into the aquarium. It can simply kill the colony. Nonetheless, in case of a small difference, it can trigger the breeding.

Temperature and the egg (embryonic) development of the shrimp

Red cherry shrimps were kept for 180 days at three different temperatures. Egg development and larval output were monitored at 20, 23, and 26°C during the experiment. After three months, the sex of the offspring could be clearly determined.

The offspring from each experimental group were taken at the same temperature. The duration of egg incubation and the number of offspring were determined.

The experiment was conducted at three different temperatures. The result you can see on the graphic above. As the temperature dropped, the number of eggs decreased. At 20, 23, and 26°C. The researchers noticed that the female produced a maximum of 55 eggs.

Red zone: all the females that matured and mated at 32°C (90 ºF) lost their eggs. It indicates a potentially stressful effect of high temperature on ovarian maturation.

They also determined that the shortest embryonic development of the Cherry shrimp lasted for 15 days at 27°C (80 ºF) water temperature. Each female produced 21-51 larvae, large females produced more larvae, and larvae became an adult after 75 days.

Significant differences among temperatures for the hatching period were an expected result.

Egg development is accelerated with increasing temperature; increasing temperature decreases the output time of the eggs. The incubation period lasts between 25 and 37 days, depending on the water temperature.

This difference may be due to species variation or from the following phases. In the study, they calculated the time length between eggs transferred to females abdominal to grow as larvae.

Important: A decrease in the incubation period has also been associated with lower survival, higher energy consumption, and even serious deformities of embryos.

Note: It is also an important finding that cherry shrimp eggs are fertilized after each pairing, not paired females throw out the not fertilized eggs, and that they do not carry eggs from the dorsal (saddle) part to the abdomen.

Temperature Zones

Red temperature zone (27-32 C or 80-89 ºF) – expected higher juvenile/adult mortality, less egg survivability, individuals under temperature stress, with an impact on coloration seen. Warmer water will bring invertebrates to sexual maturity earlier but with smaller body size than if they had been brought up in the cold water.

Green temperature zone (23-26 C or 73-79 ºF) – expects or targets their optimum egg survivability and optimum individual well-being conditions are experienced. At the lower temperature range, we would expect that condensation issues could arise. It is known that at 25-24C, the coloration displayed is probably at the individual shrimps’ best.

Blue temperature zone (20-22 C or 68-71 ºF) – egg maturation takes longer, but reproduction will cease with colder temperatures. Cold water will also slow down sexual maturity. Consequently, the shrimp have longer to grow, thus, they will have a larger size at sexual maturity than if they had been brought up in warmer water.

Temperature and Survival rates of the shrimplets

The survival rates in the three groups (20, 23, 26°C) are not related to the temperature. Unfortunately, we have a significant decline at higher temperatures.

According to the observations, the temperature experienced during embryogenesis may influence larval biomass at hatching and subsequent larval development in decapods. Therefore, special care must be taken when the temperature is manipulated to accelerate embryonic development.

Conclusion

The female/male ratio is important to keep the natural balance and generation. An increase or decrease of temperature effects can sharply change the breeding and life cycle of the shrimp colony. Without the balance, growth disturbances, as well as disorders of egg development and embryo development, are likely to happen.

Water temperature is one of the most important physical factors affecting the survival and growth of shrimp. The growth rate increases with increasing temperature to a maximum, before declining near the upper thermal limit of tolerance. By manipulating this parameter, it may be possible to reduce the time needed to achieve the best result. However, high temperatures also increase mortality, possibly because less protein is incorporated into body tissues.

All these results of the experiments can be very useful for the shrimp breeders. Particularly, when they need to get more males (higher temperature) or go for more females (lower temperature).
I assume that 23-24 C (73-75 ºF) is the optimal temperature for Neocaridina shrimp. For more female shrimplets, all you need to do is just adjust the temperature in the aquarium to 21-22 C. In case of more male shrimplets, the best temperature will be around 26-27 C (79-81 ºF).

As I can see, a slight shift of 2-3 C (4-6 ºF) can play a crucial role in the formation of the shrimp colony. The good thing is that you can maintain the temperature you need only for a month, while the females are berried. After hatching, there is no need to keep shrimp in a temperature that is not ideal.

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