Farming Tautog as a High Value Fish while Reducing Invasive Crab Populations

Part 1: Determining the impact of a natural diet on the growth and survival of Tautog (Tautoga onitis) in Recirculating Aquaculture Systems

During the month of April 2019, minnow traps baited with green crab were deployed in Megansett Harbor, MA (Figure 1, Location A). Traps were checked and rebaited every other day. However, the use of minnow traps proved highly inefficient with minimal to no weekly captures of tautog. Beach seining proved much more successful. During the months of May and June 2019 a series of beach seines were conducted at Megansett beach in North Falmouth, MA (Figure 1, Location A) and Monk’s Cove in Bourne, MA (Figure 1, Location B). Year 1 tautog ranging from 5.3 cm to 10.2 cm were kept from the beach seines and placed immediately in coolers upon capture. All bycatch was released back to the water at the respective sampling locations (Figure 1). Tautog within desired size rang (5 to 10 cm) were then transferred to lantern nets in Fiddlers Cove Marina in North Falmouth, MA, which in the same proximity as the Megansett Harbor sampling location (Figure 1, Location A).

All captured tautog were kept in lantern nets for at least 24 hours prior to transportation to UMASS Dartmouth wet lab location in New Bedford, MA. Until the required number of tautog were acquired (450 individuals) via beach seining, they were held in a flow through system at the wet lab facilities in New Bedford, MA. Once over 450 tautog had been transferred to the wet lab facilities, the tautog were divided into three separate treatment diets: 1) Natural: green crabs only; 2) Zeigler: commercially available marine finfish diet; 3) Natural + Zeigler: green crabs supplemented with commercial feed. At the initiation of the experiment, the 450 tautog used had a mean length of 7.9 cm (SE±0.1) ranging from 5.3 to 10.2 cm/individual and a mean weight of 7.3 grams (SE±0.2) ranging from 2 to 19 grams/individual. Each treatment was composed of three replicate 75L flow through tanks housing 50 tautog each. The replicate tanks had controlled temperature (~25^oC), salinity (30-32 psu), lighting (12L:12D) and aeration. Every 30 days, all tautog from each replicate were sampled for total length (cm) and weight (g). Additionally, while the tautog were being measured from each replicate, the tanks housing the replicates being measured were scrubbed of algae and then drained to promote aquaria cleanliness. Once tanks had fully drained and had fresh saltwater flow, the sampled tautog were returned to the respective tanks.

Feeding amounts were determined based on satiation and administered at each feeding interval. Increases in feeding were decided based on percent growth and satiation. Satiation was determined by whether there was any left-over food left in the tanks after feeding. Table 1 shows the 3 different commercial pellet feeds that have been used up to this point in the study. From July to October, we used the ‘starter with Vpak’, and we fed 10 grams per feeding, twice a day. For the first two weeks in October, we used a half and half blend of the starter feed with the fingerling starter feed to ensure that the fish of different sizes were receiving food. From October 17, 2019 to January 4, 2020 the diet used was the ‘fingerling starter with Vpak’. The fish received 20 grams of this food, per feeding. Starting on January 5, 2020, we began to use the ‘Hi-Performance’ marine finfish food from Zeigler. The amount was 30 grams of food, twice a day. The amount of food was determined by 2% of the total body weight and observational record of uneaten food in the tanks.

Table 1: Zeigler commercial feed composition and size used in this study

The amount of crab was determined by a total of 40% of the total weight of the fish, while also keeping track of whether or not all the food was being eaten in the tanks. Feeding to satiation while avoiding excess food in the tanks was important to ensure high water quality and growth. The amount of crab administered at each feeding, per month, is shown below in Table 2.

Table 2: amount of crab administered each month, per feeding

Statistical analyses were conducted in RStudio. Data of the mean daily growth rates, both in weight and length, of tautog from all three treatment groups for each sampling month were first tested for normal data distribution using a Shipiro-Wilks normality test. If data was normally distributed, an ANOVA was first conducted, and if a significant difference was present in the treatment groups, a Tukey post-hoc test was conducted. If the data was not normally distributed, then a Kruskal-Wallis test was conducted followed by Pair-Wise Wilcoxon post-hoc test.

