Inactivated bacterins: contains inactivated or killed whole-cell fish bacterial pathogens
Live attenuated: live microorganisms (bacteria and viruses) modified so it would not progress to a disease
Subunit vaccines: contains small portion of fish pathogens
Toxoids: inactivated toxic compounds

Recombinant and DNA vaccines are also being developed with limited use due to unknown long-term effectiveness and varying regulations, respectively.

Different routes of administration are available as shown below:

	Description	Advantages	Disadvantages
Injection	Involves delivery through the muscle (intramuscular) or body cavity. Adjuvants are usually added to increase immune response.	Low volume of vaccine is needed Correct dose is ensured administered Long-term protection Applicable for multi-component vaccines	Labor-intensive Requires skilled personnel Have minimum size requirement
Immersion	Can be immersed in dips (short ~30 secs) or baths depending on concentration of vaccine	Cheap and easy to administer	Protection usually only short-term; second vaccination may be required
Oral	Delivery through the digestive system	Easily administered Minimal stress on fishes	Vaccine antigens should have protection (e.g., bioencapsulation) from gut

Development of Oral Fish Vaccines

Most of the vaccines for aquaculture to date are protective against bacterial pathogens. These can be administered either orally or by injection (intraperitoneal or intramuscular route). Injection route proves to be the most protective, but also labor-intensive, stressful to the fish, and reported for side effects. The main issue with oral vaccines, however, is due to low efficacy owing to harshness and tolerability of the fish gut environment.

Despite this issue, it is still ideal to develop oral vaccines that have the balance of protection from antigen breakdown and also immunological induction. Fish pathogen antigens for viral vaccines are propagated in cell lines but only limited yields are obtained. Esco VacciXcell bioreactors, CelCradle ® and TideXcell ®, allow maximum cell growth and increased cell population for adherent cell lines such as RTG-2 and CHSE-214 in fish vaccine manufacturing. These bioreactors allow the scaling up instead of scaling out of adherent cell culture.This is achieved through our macrocarriers that can house higher cell number per unit volume thereby.

To circumvent antigen degradation in the gut, microencapsulation techniques have been developed including nanoparticles (using chitosan nanoparticles), alginate particles (works well with DNA plasmids), biofilms (used against Aeromonas), and microalgae. Microalgae can function as a natural bio-encapsulation device that protects the expressed transgenes. It also allow scale-up production and consistent expression