Of course, as a general rule, the breeder should avoid brother-sister crosses at all costs. That applies to the professional aquaculturist and the home hobbyist alike. How important that is, and how soon inbreeding will cause serious problems if siblings mate, it tends to a large extent on the genotype. For example, when you are dealing with Mustangs and Sunbursts (Hippocampus erectus), you have a little leeway in that regard because those animals are the very epitome of hybrid vigor.
Ocean Rider’s captive-breeding programs for seahorses are geared very much toward increasing the heterogeneity of their livestock, not producing homozygous recessives. As intraspecific hybrids, Ocean Rider’s line of Hippocampus erectus enjoy increased vigor and benefit from enhanced genetic diversity compared to their wild-caught counterparts. Field studies show that there is very little immigration or emigration between seahorse colonies in the wild during the breeding season (Strawn, 1958; Vincent and Sadler, 1995). Likewise, once they’ve been extirpated locally, seahorses are notoriously slow to recolonize areas they have disappeared from. As a result, given their patchy distribution patterns and limited mobility, seahorses are prone to geographic isolation and there is relatively little gene flow between different populations in the wild (Vincent, 1990). Not so at Ocean Rider, where pairings between different bloodlines are a strict rule!
Basically, when they begin working with a particular species, Ocean Rider’s approach is typically to obtain sufficient broodstock from throughout their range to completely eliminate any concerns about inbreeding, and then to pair males and females from different bloodlines in order to achieve intraspecific hybridization. That way, each pairing actually increases the genetic diversity of the offspring, and providing you avoid brother-sister crosses when you subsequently select your breeders for the next generation, each new generation will actually be strengthened (more genetically diverse than their parents) through the phenomenon of hybrid vigor.
This is especially true considering the primary traits the Ocean Rider selects for are adaptability, disease resistance, vigor, aggressive feeding habits, and rapid growth. Far from being recessive characteristics that could eventually result in inbreeding, these are all adaptive traits that increase the line’s fitness and improve survivorship. In fact, they are the same sort of traits Mother Nature herself selects seahorses for in the wild to assure survival of the fittest. When nature culls out the weakest and least fit, it is known as "natural selection." It is nature’s way of keeping a species strong, vigorous, and adaptive (i.e., evolving to better fit its niche). The only difference is that Mother Nature is selecting for suitability to their natural habitat, whereas aquaculturists are selecting seahorses for fitness to captive conditions. In both cases, the selection process assures that the specimens become ever stronger and better adapted to their environmental niche, whether that is the aquarium or the ocean itself.
Practiced in this manner, selective breeding actually strengthens and improves a strain generation by generation, producing seahorses that are progressively hardier and better suited for aquarium life. This level of domestication not only improves their general health but also eliminates much of the stress wild seahorses experience in captivity, allowing cultured seahorses not only to live longer but to live better.
Initially, the breeders’ goal is not to rear the maximum number of offspring from each brood, but to assure that the weaker offspring are weeded out at every stage, and that only the fittest fry are selected for further rearing. As a result, it typically takes Ocean Rider several generations to strengthen a new line of seahorses in this manner before it is ready to bring to market.
It’s a good system: a multigenerational approach to rearing which assures that farm-raised seahorses will only continue to get stronger, hardier, and more trouble free over time as they become ever better adapted to aquarium conditions
Ideally, that’s the type of rearing program the home hobbyist should aim for as well. In actual practice, of course, that’s not possible because the home breeder is starting out with very limited numbers of broodstock. In many cases, brother-sister pairings cannot be avoided.
That is where the built-in genetic diversity and hybrid vigor of Mustangs and Sunbursts (H. erectus) pays dividends. For instance, I know one very successful home breeder who is now rearing fifth generation Mustangs from her original pair and her line is still going strong. If she had begun with less vigorous, less genetically diverse broodstock, she would be having serious problems with inbreeding by now.
So when it comes to inbreeding, the genotype of the broodstock you start with can make a big difference. If you’re starting with broodstock that don’t have the benefit of hybrid vigor, you can run into trouble in just two or three generations. For starters, there will be smaller broods and decreased survivorship among the fry. Undesirable recessive traits will begin to emerge. Eventually, the seahorses will simply stop breeding and the line will gradually die out.
Best of luck breeding and rearing your seahorses, Carver!