Part 2: The Effects of Feed Attractants on the Growth of Tautog (Tautoga onitis) in Recirculating Aquaculture Systems

Worldwide, aquaculture growth and development are greater than any other food production sector, while the FAO monitoring of marine fishery resources has shown that landings are continuing to decline (FAO 2018). With declining fishery resources, the world must face the challenge of feeding its growing population. The growing industry of aquaculture has a wide range of impacts, and contributes to food security, employment, enhanced resource management, and sustainable farm practices (Halwart et al., 2003) Sustainable farm practices are a key initiative for stakeholders, managers, and farmers moving forward. Limitations in production, high prices of fish meal and fish oil, and increasing concern for environmental impact have prompted a desire to seek alternatives to fuel the aquaculture industry (Nagel et al., 2017;Tantikitti 2014;). Feed alone contributes to more than 50% of the cost production in intensive aquaculture systems, and is often the single greatest expense in aquaculture systems (Pavadi et al., 2012; Fast et al., 1997) Aquaculture expansion is reliant on systems that favor readily available species that are preferred for local consumption (Halwart et al., 2003). In the United States, this is a challenge worth addressing in terms of ecological impacts and sustainability of the growing aquaculture initiative.

Tautog (Tautoga onitis) is a marine wrasse native to western Atlantic communities, and extends from Nova Scotia to South Carolina, with the highest abundances noted from south of Cape Cod to the Delaware Capes (Bigelow and Schroeder 1953). Tautog exhibit strong site fidelity, low daily movement rates, and seasonal migration (Olla et al., 1974). These life history characteristics make this species vulnerable to fishing activity. From the most recent stock assessment produced by the Atlantic States Marine Fisheries Commission, (ASMFC) tautog have been identified as a species that is recreationally and commercially overfished, and overfishing is occurring (ASMFC 2017). Regional markets have supported recreational and commercial fishing of tautog for over a century. Records have shown that tautog appeared in fish markets in Boston as early as 1814, and in Wellfleet, hook and line fisheries have existed at least since 1839 (Bigelow and Schroeder 1953).

Due to its life history characteristics, fish market potential, and fishing pressures, tautog have been identified as an ideal candidate for marine aquaculture (Perry et al., 1998). Laboratory studies of tautog have shown that adults can be conditioned to induce natural spawning, and success has been noted in multiple locations in Rhode Island and Connecticut (Perry et al., 1998). A year-round supply of high-quality, market preferred fish would boost regional economies, and could relieve fishing pressures. Growth rates in laboratory studies have been shown to be significantly lower than in the wild, and authors have acknowledged a potential missing component in the commercial feed (Perry et al., 2001). A nutritional component may be contributing to low growth rates in juvenile tautog, however, other components of food and feeding behavior may also be a factor.

Poor attract -ability and palatability may be responsible for poor ingestion rates in some fish species (Ajiboye et al., 2012). In order to enhance these aspects of the finfish diet at a commercial scale, feed additives may provide a solution. Micro-bound particles allow for nutrients to bind and create a stable feed, examples of these include alginate, agar, carrageenan, starch, zein, and gelatin. This approach offers the advantages of economic viability and the not using toxic ingredients in order to make the food (Langdon 2003). Feed attractants have the potential to reduce feed waste, promote growth, and subsequently enhance the economic success of finfish aquaculture (Pavadi et al., 2012).

Various studies have documented the trials of feed attractants on various species that have also been noted to have regional economic importance and market potential. In particular, hydrolysis has been employed as a promising way for the conversion of fish-by-products into new and suitable forms (Khosravi et al., 2015) Low molecular weight and well balanced amino acid profiles have made hydrolysates a viable chemo-attractant and fish meal replacement in aquafeeds(Aksenes et al., 2006a; Kolkovski et al., 2000). Gelatin bound squid hydrolysates have been used in the aquaculture of cod and octopus with success (Kvåle et al., 2006; Quintana et al., 2008). Hydrolysis breaks down large protein chains into peptides and free amino acids.  Feeding behavior is stimulated by low molecular weight substances with higher solubility(Løkkeborg et al., 2014) Inclusion of hydrolysates as protein replacement may have a two-fold effect; one being that ingestion rates become higher and two being that there is higher assimilation due to the free amino acid and short peptides ( Kolkovski et al., 2000).

Olfactory and gustatory systems are the main centers for chemoreception in fish, odors may trigger food search, gustatory system may reject the object after tasting it (Løkkeborg et al., 2014).  Feed attractants are chemicals that orient an animal towards the source of the chemicals (Pavadi et al., 2012). Feed palatability in carnivorous aquaculture species shares a strong relationship with attractants that are associated with the prey components under wild conditions (Tantikitti 2014). When considering potential hydrolysates for tautog aquaculture, green crab may provide a solution, due to natural feeding habits. Dietary extracts from the tissues of prey species have been shown to stimulate feeding behavior (Løkkeborg et al., 2014). Further supporting this are studies documenting the success of crustacean meals in several aquaculture species, exhibiting positive results on palatability and growth performance (Toppe et al., 2006; Tibbets & Lall, 2013). In addition, attractants may provide a useful use of an otherwise underutilized marine resource.

