Ink From Longfin Inshore Squid, Doryteuthis pealeii, as a Chemical and Visual Defense Against Two Predatory Fishes, Summer Flounder, Paralichthys dentatus, and Sea Catfish, Ariopsis felis

Abstract

Abstract. Chemical and visual defenses are used by many organisms to avoid being approached or eaten by predators. An example is inking molluscs-including gastropods such as sea hares and cephalopods such as squid, cuttlefish, and octopus-which release a colored ink upon approach or attack. Previous work showed that ink can protect molluscs through a combination of chemical, visual, and other effects. In this study, we examined the effects of ink from longfin inshore squid, Doryteuthis pealeii, on the behavior of two species of predatory fishes, summer flounder, Paralichthys dentatus, and sea catfish, Ariopsis felis. Using a cloud assay, we found that ink from longfin inshore squid affected the approach phase of predation by summer flounder, primarily through its visual effects. Using a food assay, we found that the ink affected the consummatory and ingestive phase of predation of both sea catfish and summer flounder, through the ink's chemical properties. Fractionation of ink showed that most of its deterrent chemical activity is associated with melanin granules, suggesting that either compounds adhering to these granules or melanin itself are the most biologically active. This work provides the basis for a comparative approach to identify deterrent molecules from inking cephalopods and to examine neural mechanisms whereby these chemicals affect behavior of fish, using the sea catfish as a chemosensory model.

Cephalopod Ink: Production, Chemistry, Functions and Applications

“…For example, Staudinger et al [103] show in laboratory experiments that inking by Doryteuthis pealeii is correlated with changes in the attack behavior of predatory fishes, such as increases in startle behavior, abandonment of attacks by bluefish and misdirected attacks by flounder. Experimental studies are rarer and limited to laboratory simulations of predator-prey interactions, but they support a defensive role of ink by showing that a cloud of ink released between a piece of food and an approaching fish will slow the fish’s attack [55,104]. …”

“…Ink from two species of squid, the Caribbean reef squid, Sepioteuthis sepioidea , and the longfin inshore squid, Doryteuthis pealeii , is unpalatable to predatory fish and, as such, might provide a defense during attacks [55,104]. The molecular identities of these deterrents are unknown.…”

“…Tests of cephalopod ink as a phagomimetic defense have yielded mixed results. Ink from two species of squid was not found to be phagostimulants for predatory fish [55,104]. However, ink from octopus ink was found to be attractive to moray eels, evoking searching and attack behaviors, much as did food-related chemicals [117].…”

An elaborate behavioural sequence reinforces the decoy effect of ink during predatory attacks on squid

“…Since the pioneering study conducted by Hall (1956) that proposed that squid ink has a decoy effect on predators, few studies have considered this subject area. However, a recent experimental study by Wood et al (2010) showed that the ink pseudomorph produced by the Caribbean reef squid (Sepioteuthis sepioidea) significantly delays food capture by the predatory fish Haemulon flavolineatum by preventing it from receiving visual and chemical cues; Derby et al (2013) observed a similar effect in the longfin inshore squid (Doryteuthis pealeii). However, both these studies were conducted under experimental conditions and did not use live squid; thus, it is still unclear whether these effects can also occur in field conditions.…”

“…Inking has been proposed to have both chemical and visual effects on predators (Derby 2007), with the ink cloud acting as a decoy for squid and a smokescreen for cuttlefishes and octopuses (Hall 1956;Staudinger et al 2013;Hanlon and Messenger 2018). The use of ink as a defence mechanism has been proposed based on field observations (Moynihan and Rodaniche 1982;Hanlon and Messenger 1988;Caldwell 2005); however, only few studies have experimentally investigated how ink can confuse the predator and whether it acts as a pseudomorph (decoy) or a smokescreen (Wood et al 2010;Derby et al 2013).…”