Research Objective

The goals of the project were to determine the role of feed attractants in the growth of tautog in recirculating aquaculture systems. In order to achieve this research goal, the project identified alternative sources of protein to inform the aquaculture community of potential replacements for fish meal and fish oil as a primary protein source. This portion of the project has also being used for the MSc thesis for graduate student Michael Coute to be completed at the University of Massachusetts Dartmouth School for Marine Science & Technology.

Methods

 In June 2020, 450 year-1 (5-15 g) tautog were collected locally from Buzzards Bay, which hosts a relatively large population of fish which can be obtained by beach seine. The fish were brought to UMASS Saltwater Facility (New Bedford, MA) and introduced to a tank with flow-through seawater to acclimate. After 14 days, the fish were introduced to a heated saltwater recirculating system of 300-gallon aquaria with controlled temperature (20° C), lighting (12L:12D), constant salinity (30-32 psu) and aeration. The fish were separated into one of the three treatments (135 fish per treatment), each tank with 45 fish maintained in triplicate. The tautog were fed to satiation twice daily (08:00, and 16:00), with one of the three diets. Once all the fish were placed into tanks randomly, they were assigned one of three possible feeding treatments: crab hydrolysate, squid hydrolysate, or commercial feed. This resulted in triplicates of each diet. Feed was created on site through the process of hydrolysis. All feed treatments consisted of a 1.5mm standard commercial pellet purchased from Ziegler fish foods (Table 1). The pellets were coated in a non-flavored gelatin to ensure that the test variable is the hydrolysate. The designed feeding trials took place over 12 weeks, with growth measurements for total length and weight taken biweekly to assess growth over time.

Part 3: Determining the performance of Tautog (Tautoga onitis) fed a shrimp-meal based diet.

The first component of this project documented improved growth and survival of tautog when fed a diet of green crab.  However, the combination of cost, handling and the negative impacts on water quality made this diet commercially infeasible and non-scalable.  This component of the project attempted to address these issues by evaluating an alternative crustacean-based diet.  An experimental diet was created using dried shrimp meal.  Shrimp meal is a fisheries byproduct in which the carapace of commercial shrimp are dried and ground.  Shrimp meal is relatively cheap, accessible, and shelf-stable making it a potential candidate for fish meal replacement.  The goal of this experiment was to compare the growth and survival of juvenile tautog fed a shrimp meal-based diet compared to the commercial finfish diet.

Methods

Diet formulation

Dried shrimp meal was procured from Blum and Bergeron, Inc. (Houma, LA).  The shrimp meal was produced as a byproduct of the commercial “Gulf shrimp” fishery which may consist of pink shrimp (Penaeus duorarum), brown shrimp (Penaeus aztecus) or white shrimp (Penaeus setiferus).  The shrimp meal was formed into shrimp cakes to provide a desired texture and consistency for the fish.  Fish cakes were produced by combining 20 grams of dried shrimp meal with 80 grams of water and gelatin.  The water and gelatin were used at a ratio of 1 g dried powdered gelatin (Knox Unflavored Gelatin) to 17 g of water.  The mixture was placed into silicon molds and was allowed to set in a refrigerator overnight before use.  A commercial fish pellet (Zeigler Finfish Starter 3 mm pellet) was used as a control diet.  A sample of each diet was submitted to a laboratory (Eurofins Microbiology Laboratories, North Kingstown, RI) for proximate analysis.  The nutritional information for each diet can be found in Table 3. 

Table 3: Nutritional composition of each diet obtained by proximate analysis. NFE stands for “Nitrogen-Free Extract” which represents soluble carbohydrates.

Experimental Design

One hundred and twenty juvenile tautog were selected for use from the previous experiment.  The population was restricted to provide a relatively uniform distribution of length and weight.  From this population, tautog were randomly placed into one of six tanks (389 liters).  Each tank housed 20 tautog and was randomly assigned one of the two feeding treatments (shrimp meal or control).  All tanks were on a recirculating seawater system providing consistent and uniform water conditions with respect to temperature (20⁰C) and salinity (35 psu).  Dissolved oxygen was monitored daily.  Several sections of PVC pipe (4” diameter x 12” length) were placed in the tanks to provide structure which tautog prefer to reside in.

Tautog were fed to satiation twice daily (0900 and 1600).  Satiation was determined by observing excess food remaining in the tank during subsequent feedings.  Feeding rates were adjusted after each sampling period.  Initial feeding rates were based on the consumption observed in previous trials.  All excess feed was siphoned out of the tank every morning.  

Data Collection and Analysis

To evaluate the growth performance, the length and weight of all fish were measured biweekly with the feeding trials lasting six weeks.  A one-way ANOVA was used to evaluate the effects of the treatment on starting weight and length, finishing weight and length, and growth.